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Article

Microwave-Assisted Catalytic Transfer Hydrogenation of Chalcones: A Green, Fast, and Efficient One-Step Reduction Using Ammonium Formate and Pd/C

by
Wender Alves Silva
1,*,
Sayuri Cristina Santos Takada
2,
Felipe Marques Nogueira
1 and
Luiz Arthur Ramos Almeida
1
1
Laboratory for Bioactive Compound Synthesis, University of Brasilia (IQ-UnB), Campus Universitario Darcy Ribeiro, Brasilia 70904-970, Brazil
2
Embrapa Genetic Resources and Biotechnology, Empresa Brasileira de Pesquisa Agropecuaria, Brasilia 70770-917, Brazil
*
Author to whom correspondence should be addressed.
Organics 2025, 6(3), 40; https://doi.org/10.3390/org6030040
Submission received: 29 June 2025 / Revised: 21 August 2025 / Accepted: 22 August 2025 / Published: 3 September 2025
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Abstract

Catalytic transfer hydrogenation (CTH) and microwave-assisted organic synthesis (MAOS) have each advanced the sustainability of reduction chemistry; however, their combined application to conjugated enones remains largely unexplored. To the best of our knowledge, no unified protocol has been reported for the rapid, one-pot conversion of chalcones into saturated alcohols under microwave irradiation. Herein, we report a concise and green method that integrates MAOS with Pd/C-catalyzed CTH, employing inexpensive ammonium formate in ethanol. In contrast to state-of-the-art hydrogenations that require pressurized H2 or costly metal complexes, our strategy (i) achieves complete conversion within 20 min at 60 °C, (ii) tolerates both electron-rich and electron-poor substrates, (iii) reduces nitro-substituted chalcones in a single step, and (iv) consumes < 0.005 kWh per reaction—an approximately 250-fold energy saving relative to conventional procedures. These results position microwave-driven CTH as a scalable alternative for synthesizing pharmacologically relevant saturated alcohol scaffolds from readily available chalcones.

Graphical Abstract

1. Introduction

In both academic research and the pharmaceutical industry, the synthesis of drug candidates typically involves functional group transformations, many of which require reductive or oxidative steps throughout the development process. Reduction reactions constitute a fundamental class of transformations in organic chemistry, playing a pivotal role in the synthesis of structurally diverse natural products, pharmacologically active compounds, agrochemicals, and functionalized materials [1,2,3,4]. Within this context, the reduction of carbonyl compounds to their corresponding saturated alcohols is particularly significant due to its strategic value in preparing pharmaceutical intermediates and industrially relevant molecules; see Figure 1 [5,6,7,8,9,10,11].
Over the past few decades, considerable effort has been devoted to developing catalytic methodologies capable of effecting the complete reduction in α,β-unsaturated substrates (Scheme 1). Most protocols employ transition-metal catalysts—particularly rhodium, ruthenium, platinum, iridium, and related complexes—to chemoselectively hydrogenate the carbon–carbon double bond, thereby furnishing product A [12,13,14,15]. This selectivity often depends on careful control of the amount of hydrogen introduced, as well as on the nature of the metal, which is generally perceived as a key factor influencing the outcome.
These catalytic systems are typically used with a wide range of hydrogen donors, including molecular hydrogen, alcohols, formic acid, ammonium formate, DMSO, borohydrides, and (para)formaldehyde [16,17,18]. While generally effective, these approaches are often associated with significant drawbacks, including the high cost of catalysts, extended reaction times, the formation of toxic byproducts, and difficulties in product purification [19,20,21,22]. Such limitations may hinder broader application in industrial and pharmaceutical settings. In this context, catalytic transfer hydrogenation (CTH) has emerged as a valuable alternative to conventional hydrogenation methods, offering safer and faster reactions with high yields under both homogeneous and heterogeneous conditions (Scheme 2) [23,24,25,26,27,28,29,30,31,32]. Nevertheless, the development of robust and efficient CTH protocols employing stable and more environmentally friendly hydrogen donors—as substitutes for gaseous hydrogen, expensive catalysts, or highly toxic reagents—remains a major challenge and an important goal in the field.
Chalcones, also known as chalconoids, constitute a prominent class of biologically active molecules with considerable medicinal relevance. Structurally, they are α,β-unsaturated carbonyl compounds featuring a three-carbon core, commonly described as 1,3-diphenylprop-2-en-1-one. Their broad pharmacological potential continues to attract substantial interest in pharmaceutical and biomedical research, driving extensive investigations into their vast possibilities for structural modifications and derivative synthesis (Figure 2) [33,34,35,36,37,38]. Naturally occurring as a diverse group of secondary metabolites in numerous plant species, chalcones have long been associated with traditional medicinal and dietary applications [39,40]. They can be synthesized through several approaches, although the Claisen–Schmidt condensation [41] remains the most widely adopted, owing to its methodological simplicity and consistently high yields. Notably, reduced chalcone derivatives obtained via catalytic transformations serve not only as versatile intermediates—valuable building blocks—for the synthesis of bioactive compounds, but also exhibit excellent reproducibility and convergence, affording high yields and purity with minimal purification requirements. These attributes further enhance their utility in synthetic and medicinal chemistry.
Microwave-assisted organic synthesis (MAOS) has emerged as a transformative platform in modern synthetic chemistry, offering decisive advantages over conventional thermal methods in terms of efficiency, selectivity, and sustainability [42,43]. Unlike traditional conductive heating, microwave irradiation enables direct volumetric energy transfer, resulting in rapid, homogeneous heating, minimized thermal gradients, and significantly shortened reaction times. These features improve yields and purity, suppress undesired side reactions, and significantly reduce energy consumption. Notably, microwave reactors allow for safe operation under elevated pressures and temperatures in sealed vessels, enabling transformations that are often inaccessible using standard thermal conditions. From a green chemistry perspective, MAOS aligns closely with core sustainability principles—enhanced energy efficiency, reduced waste generation, and inherently safer reaction conditions—reinforcing its value as a powerful and environmentally benign synthetic methodology [44,45].
Despite these well-established advantages, the integration of MAOS with catalytic transfer hydrogenation (CTH) has been surprisingly limited. Previous applications have focused predominantly on simple substrates such as isolated ketones and nitroarenes, leaving conjugated enones—particularly chalcones—largely unexplored. This gap is particularly noteworthy considering the synthetic significance and medicinal relevance of chalcone derivatives. In this context, we aimed to bridge this methodological divide by combining MAOS with a low-loading Pd/C–ammonium formate system. To address this gap in the literature, we conducted a systematic investigation of the scarcely explored integration of microwave-assisted heating with catalytic transfer hydrogenation (CTH), a promising combination for the development of new synthetic methodologies. Specifically, this study (i) benchmark this integrated strategy against conventional thermal CTH and high-pressure hydrogenation protocols; (ii) demonstrate its operational simplicity, enhanced efficiency, and broad substrate scope; and (iii) deliver a genuinely green and scalable approach that employs biomass-derived ethanol as solvent and ammonium formate as a safe, non-toxic, and cost-effective hydrogen donor—culminating in significantly reduced energy consumption and environmental impact.

2. Materials and Methods

The chalcones had been previously synthesized by our research group. All reagents and solvents were purchased from Sigma-Aldrich-Merck (St. Louis, MO, USA). The microwave reactions were performed on a Biotage Initiator+ (Uppsala, Sweden), microwave reactor using sealed vessels, a dynamic program, temperature detection by internal fiber optic probe, simultaneous cooling, and media stirring. The NMR spectra were recorded at 25 °C on a Bruker Avance 600 spectrometer (Billerica, MA, USA, 600 MHz for 1H and 151 MHz for 13C) and Varian Mercury Plus spectrometer (Palo Alto, CA, USA, 300 MHz for 1H and 75 MHz for 13C) with TMS as an internal standard for deuterated chloroform (CDCl3) as solvent. The reactions were monitored by thin-layer chromatography (TLC) on precoated 0.25 mm thick plates of Kieselgel 60 F254 (Burlington, MA, USA), visualization was accomplished by UV light (254 nm) or by spraying a solution of 10% solution of phosphomolybdic acid in ethanol, followed by heating at 200 °C for a sufficient duration until blue spots become visible. HRESI-MS (ESI-QTOF) experiments were performed on a Triple Tof 5600 Sciex (Framingham, MA, USA), by flow injection analysis using an Eksigent UltraLC 100 Sciex chromatograph (Framingham, MA, USA), set to a flow rate of 0.3 mL/min.

General Microwave-Assisted Synthesis of Alcohol

A sealed 10 mL glass tube containing a mixture of chalcone (0.1 mmol), ammonium formate (0.8 mmol), and 5% Pd/C (0.005 mmol) in ethanol (5.0 mL) was placed in a microwave reactor (Biotage Initiator+, Uppsala, Sweden) and heated at 60 °C for 20 min under magnetic stirring. The progress of the reaction was monitored by thin-layer chromatography (TLC). After cooling to room temperature, the reaction mixture was filtered through a Celite pad to remove insoluble residues, and the filtrate was concentrated under reduced pressure. When necessary, the crude product was purified by column chromatography on silica gel using a 90:10 hexane/ethyl acetate mixture as the eluent.
A1. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.01–2.24 (2H, m), 2.73–2.84 (2H, m) 4.71–4.73 (1H, dd, J = 7.9 Hz, 5.3 Hz), 7.22–7.31 (3H, m), 7.32–7.38 (4H, m), 7.42–7.45 (3H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 32.1, 40.5, 73.9, 125.9, 127.7, 128.3, 128.4, 128.5, 141.8, 144.6. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C15H17O+: 213.1201 [M + H]+, found [M + H]+ 213.1200.
A2. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.02–2.20 (2H, m), 2.65–2.78 (2H, m), 3.84 (3H, s), 4.66–4.68 (1H, dd, J = 7.5 Hz, 5.8 Hz), 6.91–6.93 (2H, m), 7.21–7.32 (7H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 32.1, 40.4, 55.3, 73.5, 114.0, 125.9, 127.3, 128.4, 128.8, 140.6, 140.8, 141.8, 143.6. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C16H19O2+: 243.1307 [M + H]+, found [M + H]+ 243.1306.
A3. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.11–2.22 (2H, m), 2.74–2.82 (2H, m), 4.76–4.79 (1H, dd, J = 7.9 Hz, 5.3 Hz), 7.22–7.24 (3H, m), 7.25–7.29 (2H, m), 7.31–7.33 (1H, m), 7.36–7.48 (4H, m), 7.61–7.63 (4H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 32.1, 40.5, 73.7, 125.9, 126.4, 127.1, 127.3, 128.4, 128.8, 140.6, 140.8, 141.8, 143.6. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C21H21O+: 289.1514 [M + H]+, found [M + H]+ 289.1515.
A4. 1H NMR (600 MHz, CDCl3) δ (ppm): 1.94–2.09 (2H, m), 2.54–2.63 (2H, m), 3.05 (1H, bs), 4.64–4.68 (1H, dd, J = 7.8 Hz, 5.4 Hz); 13C NMR (151 MHz, CDCl3) δ (ppm): 31.1, 40.7, 73.7, 100.7, 108.1, 108.9, 121.1, 125.9, 127.6, 128.5, 135.6, 144.5, 145.6, 147.6. Yield 80%. HRESI-MS (ESI-QTOF): calculated for C15H18NO+: 228.1310 [M + H]+, found [M + H]+ 228.1312.
A5. 1H NMR (600 MHz, CDCl3) δ (ppm): 1.99–2.14 (2H, m), 2.22 (1H, bs), 2.60–2.72 (2H, m), 4.69–4.71 (1H, dd, J = 7.9 Hz, 5.3 Hz), 5.94 (2H, S), 6.66–6.76 (3H, m), 7.30–7.38 (5H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 31.8, 40.7, 73.7, 100.7, 108.1, 108.9, 121.1, 125.9, 127.6, 128.5, 135.6, 144.5, 145.6, 147.6. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C16H17O3+: 257.1099 [M + H]+, found [M + H]+ 257.1097.
A6. 1H NMR (600 MHz, CDCl3) δ (ppm): 1.22–1.27 (3H, t, 7.2Hz), 1.96–2.08 (2H, m), 2.57–2.68 (2H, m), 3.69–3.76 (2H, q, J = 14.3Hz, 7.0Hz), 4.64–4.65 (1H, dd, 7.8 Hz, 5.6 Hz), 5.95 (2H, s), 6.65–6.77 (4H, m), 6.90–6.92 (2H, m), 7.28–7.30 (2H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 14.3, 31.9, 40.6, 61.6, 65.3, 73.3, 100.8, 108.1, 108.9, 113.8, 121.2, 127.2, 130.4, 135.7, 136.7, 145.6, 147.6, 159.1. Yield 95%. HRESI-MS (ESI-QTOF): calculated for C20H23O6+: 359.1416 [M + H]+, found [M + H]+ 359.1416.
A7. 1H NMR (600 MHz, CDCl3) δ (ppm): 1.94–2.14 (2H, m), 2.57–2.68 (2H, m), 3.83 (3H, s), 4.63–4.65 (1H, dd, J = 7.8 Hz, 5.6 Hz), 5.95 (2H, s), 6.65–6.77 (3H, m), 6.90–6.92 (2H, m), 7.28–7.30 (2H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 31.9 40.6, 55.3, 73.6, 100.8, 108.2, 108.9, 113.9, 121.2, 127.2, 130.4, 135.7, 136.7, 145.6, 147.6, 159.1. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C17H19O4+: 287.1205 [M + H]+, found [M + H]+ 287.1203.
A8. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.07–2.27 (2H, m), 2.64–2.76 (2H, m), 4.85–4.87 (1H, dd, J = 8.4Hz, 5.3 Hz), 5.95 (2H, s), 6.67–6.69 (3H, m), 6.72–6.96 (3H, m), 7.19–7.21 (1H, m), 12.31 (1H, s); 13C NMR (151 MHz, CDCl3) δ (ppm): 31.7, 38.6, 75.3, 100.8, 108.9, 117.3, 119.8, 121.2, 127.1, 129.1, 135.0, 145.8, 147.7, 155.6. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C16H17O4+: 273.1049 [M + H]+, found [M + H]+ 273.1046.
A9. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.01–2.16 (2H, m), 2.62–2.69 (2H, m), 2.94 (6H, s), 4.70–4.73 (1H, dd, J = 7.9 Hz, 5.3 Hz), 6.73–6.76 (2H, m), 7.10–7.12 (2H, m), 7.29–7.38 (5H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 31.0, 40.7, 41.0, 74.0, 113.3, 126.0, 127.6, 128.5, 129.1, 130.1, 144.7, 149.0. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C17H22NO+: 256.1623 [M + H]+, found [M + H]+ 256.1620.
A10. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.13–2.17 (2H, m), 2.25 (1H, s), 2.60–2.71 (2H, m), 2.95 (6H, s), 4.70–4.73 (1H, dd, J = 7.9 Hz, 5.3 Hz), 6.74–6.75 (2H, m), 7.31–7.39 (5H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 31.0, 40.8, 10.9, 73.9, 113.2, 126.0, 127.5, 128.5, 129.0, 130.0, 144.8, 149.1. Yield 97%. HRESI-MS (ESI-QTOF): calculated for C17H21ClNO+: 290.1233 [M + H]+, found [M + H]+ 290.1231.
A11. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.01–2.20 (2H, m), 2.65–2.76 (2H, m), 2.94 (6H, s), 3.84 (3H, s), 4.66–4.68 (1H, dd, J = 7.8 Hz, 5.6 Hz), 6.91–6.92 (2H, m), 7.21–7.22 (2H, m), 7.29–7.32 (4H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 31.1, 40.3, 41.0, 55.3, 73.5, 113.7, 125.8, 127.2, 128.4, 136.7, 141.8, 159.1. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C18H24NO2+: 286.1729 [M + H]+, found [M + H]+ 286.1727.
A12. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.01–2.19 (2H, m), 2.65–2.77 (2H, M), 3.83 (3H, s), 4.66–4.68 (1H, dd, J = 7.7 Hz, 5.6 Hz), 6.91–6.92 (2H, m), 7.21–7.29 (2H, m), 7.30–7.35 (4H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 32.1, 40.3, 55.3, 73.5, 113.7, 113.9, 125.8, 127.2, 128.3, 136.7, 141.8, 159.1. Yield 98%. HRESI-MS (ESI-QTOF): calculated for C16H18ClO2+: 277.0917 [M + H]+, found [M + H]+ 277.0915.
C13. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.97–3.00 (2H, m); 3.17– 3.19 (2H, m), 5.94 (2H, s), 6.65–6.677 (3H, m), 7.15–7.17 (2H, m), 7.82–7.85 (2H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 30.3, 40.0, 100.8, 108.9, 113.8, 115.1, 121.1, 127.2, 130.8, 135.5, 145.8, 147.6, 151.0, 197.5. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C16H16NO3+: 270.1052 [M + H]+, found [M + H]+ 270.1050.
A14. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.00–2.20 (2H, m), 2.70–2.80 (2H, m), 4.71–4.73 (1H, dd, J = 7.6 Hz, 5.7 Hz), 7.31–7.41 (8H, m), 7.47–7.49 (1H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 32.1, 40.5, 73.9, 125.9, 127.6, 128.3, 128.4, 128.5, 130.4, 135.5, 144.6. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C15H16ClO+: 247.0811 [M + H]+, found [M + H]+ 247.0810.
A15. 1H NMR (600 MHz, CDCl3) δ (ppm): 1.99–2.22 (2H, m), 2.80–3.20 (2H, m), 3.21 (1H, bs), 4.68–4.72 (1H, dd, J = 7.7 Hz, 5.8 Hz), 6.89–7.11 (6H, m), 7.41–7.58 (2H, m), 7.62–7.77 (1H, m), 12.83 (1H, s); 13C NMR (151 MHz, CDCl3) δ (ppm): 29.6, 40.9, 73.9, 118.7, 124.2, 126.6, 128.9, 129.5, 136.2, 141.2, 144.8, 173.1. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C16H17O3+: 257.1099 [M + H]+, found [M + H]+ 257.1100.
A16. 1H NMR (600 MHz, CDCl3) δ (ppm): 1.61–1.88 (2H, m), 2.00 (1H, bs), 2.30–2.51 (2H, m), 4.66–4.68 (1H, dd, J = 7.8 Hz, 5.6 Hz), 6.50–6.53 (1H, m), 6.71–6.74 (1H, m), 7.28–7.71 (5H, m), 8.00–8.18 (1H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 32.7, 40.2, 73.9, 105.9, 112.31, 126.8, 128.4, 128.7, 141.5, 144.8, 155.6. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C16H20NO2+: 203.0994 [M + H]+, found [M + H]+ 203.0992.
C17. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.97–2.99 (2H, m), 3.00–3.19 (2H, m), 3.84 (3H, s), 6.43–6.46 (2H, m), 6.67–6.74 (3H, m), 7.15–7.17 (1H, m), 7.85–7.87 (2H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 26.5, 38.1, 55.7, 56.3, 101.0, 107.5, 114.8, 124.3, 126.7, 129.9, 152.6, 158.9, 199.6. Yield 95%. HRESI-MS (ESI-QTOF): calculated for C17H20NO3+: 286.1365 [M + H]+, found [M + H]+ 286.1362.
C18. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.93–2.96(6H, s), 2.94–2.96 (2H, m), 3.14–3.16 (2H, m), 6.63–6.71 (4H, m), 7.12–7.14 (2H, m), 7.81–7.82 (2H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 29.6, 40.3, 40.9, 113.1, 113.8, 127.7, 128.9,129.8, 130.5, 149.2, 150.9, 197.9. Yield 96%. HRESI-MS (ESI-QTOF): calculated for C17H21N2O+: 269.1576 [M + H]+, found [M + H]+ 269.1574.
A19. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.02–2.20 (2H, m), 2.65–2.78 (2H, m), 3.84 (3H, s), 4.66–4.68 (1H, dd, J = 7.7 Hz, 5.8 Hz), 6.60–6.63 (2H, m), 6.97–6.99 (2H, m), 7.28–7.35 (5H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 32.1, 40.3, 55.3, 73.5, 114.0, 125.8, 127.2, 128.4, 128.5, 132.6, 136.7, 145.9, 159.2. Yield 81%. HRESI-MS (ESI-QTOF): calculated for C16H20NO2+: 258.1416 [M + H]+, found [M + H]+ 258.1414.
A20. 1H NMR (600 MHz, CDCl3) δ (ppm): 1.94–2.09 (2H, m), 2.54–2.63 (2H, m), 3.05 (3H, bs), 4.64–4.68 (1H, dd, J = 7.8 Hz, 5.7 Hz), 6.43–6.46 (1H, m), 6.60–6.63 (1H, m), 6.96–6.99 (1H, m), 7.28 (1H, s), 7.29–7.35 (5H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 30.3, 40.1, 73.8, 108.3, 108.9, 115.1, 126.2, 127.4, 130.2, 135.8, 145.9, 147.8, 151.1. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C15H18NO+: 228.1310 [M + H]+, found [M + H]+ 228.1310.
A21. 1H NMR (600 MHz, CDCl3) δ (ppm): 1.92–2.21 (2H, m), 2.67–2.89 (2H, m), 4.62–4.66 (1H, dd, J = 7.5 Hz, 5.6 Hz), 6.56–6.59 (1H, m), 6.67–6.74 (1H, m), 6.86–6.92 (1H, m), 6.97–7.04 (1H, m), 7.18–7.35 (5H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 30.1, 40.4, 73.9, 123.1, 123.3, 127.7, 129.8, 130.9, 133.1, 134.5, 140.9, 143.1. Yield 100%. HRESI-MS (ESI-QTOF): calculated for C15H18NO+: 228.1310 [M + H]+, found [M + H]+ 228.1309.
C5. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.94–3.03 (2H, m), 3.23–3.26 (2H, m), 5.95 (2H, s), 6.65–6.74 (3H, m), 7.47–7.62 (3H, m), 7.93–7.99 (2H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 29.9, 40.7, 100.9, 108.3, 108.9, 121.2, 128.6, 128.1, 133.1, 135.1, 136.9, 145.9, 199.2. Yield 58%. HRESI-MS (ESI-QTOF): calculated for C16H15O3+: 255.0943 [M + H]+, found [M + H]+ 255.0942.
D5. 1H NMR (600 MHz, CDCl3) δ (ppm): 2.01–2.04 (2H, m), 2.61–2.63 (4H, m), 5.95 (2H, s), 6.74–6.75 (3H, m), 7.21–7.27 (5H, m); 13C NMR (151 MHz, CDCl3) δ (ppm): 31.7, 38.5, 38.7, 100.9, 108.3, 108.9, 117.4, 119.9, 121.2, 127.3, 129.1, 135.0, 145.9, 147.9, 155.7. Yield 80%. HRESI-MS (ESI-QTOF): calculated for C16H17O2+: 241.1150 [M + H]+, found [M + H]+ 241.1150.

3. Results and Discussion

The methodology presented herein features a palladium-catalyzed catalytic transfer hydrogenation (CTH) system of notable simplicity and efficiency, employing ammonium formate as the hydrogen donor and ethanol—a biomass-derived and environmentally benign solvent—as the reaction medium. This system enables the effective and high-yielding reduction in chalcones, a representative class of α,β-unsaturated ketones bearing various substituents on the aromatic rings.
Although sodium borohydride (NaBH4) remains a widely used reducing agent in organic synthesis due to its low cost, operational simplicity, and relatively benign environmental profile, its application to the reduction in α,β-unsaturated ketones such as chalcones often yields unsatisfactory results. A major drawback lies in its poor chemoselectivity, frequently resulting in incomplete reduction in the conjugated system and predominant formation of undesired allylic alcohols [46,47]. These shortcomings become particularly pronounced in substrates bearing electron-withdrawing groups or significant steric hindrance, conditions under which NaBH4 typically fails to deliver clean or complete conversions, often resulting in product mixtures and inconsistent yields [48]. Of particular concern, NaBH4-mediated reductions produce boron-containing waste, which complicates purification and raises concerns regarding environmentally sound disposal—factors that severely limit its utility in sustainable or large-scale applications.
In contrast, ammonium formate has proven to be a highly advantageous hydrogen donor in CTH reactions. It is non-toxic, inexpensive, easy to handle, and thermally decomposes under mild conditions to release hydrogen in situ, thereby eliminating the need for pressurized H2 gas or hazardous external reductants [49]. Compared to other hydrogen sources, ammonium formate offers excellent solubility in polar solvents, broad compatibility with diverse functional groups, and a low environmental footprint. Its solid, non-volatile nature ensures safe handling and convenient storage, making it well-suited for both academic research and industrial applications. Additionally, its decomposition byproducts—carbon dioxide and ammonia—are volatile and easily removed, simplifying post-reaction workup and enhancing the overall sustainability of the process. In the present study, ammonium formate was selected for these favorable characteristics, while ethanol was chosen as a green solvent in accordance with the principles of sustainable chemistry [50].
Other approaches reported in the literature, such as Zn/NH4Cl systems [51] and metal-free protocols employing water as the solvent in combination with a suitable hydrogen source, have also been explored [52], and suffer from major drawbacks, including narrow substrate scope, operational complexity, and the use of toxic or non-renewable reagents. In this context, our methodology stands out as a robust, scalable, and environmentally responsible alternative for the reduction in chalcones to saturated alcohols—offering a balance between synthetic efficiency and ecological sustainability.
Taken together, this comparative analysis highlights the practical and environmental limitations of traditional reducing agents such as NaBH4, while clearly emphasizing the unique advantages of our microwave-assisted Pd/C–ammonium formate protocol. The reactions proceed rapidly, affording quantitative yields of the desired saturated products within just 20 min, even at low catalyst loadings—matching or surpassing the results achieved with established procedures. Given the well-documented utility of microwave-assisted CTH in the reduction of carbonyl compounds and the notable lack of studies applying this approach to chalcone reduction, we sought to address this gap. Accordingly, we investigated a structurally diverse set of chalcones, previously synthesized in our laboratory, encompassing a broad range of electronic properties (Figure 3), using our optimized protocol under basic conditions [37]. This series allowed us to evaluate how substituent electronics influence reaction outcomes and to explore substrate reactivity profiles, with particular attention to the positional effects of substituents on the aromatic rings.
To date, no established CTH protocols have explored the reduction in chalcone substrates under microwave irradiation. To date, the only precedent is the study by Andrade et al. in 2006, which utilized a Pd/C–ammonium formate system in methanol, but required prolonged reaction times (2–6 h), elevated catalyst loadings, and substantial energy input [24]. Inspired by these findings, we conducted a systematic investigation to optimize the reaction conditions under microwave-assisted heating. The optimization results are summarized in Table 1.
For these experiments, chalcone 5 was selected as the model substrate. To reduce palladium usage, a catalyst loading of 5 mol% was employed, utilizing 5 wt% palladium on activated carbon. The initial experiments were carried out using 2 and 4 equivalents of ammonium formate under milder temperature conditions (entries 1 and 2). Under these conditions, the reaction required a relatively extended time to reach full conversion, yielding outcomes comparable to those previously reported by Andrade et al. [24]. The reaction mixture enabled the identification and separation of unreacted starting material, the corresponding saturated ketone, and the desired saturated alcohol, which was obtained as the major product. When the same reagent proportions were applied but with shorter reaction times (entries 3 and 4), the products consisted mainly of unreacted starting material and the saturated ketone, with no evidence of saturated alcohol formation as determined by TLC or 1H NMR analysis, as detailed in the Supporting Materials.
Upon increasing the temperature while maintaining the other conditions described in entry 4, a slight improvement was observed in the formation of the saturated alcohol, with the saturated ketone appearing only as a minor byproduct and no detectable starting material. Subsequent efforts focused on optimizing the amount of ammonium formate to achieve complete conversion under milder conditions, as evaluated in entries 6 and 7. Entry 7 provided the optimal conditions for the exclusive formation of the saturated alcohol, affording excellent yields (up to 99%). Based on this result, attention was then directed toward optimizing the reaction time. Entry 8 revealed the most efficient conditions for obtaining the desired product. In entries 9, 10, and 11, the reaction time was progressively shortened to assess whether high yields could still be achieved under shorter heating durations; however, this was not observed. Notably, under none of the conditions tested was any increase in pressure observed within the sealed reaction vessel during microwave irradiation.
To evaluate the limits of the reaction under the stoichiometric conditions described in entry 8, an important observation was made: extending the reaction time to 60 min led to the complete reduction in the α,β-unsaturated system, resulting in complete reduction to the corresponding alkane rather than the desired saturated alcohol (see Supporting Materials). This outcome is likely attributed to the use of excess ammonium formate in a sealed reaction vessel, which may facilitate further hydrogenation steps. Under these conditions, a pressure of 10 bar was recorded, indicating that the saturated alcohol intermediate remains susceptible to reduction, ultimately yielding the corresponding alkane (D5), as illustrated in Scheme 3. In light of this finding, additional studies will focus on the behavior of sensitive functional groups such as carboxylic acids, esters, and nitro groups, highlighting the promise of this methodology for reducing labile functionalities under milder and faster conditions than previously reported [53,54,55].
Having established the optimal reaction conditions, a comparative analysis was conducted to evaluate the effects of microwave irradiation versus conventional heating on yield and chemoselectivity. To this end, the substrate scope was expanded to include a structurally diverse series of chalcones bearing substituents at different positions on the aromatic rings—including functionally sensitive groups such as nitro moieties. The outcomes of this investigation are presented in Table 2.
The results presented in Table 2 offer unequivocal and compelling evidence of the efficiency, robustness, and broad applicability of the developed microwave-assisted catalytic transfer hydrogenation (CTH) methodology for the reduction in chalcones bearing a wide range of substituents. Under the optimized conditions, the protocol consistently furnished the corresponding saturated alcohols in excellent yields—ranging from 75% to quantitative—demonstrating high reactivity irrespective of the electronic nature of the substituents, whether electron-donating or electron-withdrawing. It is worth highlighting that a remarkable degree of chemoselectivity was observed throughout.
Chalcones containing exclusively electron-donating groups, such as N,N-dimethyl, hydroxy, methylenedioxy, and methoxy substituents (e.g., entries 2, 5, 7, 8, 9, and 11), consistently afforded very high to quantitative yields. These findings confirm that activating groups do not interfere with the hydrogenation process. It is also noteworthy that substrates bearing either sterically bulky or reduction-sensitive substituents—such as esters and carboxylic acids (e.g., entries 6 and 15)—underwent efficient conversion, indicating that neither steric hindrance nor electronic effects significantly limit the reduction under microwave-assisted conditions. Notably, compound A6 exhibited excellent chemoselectivity: the ester moiety remained unaltered, yielding exclusively the corresponding saturated alcohol. This outcome underscores one of the major advantages of microwave irradiation—enhanced mass transfer and homogeneous heating—which facilitates efficient transformations even in heterogeneous catalytic systems and mitigates steric constraints commonly encountered in conventional methodologies.
Similarly, halogenated chalcones (e.g., entries 10, 12, and 14) afforded near-quantitative yields, slightly lower than those of other substrates, possibly due to coordination effects with palladium or the electron-withdrawing nature of halogens. Importantly, no significant side reactions were detected, confirming the method’s selectivity.
A particularly noteworthy aspect of this methodology is its superior energy efficiency. The total energy consumption under microwave conditions was approximately 0.005 kWh—dramatically lower than the ~1.2 kWh typically required by conventional hydrogenation systems. Full details of these calculations are provided in the Supplementary Materials. This significant energy savings further underscores the method’s consistency with the fundamental principles of green chemistry [56].
Under conventional thermal heating conditions (Condition B: oil bath at 60 °C for 20 min), the catalytic transfer hydrogenation reactions exhibited markedly poor performance, with yields of the desired saturated alcohols consistently ranging between 3 and 7%. In nearly all cases, approximately 90% of the starting chalcone material was recovered, indicating minimal or negligible conversion. Notably, even substrates that responded efficiently under microwave irradiation failed to undergo effective transformation under conventional conditions. This discrepancy can be attributed to several factors: inefficient heat transfer in heterogeneous systems, insufficient thermal activation within the short reaction timeframe to promote effective decomposition of ammonium formate, and the inability to overcome kinetic barriers under isothermal conditions characterized by limited thermal gradients. In contrast, microwave irradiation promotes rapid, homogeneous volumetric heating, enhancing molecular collisions and solubility—key parameters in multiphasic systems such as Pd/C–formate–substrate mixtures. This effect is particularly evident in substrates bearing sensitive functionalities, such as esters (e.g., A6), which remained intact, reflecting a highly selective reactivity window favoring reduction in the α,β-unsaturated moiety over other functionalities. From a green chemistry perspective, the energy consumption under microwave conditions was estimated at ≤0.005 kWh per reaction—approximately 250 times lower than conventional methods. Importantly, the protocol obviates the use of pressurized hydrogen, employs biomass-derived ethanol as a green solvent, and relies on safe, low-cost reagents such as ammonium formate and Pd/C. Collectively, the data presented in Table 2 clearly demonstrate that microwave-assisted CTH significantly enhances both yield and chemoselectivity while offering major advantages in energy efficiency, safety, and sustainability. The stark contrast between Conditions A and B underscores that the success of the transformation hinges not merely on reagent composition, but critically on the mode of energy input. Thus, the developed protocol emerges as a practical, scalable, and environmentally responsible strategy for the synthesis of pharmacologically relevant saturated alcohols from readily accessible chalcones.
In contrast to the outcome observed for chalcone 4, chalcone 13—also bearing a strongly deactivating nitro group—exclusively yielded the saturated ketone bearing an amino group, indicating simultaneous reduction in both the olefinic bond and the nitro functionality. This result highlights the system’s ability to efficiently promote multi-site reductions in a single step, as illustrated in Scheme 4. To assess the generality of this behavior, two additional chalcones featuring the same substitution pattern—nitro group on the acetophenone-derived ring—were investigated. In both cases, the major product was the saturated ketone with an amino group, further confirming the observed trend.
Under the studied conditions, both chalcone 17 and chalcone 18 predominantly afforded the saturated ketone bearing an amino-substituted aromatic ring after 20 min of reaction. However, upon extending the reaction time, a nearly equimolar mixture of the corresponding saturated alcohol and the saturated ketone—both exhibiting the same amino substitution pattern on the aromatic ring—was observed. This trend suggests that prolonged reaction times promote further reduction in the carbonyl group, although with significantly lower overall yields.
The behavior of chalcones 19, 20, and 21 was very similar to that of chalcone 4, as both compounds share the same substitution pattern on the aromatic ring. In this case, complete reduction in the α,β-unsaturated system and the nitro group was achieved within 20 min, affording the saturated alcohol bearing an amino-substituted aromatic ring as the major product, in good yield. Extending the reaction time did not result in any significant change in yield. Taken together, these results suggest that electronic effects associated with the position of the nitro group—whether on the aldehyde- or ketone-derived aromatic ring—may play a significant role in modulating both the selectivity and efficiency of the reduction process, as detailed in Table 3.
This level of chemoselectivity is highly advantageous from a synthetic standpoint, as it eliminates the need for multi-step protocols typically required for nitro group reduction, thereby streamlining access to multifunctional intermediates. Notably, the reaction yields remained comparable regardless of the nitro group’s position on the aromatic ring (ortho, meta, or para), suggesting that positional effects exert minimal influence under the optimized conditions. These findings provide further support for the existence of alternative, competing reduction pathways involving both the α,β-unsaturated system and the nitro functionality. The formation of specific products—namely, a saturated ketone and an amine—indicates that the reducing system displays greater reactivity toward olefinic and nitro groups than toward the carbonyl moiety. This behavior is consistent with the well-established low oxophilicity of palladium, as previously demonstrated in the initial study (Table 2), where insufficient reaction times or substoichiometric amounts of ammonium formate resulted in the accumulation of the saturated ketone. Nevertheless, the newly obtained results fall within a synthetically useful and practically acceptable range of yields, further reinforcing the applicability of this method to preparative-scale transformations.

4. Conclusions

We have developed a microwave-assisted catalytic transfer hydrogenation (CTH) protocol employing Pd/C and ammonium formate that represents a significant advancement over conventional methods for the reduction in α,β-unsaturated ketones. Operating under mild conditions (60 °C, 20 min, 5 mol% Pd/C, ethanol), this method efficiently converts a structurally diverse array of chalcones into the corresponding saturated alcohols with outstanding yields and excellent chemoselectivity—even in the presence of sensitive functional groups such as nitro, ester, and halide substituents.
Compared to traditional thermal CTH, this microwave-based protocol offers multiple advantages: it reduces reaction times by up to two orders of magnitude, lowers catalyst loading, and minimizes energy consumption to less than 0.005 kWh per reaction—an approximately 250-fold decrease. These features align with the principles of green chemistry, particularly through the use of a biomass-derived solvent, the elimination of pressurized hydrogen gas, and the replacement of hazardous reducing agents with inexpensive, bench-stable ammonium formate.
The system enables site-selective and even concurrent reductions in C=C, C=O, and –NO2 moieties, providing rapid access to multifunctional scaffolds that would otherwise require stepwise synthesis. This reactivity—combined with operational simplicity, scalability, and environmental compatibility—highlights the synthetic utility and practical relevance of the method.
Ongoing efforts are focused on elucidating the mechanistic basis of this transformation and integrating the protocol with enantioselective strategies, such as enzymatic kinetic resolution, to access optically enriched products. Altogether, the findings presented here establish microwave-assisted CTH as a robust, sustainable, and versatile platform for the construction of saturated alcohol motifs with broad applicability in medicinal chemistry and related fields.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/org6030040/s1, detailed HRESI-MS (ESI-QTOF), 1H NMR, and 13C NMR spectral data for compounds Figures S1–S19, are reported in references [19,20,21,22,23,24,25,26,27,28,29,30,31,32]. The remaining figures are as follows: Figure S20. HRMS (ESI-QTOF) of compound A10 for [M + H]+; Figure S21. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of A11; Figure S22. HRMS (ESI-QTOF) of compound A11 for [M + H]+; Figure S23. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of A12; Figure S24. HRMS (ESI-QTOF) of compound A12 for [M + H]+; Figure S25. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of C13; Figure S26. HRMS (ESI-QTOF) of compound C13 for [M + H]+; Figure S27. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of A14; Figure S28. HRMS (ESI-QTOF) of compound A14 for [M + H]+; Figure S29. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of A15; Figure S30. HRMS (ESI-QTOF) of compound A15 for [M + H]+; Figure S31. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of A16; Figure S32. HRMS (ESI-QTOF) of compound A16 for [M + H]+; Figure S33. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of C17; Figure S34. HRMS (ESI-QTOF) of compound C17 for [M + H]+; Figure S35. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of C18; Figure S36. HRMS (ESI-QTOF) of compound C18 for [M + H]+; Figure S37. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of A19; Figure S38. HRMS (ESI-QTOF) of compound A19 for [M + H]+; Figure S39. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of A20; Figure S40. HRMS (ESI-QTOF) of compound A20 for [M + H]+; Figure S41. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of A21; Figure S42. HRMS (ESI-QTOF) of compound A21 for [M + H]+; Figure S43. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of C5; Figure S44. HRMS (ESI-QTOF) of compound C5 for [M + H]+; Figure S45. 1H NMR (600 MHz, CDCl3) and 13C NMR (151 MHz, CDCl3) of D5; Figure S46. HRMS (ESI-QTOF) of compound D5 for [M + H]+.

Author Contributions

Conceptualization, W.A.S. and S.C.S.T.; methodology, W.A.S., S.C.S.T., F.M.N., and L.A.R.A.; investigation, W.A.S., F.M.N., and L.A.R.A.; writing—review and editing, W.A.S., F.M.N., and S.C.S.T. All authors have read and agreed to the published version of the manuscript.

Funding

This work received financial support from the National Council of Technological and Scientific Development (CNPq), Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES) and University of Brasilia (UnB).

Data Availability Statement

Data are contained within the article and the Supplementary Materials.

Acknowledgments

The authors thank N.T.S., K.T.S., and IQ-UnB.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
1H NMRProton nuclear magnetic resonance
13C NMRCarbon-13 nuclear magnetic resonance
CTHCatalytic transfer hydrogenation
HRESI-MSHigh-resolution electrospray ionization mass spectrometry
MAOSMicrowave-assisted organic synthesis
TLCThin-layer chromatography

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Organics 06 00040 g001
Figure 1. Strategic value of reducing α,β-unsaturated carbonyls to saturated alcohols.
Figure 1. Strategic value of reducing α,β-unsaturated carbonyls to saturated alcohols.
Organics 06 00040 g001
Organics 06 00040 sch001
Scheme 1. Key reduction pathways of α,β-unsaturated carbonyl systems, A (ketones), B (allylic alcohols), and C (saturated alcohols).
Scheme 1. Key reduction pathways of α,β-unsaturated carbonyl systems, A (ketones), B (allylic alcohols), and C (saturated alcohols).
Organics 06 00040 sch001
Organics 06 00040 sch002
Scheme 2. Common hydrogen donors in CTH and their limitations.
Scheme 2. Common hydrogen donors in CTH and their limitations.
Organics 06 00040 sch002
Organics 06 00040 g002
Figure 2. Chalcones and derivatives: structural diversity and bioactivity.
Figure 2. Chalcones and derivatives: structural diversity and bioactivity.
Organics 06 00040 g002
Organics 06 00040 g003
Figure 3. Chalcone substrates evaluated under microwave-assisted CTH.
Figure 3. Chalcone substrates evaluated under microwave-assisted CTH.
Organics 06 00040 g003
Organics 06 00040 sch003
Scheme 3. Proposed route for full reduction under microwave conditions.
Scheme 3. Proposed route for full reduction under microwave conditions.
Organics 06 00040 sch003
Organics 06 00040 sch004
Scheme 4. One-step microwave reduction in nitro chalcones.
Scheme 4. One-step microwave reduction in nitro chalcones.
Organics 06 00040 sch004
Table 1. Optimization of CTH conditions for chalcone 5.
Table 1. Optimization of CTH conditions for chalcone 5.
Organics 06 00040 i001
EntryTemp. (°C)Time (min)NH4HCO2 (Equiv.)Major ProductYield (%)
140602C558
240604A562
340302C540
440304A553
560304A559
660306A580
760308A5100
860208A5100
96058C538
1060108A545
1160158A572
1260608D580
Table 2. Yields of saturated alcohols from substituted chalcones.
Table 2. Yields of saturated alcohols from substituted chalcones.
Organics 06 00040 i002
EntryConditions 1ProductYield (%)
1AOrganics 06 00040 i003100
B5 *
2AOrganics 06 00040 i004100
B3 *
3AOrganics 06 00040 i005100
B6 *
4AOrganics 06 00040 i00680 2
B3 *
5AOrganics 06 00040 i007100
B7 *
6AOrganics 06 00040 i00895
B5 *
7AOrganics 06 00040 i009100
B6 *
8AOrganics 06 00040 i010100
B4 *
9AOrganics 06 00040 i011100
B6 *
10AOrganics 06 00040 i01297
B3 *
11AOrganics 06 00040 i013100
B7 *
12AOrganics 06 00040 i01498
B3 *
13AOrganics 06 00040 i015100 3
B4 *
14AOrganics 06 00040 i016100
B5 *
15AOrganics 06 00040 i017100
B4 *
16AOrganics 06 00040 i018100
B5 *
1 Reaction conditions A: HCO2−NH4+, Pd/C 5%, microwave heating, 60 °C, 20 min; reaction conditions B: HCO2−NH4+, Pd/C 5%, conventional oil bath heating, 60 °C, 20 min. 2 Approximately 20% of the saturated ketone was obtained as a minor product. 3 The only product obtained was a saturated ketone. * In all reactions conducted under conventional thermal heating, approximately 90% of the starting material (chalcone) was recovered.
Table 3. Time and temperature effects on selectivity in nitro chalcone reduction.
Table 3. Time and temperature effects on selectivity in nitro chalcone reduction.
Organics 06 00040 i019
EntryChalconeTemp. (°C)Time (min)Major ProductYield (%)
1176020C1795 1
2176040C1755
3176060C1752
4178060C1752
5186020C1896 1
6186040C1854
7186060C1853
8188060C1851
9196020A1981
10196040A1980
11196060A1983
12198060A1985
13206020A20100
14206040A20100
15206060A20100
16208060A2098
17216020A21100
18216040A21100
19216060A21100
20218060A2197
1 No formation of the alcohol was detected.
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Silva, W.A.; Takada, S.C.S.; Nogueira, F.M.; Almeida, L.A.R. Microwave-Assisted Catalytic Transfer Hydrogenation of Chalcones: A Green, Fast, and Efficient One-Step Reduction Using Ammonium Formate and Pd/C. Organics 2025, 6, 40. https://doi.org/10.3390/org6030040

AMA Style

Silva WA, Takada SCS, Nogueira FM, Almeida LAR. Microwave-Assisted Catalytic Transfer Hydrogenation of Chalcones: A Green, Fast, and Efficient One-Step Reduction Using Ammonium Formate and Pd/C. Organics. 2025; 6(3):40. https://doi.org/10.3390/org6030040

Chicago/Turabian Style

Silva, Wender Alves, Sayuri Cristina Santos Takada, Felipe Marques Nogueira, and Luiz Arthur Ramos Almeida. 2025. "Microwave-Assisted Catalytic Transfer Hydrogenation of Chalcones: A Green, Fast, and Efficient One-Step Reduction Using Ammonium Formate and Pd/C" Organics 6, no. 3: 40. https://doi.org/10.3390/org6030040

APA Style

Silva, W. A., Takada, S. C. S., Nogueira, F. M., & Almeida, L. A. R. (2025). Microwave-Assisted Catalytic Transfer Hydrogenation of Chalcones: A Green, Fast, and Efficient One-Step Reduction Using Ammonium Formate and Pd/C. Organics, 6(3), 40. https://doi.org/10.3390/org6030040

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