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Article

Synthesis of Functionalized Azepines via Cu(I)-Catalyzed Tandem Amination/Cyclization Reaction of Fluorinated Allenynes

by
Anna N. Philippova
,
Daria V. Vorobyeva
,
Pavel S. Gribanov
,
Ivan A. Godovikov
and
Sergey N. Osipov
*
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilova str., Moscow 119991, Russia
*
Author to whom correspondence should be addressed.
Molecules 2022, 27(16), 5195; https://doi.org/10.3390/molecules27165195
Submission received: 21 July 2022 / Revised: 11 August 2022 / Accepted: 12 August 2022 / Published: 15 August 2022
(This article belongs to the Special Issue Chemistry of Nitrogen Heterocyclic Compounds)
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Abstract

:
An efficient method for the selective preparation of trifluoromethyl-substituted azepin-2-carboxylates and their phosphorous analogues has been developed via Cu(I)-catalyzed tandem amination/cyclization reaction of functionalized allenynes with primary and secondary amines.

1. Introduction

Azepane and its functionalized derivatives are important structural motifs present in variety of natural products and bioactive molecules with a wide range of medicinal and pharmaceutical properties [1,2,3,4,5,6,7,8] including antidiabetic [9,10,11], anticancer [12,13,14], and antiviral [15,16,17] activities, thus attracting a significant interest of the researchers in a new lead compound discovery. The most cited example of a natural product containing an azepane core is the fungal metabolite protein kinase inhibitor Balanol [18]. Additional examples of bioactive synthetic azepane-based compounds are depicted on Figure 1. Despite remarkable efforts being made to develop efficient synthetic methods for these seven-membered azacycles [19,20,21,22,23,24,25,26,27,28,29,30,31], slow cyclization kinetics have hindered the development of robust methods for the direct construction of these medium-ring heterocyclic systems [32]. Therefore, the development of new effective strategies for the selective preparation of azepane derivatives with unique substitution patterns is of great interest.
On the other hand, organofluorine compounds are currently finding increasingly important applications in modern pharma, crop protection, and materials science [33,34,35,36,37,38]. This fact stimulates synthetic chemists to develop new efficient methodologies for the selective introduction of fluorine and fluorinated groups into different organic molecules. In this context, fluorine-containing amino acids, especially their constrained cyclic derivatives, attract a considerable interest as crucial targets in bioorganic and medicinal chemistry for the design of potent and highly selective bioactive compounds [38,39,40,41].
Recently, we have developed a convenient one-step protocol for the preparation of functionalized allenes based on [2,3]-sigmatropic rearrangement of propargyl-containing nitrogen ylides generated in situ from α-CF3-diazo compounds 1 (Scheme 1A) [42]. The synthetic potential of 2 has been clearly revealed in their intermolecular transformation under transition metal catalysis such as Cu(I)-catalyzed hydroamination [43] and Ru(II)-catalyzed dimerization (Scheme 1B) [44]. In addition, allenynes 2 [R = −(CH2)nC≡CH] have proved to be unique doubly unsaturated synthons to afford the bicyclic amino acid derivatives via intramolecular Pauson–Khand [42] and [2+2]-cycloaddition [45,46] reactions (Scheme 1C).
According to our long-term program on the study of transition metal-catalyzed reactions of unsaturated α-amino acid derivatives [47,48,49,50,51,52,53,54], now we want to disclose an efficient approach to novel α-CF3-containing azepine-2-carboxylates and their phosphorous analogues via a new type of catalytic allenyne transformation involved the combination of intermolecular amine addition with intramolecular cyclization (Scheme 1D). To the best of our knowledge, this reaction constitutes the first example of tandem amination/cyclization of allenynes under metal-catalysis.

2. Results and Discussion

Given our recent finding that an allene system is readily capable of undergoing the selective hydroamination with secondary and primary amines in the presence of copper catalysts [41], we were curious to investigate what will happen with allenyne bearing propargyl group with acidic proton on terminal triple bond under the similar catalytic conditions. To answer this question, we began our study by testing the reaction between allenyne 2a and aniline. Cationic Cu(I) complex Cu(MeCN)4PF6 was chosen as the most competent catalyst for allene hydroamination process. Anhydrous THF, toluene, 1,2-dichloroethane (DCE), and 1,4-dioxane were employed as the solvents. As a result, the reaction was found to smoothly proceed in the presence of 10 mol% Cu(MeCN)4PF6 and 2.0 equiv. of aniline in dioxane at 90 °C for 8 h to give an unusual azepine derivative 3a in 65% NMR yield (Table 1, entry 1).
A prolonged reaction did not lead to a better yield of the product, while causing the formation of a small number of impurities (measured by 19F NMR spectroscopy). The subsequent decrease of the catalyst loading to 5 mol% resulted in a notably lower conversion of 2a affording 3a in 35% yield (entry 3) along with significant amounts of starting materials. At the same time, the decline of amine amount and reaction temperature have improved the yield of the desired product 3a (entry 4). Copper(I) salts (CuCl or CuI) have proved to be inactive for the process (entries 8 and 9). Finally, the optimum conditions include the heating of a mixture of allenyne 2a and 1.2 equiv. aniline in the presence of 10 mol% of catalyst in dioxane at 70 °C for 6 h (entry 10).
With the optimized conditions in hand, we examined a series of primary and secondary amines (such as substituted anilines, morpholine, and piperidine) as substrates for this catalytic transformation. As a result, we found that the reaction proceeded smoothly with all tested substrates furnishing the corresponding CF3-containing azepine-2-carboxylate derivatives 3a–j in moderate to good yields (Scheme 2). However, the only limitation was found for primary aliphatic amines, such as iso-propyl and butyl amine; all our attempts to initiate their reactions with allenyne 2a failed.
The characterization of the compounds obtained was performed using standard physicochemical methods (NMR spectroscopy and high-resolution mass spectrometry). The location of exo- and endocyclic double bonds inherent to the seven-membered azepine structure 3 was determined using 2D NMR spectroscopy. Thus, characteristic cross-peaks are observed in the spectrum between protons of the terminal =CH2 group at position 8 and protons of neighboring CH2 groups at positions 3 and 5 (both are spin AB-systems), unambiguously indicating their spatial proximity (Figure 2).
A feasible mechanism of this tandem transformation may involve the initial formation of copper acetylide as a key step, which is similar to the well-established Cu(I)-catalyzed click reaction [55,56], due to higher acidity of acetylene proton. Then, apparently, nucleophilic addition of the amine to acetylide occurs according to its inherent polarity, followed by intramolecular cyclization at the central carbon atom of the pre-activated allene system to afford the seven-membered product after typical skeleton reorganization (Scheme 3). More detailed mechanistic study of this unprecedented reaction is currently in progress.
Taking into account that α-amino phosphonates are the structural mimics of α-amino acids exhibiting a broad spectrum of remarkable biological properties including antibacterial, antiviral, anticancer, and some other types of bioactivity [57,58,59,60,61,62,63], we checked the reactivity of phosphonate-containing allenyne 2b in the amination/cyclization reaction with amines under the found catalytic conditions. It turned out that 2b has demonstrated comparable to carboxylate analogue 2a reactivity towards primary and secondary amines yielding the corresponding trifluoromethylated azepine-2-phosphonates 4a–e in moderate to good yields (Scheme 4).
In general, the NMR yields of 4 exceeded 80% (determined by 19F NMR spectroscopy) in all studied reactions; however, moderate yields in some cases were caused by purification to obtain analytically pure samples using column chromatography followed by re-crystallization.

3. Materials and Methods

3.1. General Information

All solvents used in the reactions were freshly distilled from appropriate drying agents before use. All reagents were used as purchased from Sigma-Aldrich (Munich, Germany). Analytical TLC was performed with Merck silica gel 60 F254 plates (Darmstadt, Germany); visualization was accomplished with UV light, iodine vapors, or by spraying with Ce(SO4)2 solution in 5% H2SO4. Chromatography was carried out using Merck silica gel (Kieselgel 60, 0.063–0.200 mm, Darmstadt, Germany) and petroleum ether/ethyl acetate, ethyl acetate, ethyl acetate/methanol as an eluent. NMR spectra were obtained with Bruker AV-300 (19F, 31P) and AV-400 (1H, 13C, 19F, 31P) spectrometers (Karlsruhe, Germany) operating at 400 MHz for 1H (TMS reference), at 101 MHz for 13C, 282 and at 376 MHz for 19F (CCl3F reference), and at 121 MHz for 31P (H3PO4 reference). High-Resolution Mass Spectrometry spectra were carried out using AB Sciex TripleTOF 5600+ (Framingham, MA, USA) supported different ionization sources. The starting allenynes 2a,b were synthesized via the previously described protocol [42].

3.2. General Procedure

A mixture of amine (0.485 mmol), allenyne (0.404 mmol), and [Cu(CH3CN)4PF6] (10 mol%) in anhydrous 1,4-dioxane (3 mL) was stirred under argon at 70 °C for 6–16 h. Then, the reaction mixture was cooled to room temperature, solvent was removed under reduced pressure, and the residue was subjected to column chromatography on silica gel (petroleum ether/ethyl acetate or ethyl acetate/methanol for phosphonate derivatives) to yield the purified product (See Supplementary Materials).
  • Methyl 1-methyl-4-methylene-6-(phenylamino)-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3a)
Molecules 27 05195 i002
Yield: 65% as a light brown solid. 1H NMR (400 MHz, CDCl3) δ 7.17 (t, J = 7.9 Hz, 2H), 6.72 (t, J = 7.3 Hz, 1H), 6.57 (d, J = 7.8 Hz, 2H), 5.81 (s, 1H), 5.24 (s, 1H), 5.11 (s, 1H), 4.03 (d, J = 3.7 Hz, 2H), 3.93 (s, 1H), 3.74 (s, 3H), 3.63 (d, J = 13.7 Hz, 1H), 3.55 (d, J = 13.6 Hz, 1H), 2.57 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.4, 147.7, 137.2, 137.1, 129.2, 124.8 (q, J = 290.8, 276.5 Hz), 118.9, 117.9, 113.0, 111.0, 70.4 (q, J = 25.0 Hz), 55.1, 52.8, 45.2, 40.2. 19F NMR (376 MHz, CDCl3) δ −68.30. HRMS (ESI) calcd. for C17H20F3N2O2 [M + H]+: 341.1471, found: 341.1472.
  • Methyl 1-methyl-4-methylene-6-(p-tolylamino)-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3b)
Molecules 27 05195 i003
Yield: 61% as a light brown solid. 1H NMR (400 MHz, CDCl3) δ 6.97 (d, J = 8.1 Hz, 2H), 6.49 (d, J = 8.2 Hz, 2H), 5.81 (s, 1H), 5.23 (s, 1H), 5.10 (s, 1H), 4.06–3.95 (m, 2H), 3.79 (s, 1H), 3.75 (s, 3H), 3.65–3.50 (m, 3H), 2.56 (s, 3H), 2.24 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.5, 145.5, 137.4, 137.2, 129.7, 127.1, 124.9 (q, J = 290.7 Hz), 113.1, 111.0, 70.4 (d, J = 25.5 Hz), 55.1, 52.8, 45.7, 40.3, 20.5. 19F NMR (376 MHz, CDCl3) δ −68.33. HRMS (ESI) calcd. for C18H22F3N2O2 [M + H]+: 355.1628, found: 355.1628.
  • Methyl 6-(4-methoxyphenylamino)-1-methyl-4-methylene-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3c)
Molecules 27 05195 i004
Yield: 59% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 6.75 (d, J = 8.3 Hz, 2H), 6.52 (d, J = 8.4 Hz, 2H), 5.80 (s, 1H), 5.22 (s, 1H), 5.09 (s, 1H), 4.02–3.92 (m, 2H), 3.74 (s, 6H), 3.61 (d, J = 13.6 Hz, 1H), 3.52 (d, J = 13.5 Hz, 1H), 2.55 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.4, 152.4, 142.0, 137.4, 137.2, 124.9 (q, J = 290.5 Hz), 118.8, 114.8, 114.2, 110.9, 70.4 (q, J = 24.9 Hz), 55.8, 55.0, 52.7, 46.1, 40.2. 19F NMR (376 MHz, CDCl3) δ −68.33. HRMS (ESI) calcd. for C18H22F3N2O3 [M + H]+: 371.1577, found: 371.1579.
  • Methyl 1-methyl-4-methylene-6-(o-tolylamino)-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3d)
Molecules 27 05195 i005
Yield: 40% as a light brown solid. 1H NMR (400 MHz, CDCl3) δ 7.11–7.04 (m, 2H), 6.70–6.64 (m, 1H), 6.46 (d, J = 7.9 Hz, 1H), 5.77 (s, 1H), 5.27 (s, 1H), 5.13 (s, 1H), 4.14–4.04 (m, 2H), 3.82 (s, 1H), 3.74 (s, 3H), 3.64 (d, J = 13.7 Hz, 1H), 3.56 (d, J = 13.6 Hz, 1H), 2.57 (s, 3H), 2.17 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.4, 145.6, 137.2, 137.2, 130.1, 127.1, 124.9 (q, J = 290.9 Hz), 121.9, 118.9, 117.5, 111.0, 110.3, 70.9–69.9 (m), 55.1, 52.8, 45.3, 40.2, 17.6. 19F NMR (376 MHz, CDCl3) δ −68.32. HRMS (ESI) calcd. for C18H22F3N2O2 [M + H]+: 355.1628, found: 355.1629.
  • Methyl 1-methyl-4-methylene-6-(m-tolylamino)-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3e)
Molecules 27 05195 i006
Yield: 63% as a thick light brown oil. 1H NMR (400 MHz, CDCl3) δ 7.1 (t, J = 7.5 Hz, 1H), 6.5 (d, J = 7.0 Hz, 1H), 6.4–6.4 (m, 2H), 5.8 (s, 1H), 5.2 (s, 1H), 5.1 (s, 1H), 4.1–4.0 (m, 2H), 3.8 (s, 3H), 3.6 (d, J = 13.7 Hz, 1H), 3.5 (d, J = 13.6 Hz, 1H), 2.6 (s, 3H), 2.3 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.4, 147.8, 139.0, 137.2, 137.2, 129.1, 124.9 (q, J = 290.5 Hz), 118.9–118.9 (m), 118.8, 113.7, 111.0, 110.2, 70.4 (q, J = 25.2 Hz), 55.1, 52.7, 45.4, 40.2, 21.7. 19F NMR (376 MHz, CDCl3) δ −68.4. HRMS (ESI) calcd. for C18H22F3N2O2 [M + H]+: 355.1628, found: 355.1628.
  • Methyl 6-(3-methoxyphenylamino)-1-methyl-4-methylene-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3f)
Molecules 27 05195 i007
Yield: 58% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 7.06 (t, J = 8.1 Hz, 1H), 6.29 (d, J = 7.9 Hz, 1H), 6.19 (d, J = 8.0 Hz, 1H), 6.11 (s, 1H), 5.80 (s, 1H), 5.22 (s, 1H), 5.10 (s, 1H), 4.08–3.94 (m, 2H), 3.75 (s, 6H), 3.61 (d, J = 13.7 Hz, 1H), 3.53 (d, J = 13.5 Hz, 1H), 2.56 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.4, 160.9, 149.2, 137.2, 137.1, 130.0, 124.9 (q, J = 290.5 Hz), 118.9, 111.0, 106.1, 103.1, 99.0, 70.4 (q, J = 25.3 Hz), 55.1, 55.1, 52.7, 45.3, 40.2. 19F NMR (376 MHz, CDCl3) δ −68.42. HRMS (ESI) calcd. for C18H22F3N2O3 [M + H]+: 371.1577, found: 371.1578.
  • Methyl 6-(2,4-dimethylphenylamino)-1-methyl-4-methylene-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3g)
Molecules 27 05195 i008
Yield: 50% as a thick light brown oil. 1H NMR (400 MHz, CDCl3) δ 6.97–6.83 (m, 1H), 6.39 (d, J = 7.9 Hz, 1H), 5.79 (s, 1H), 5.27 (s, 1H), 5.12 (s, 1H), 4.13–3.97 (m, 1H), 3.75 (s, 2H), 3.64 (d, J = 13.7 Hz, 1H), 3.55 (d, J = 13.3 Hz, 1H), 2.57 (s, 2H), 2.23 (s, 2H), 2.15 (s, 2H). 13C NMR (101 MHz, CDCl3) δ 167.4, 143.4, 137.4, 137.2, 131.0, 127.4, 126.6, 124.9 (q, J = 290.7 Hz), 122.1, 118.9, 111.0, 110.5, 70.4 (q, J = 25.8 Hz), 55.1, 52.7, 45.7, 40.2, 20.4, 17.5. 19F NMR (376 MHz, CDCl3) δ −68.32. HRMS (ESI) calcd. for C19H24F3N2O2 [M + H]+: 369.1784, found: 369.1789.
  • Methyl 6-(4-fluorophenylamino)-1-methyl-4-methylene-2-(trifluoromethyl)-2,3,4,5-tetrahydro-1H-azepine-2-carboxylate (3h)
Molecules 27 05195 i009
Yield: 62% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 6.87 (t, J = 8.7 Hz, 2H), 6.54–6.46 (m, 2H), 5.77 (s, 1H), 5.22 (s, 1H), 5.11 (s, 1H), 4.07–3.92 (m, 2H), 3.74 (s, 3H), 3.64–3.48 (m, 2H), 2.55 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.4, 157.3, 155.0, 143.9, 137.2, 136.9, 124.9 (q, J = 290.6 Hz), 119.0, 115.8, 115.6, 113.9, 113.8, 111.0, 70.4 (q, J = 25.1, 24.6 Hz), 55.1, 52.8, 45.8, 40.3. 19F NMR (376 MHz, CDCl3) δ −68.35, −127.72. HRMS (ESI) calcd. for C17H19F4N2O2 [M + H]+: 359.1377, found: 359.1377.
  • Methyl 1-methyl-4-methylene-2-(trifluoromethyl)-6-(3-(trifluoromethyl)phenylamino)-2,3,4,5-tetrahydro-1H-azepine-2-carboxylate (3i)
Molecules 27 05195 i010
Yield: 48% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 7.25–7.22 (m, 1H), 6.95 (d, J = 7.8 Hz, 1H), 6.77–6.68 (m, 2H), 5.76 (s, 1H), 5.23 (s, 1H), 5.13 (s, 1H), 4.14–3.98 (m, 2H), 3.73 (s, 3H), 3.65–3.49 (m, 2H), 2.55 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.4, 147.8, 137.0, 136.4, 129.7, 127.1 (d, J = 272.8 Hz), 124.8 (q, J = 290.7 Hz), 119.0, 116.2, 114.4 (d, J = 3.9 Hz), 111.2, 109.0 (d, J = 3.9 Hz), 70.4 (q, J = 25.4, 25.0 Hz), 55.1, 52.8, 45.0, 40.3, 29.8. 19F NMR (376 MHz, CDCl3) δ −62.92, −68.60. HRMS (ESI) calcd. for C18H19F6N2O2 [M + H]+: 409.1345, found: 409.1344.
  • Methyl 1-methyl-4-methylene-6-(piperidin-1-yl)-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3j)
Molecules 27 05195 i011
Yield: 55% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 5.78 (s, 1H), 5.42 (s, 1H), 5.04 (s, 1H), 3.81 (s, 3H), 3.57 (d, J = 14.1 Hz, 1H), 3.47 (d, J = 13.9 Hz, 1H), 3.11 (q, J = 9.2 Hz, 2H), 2.54 (s, 3H), 2.33 (s, 4H), 1.57–1.51 (m, 4H), 1.41 (s, 2H). 13C NMR (101 MHz, CDCl3) δ 167.7, 137.7, 137.4, 125.0 (q, J = 290.4 Hz), 119.7, 111.8, 60.3, 55.3, 54.8, 52.7, 40.3, 26.1, 24.5. 19F NMR (376 MHz, CDCl3) δ −68.73. HRMS (ESI) calcd. for C16H24F3N2O2 [M + H]+: 333.1784, found: 333.1786.
  • Methyl 1-methyl-4-methylene-6-morpholino-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3k)
Molecules 27 05195 i012
Yield: 62% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 5.77 (s, 1H), 5.44 (s, 1H), 5.06 (s, 1H), 3.80 (s, 3H), 3.69–3.65 (m, 4H), 3.56 (d, J = 13.6 Hz, 1H), 3.45 (d, J = 13.5 Hz, 1H), 3.13 (q, 2H), 2.52 (s, 3H), 2.42–2.36 (m, 4H). 13C NMR (101 MHz, CDCl3) δ 167.5, 137.4, 136.7, 129.7–120.5 (m), 120.3, 112.1, 70.4 (q, J = 25.2 Hz), 67.1, 60.2, 55.2, 53.7, 52.8, 40.3. 19F NMR (376 MHz, CDCl3) δ −68.76. HRMS (ESI) calcd. for C15H22F3N2O3 [M + H]+: 335.1577, found: 335.1583.
  • Methyl 6-(dibenzylamino)-1-methyl-4-methylene-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepine-2-carboxylate (3l)
Molecules 27 05195 i013
Yield: 30% as thick yellow oil. 1H NMR (400 MHz, CDCl3) δ 7.35–7.28 (m, 8H), 7.26–7.21 (m, 2H), 6.05 (s, 1H), 5.28 (s, 1H), 5.03 (s, 1H), 3.76 (s, 3H), 3.56–3.49 (m, 5H), 3.45 (d, J = 13.5 Hz, 1H), 3.24 (s, 2H), 2.53 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 167.7, 139.2, 138.2, 137.4, 129.0, 128.4, 127.1, 123.5 (t, J = 290.0 Hz), 120.1, 112.1, 70.5 (d, J = 25.2 Hz), 58.4, 55.4, 55.2, 52.7, 40.3. 19F NMR (376 MHz, CDCl3) δ −68.73. HRMS (ESI) calcd. for C25H28F3N2O2 [M + H]+: 445.2097, found: 445.2092.
  • Diethyl 1-methyl-4-methylene-6-(phenylamino)-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepin-2-ylphosphonate (4a)
Molecules 27 05195 i014
Yield: 45% as a yellow solid. 1H NMR (400 MHz, CDCl3) δ 7.15 (t, J = 7.8 Hz, 2H), 6.70 (t, J = 7.3 Hz, 1H), 6.58 (d, J = 7.8 Hz, 2H), 5.89 (d, J = 5.3 Hz, 1H), 5.19 (s, 1H), 5.04 (s, 1H), 4.13 – 3.99 (m, 6H), 3.48 (s, 2H), 2.85 (s, 3H), 1.24–1.16 (m, 6H). 13C NMR (101 MHz, CDCl3) δ 147.8, 137.7 (d, J = 3.4 Hz), 136.9 (d, J = 9.9 Hz), 129.2, 129.7–120.6 (m), 119.1–118.8 (m), 117.8, 113.0, 110.2 (d, J = 2.2 Hz), 64.6 (d, J = 7.3 Hz), 62.9 (d, J = 8.0 Hz), 55.3 (d, J = 7.4 Hz), 45.4 (d, J = 1.9 Hz), 41.0, 16.5 (d, J = 5.9 Hz), 16.3 (d, J = 6.0 Hz). 19F NMR (376 MHz, CDCl3) δ −64.56 (d, J = 6.5 Hz). 31P NMR (121 MHz, CDCl3) δ 14.5 (q, J = 6.8 Hz). HRMS (ESI) calcd. for C19H27F3N2O3P [M + H]+: 419.1706, found: 419.1709.
  • Diethyl 1-methyl-4-methylene-6-(p-tolylamino)-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepin-2-ylphosphonate (4b)
Molecules 27 05195 i015
Yield: 61% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 6.97 (d, J = 7.9 Hz, 2H), 6.52 (d, J = 7.6 Hz, 2H), 5.94–5.84 (m, 1H), 5.20 (s, 1H), 5.04 (s, 1H), 4.14–3.97 (m, 6H), 3.48 (s, 2H), 2.85 (s, 3H), 2.22 (s, 3H), 1.25–1.16 (m, 6H). 13C NMR (101 MHz, CDCl3) δ 145.5, 137.7 (d, J = 3.3 Hz), 137.2 (d, J = 9.7 Hz), 129.7, 127.0, 125.2 (dd, J = 292.9, 12.6 Hz). 119.0 (d, J = 7.7 Hz), 113.2, 110.2, 64.6 (d, J = 7.3 Hz), 63.0 (d, J = 8.0 Hz), 55.3 (d, J = 7.3 Hz), 45.8, 41.0, 20.5, 16.8–15.6 (m). 19F NMR (376 MHz, CDCl3) δ −64.57 (d, J = 6.3 Hz). 31P NMR (121 MHz, CDCl3) δ 14.5 (q, J = 7.2 Hz). HRMS (ESI) calcd. for C20H29F3N2O3P [M + H]+: 433.1862, found: 433.1862.
  • Diethyl 6-(4-methoxyphenylamino)-1-methyl-4-methylene-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepin-2-ylphosphonate (4c)
Molecules 27 05195 i016
Yield: 43% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 6.75 (d, J = 8.8 Hz, 2H), 6.55 (d, J = 8.7 Hz, 2H), 5.90 (d, J = 5.3 Hz, 1H), 5.19 (s, 1H), 5.03 (s, 1H), 4.15–4.01 (m, 4H), 3.98 (s, 2H), 3.73 (s, 3H), 3.47 (s, 2H), 2.85 (s, 3H), 1.24–1.19 (m, 6H). 13C NMR (101 MHz, CDCl3) δ 152.4, 142.1, 137.8 (d, J = 3.3 Hz), 137.3 (d, J = 9.8 Hz), 125.2 (dd, J = 293.1, 12.8 Hz), 118.9 (d, J = 10.3 Hz), 114.9, 114.3, 110.2, 64.6 (d, J = 7.2 Hz), 63.0 (d, J = 7.8 Hz), 55.4 (d, J = 7.3 Hz), 46.3, 41.0, 29.8, 16.4 (dd, J = 21.8, 5.8 Hz). 19F NMR (376 MHz, CDCl3) δ −64.57 (d, J = 6.7 Hz). 31P NMR (121 MHz, CDCl3) δ 14.6 (q, J = 7.1 Hz). HRMS (ESI) calcd. for C20H29F3N2O4P [M + H]+: 449.1812, found: 449.1813.
  • Diethyl 1-methyl-4-methylene-6-(piperidin-1-yl)-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepin-2-ylphosphonate (4d)
Molecules 27 05195 i017
Yield: 46% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 6.00–5.96 (m, 1H), 5.40 (s, 1H), 5.06 (s, 1H), 4.21–4.15 (m, 4H), 3.50–3.36 (m, 4H), 2.83 (s, 3H), 2.67–2.55 (m, 4H), 1.66 (p, J = 5.7 Hz, 4H), 1.52–1.44 (m, 2H), 1.33 (t, J = 7.1 Hz, 3H), 1.28–1.22 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 137.7 (d, J = 3.7 Hz), 135.1–134.8 (m), 125.2 (d, J = 280.8 Hz), 122.7–122.3 (m), 112.0, 64.8 (d, J = 7.7 Hz), 63.4 (d, J = 7.7 Hz), 59.5, 55.2 (d, J = 7.7 Hz), 54.5, 40.9, 25.1, 23.6, 16.5 (dd, J = 5.7, 3.5 Hz). 19F NMR (282 MHz, C6D6) δ −63.08 (d, J = 7.7 Hz). 31P NMR (121 MHz, CDCl3) δ 14.84 (q, J = 7.3 Hz). HRMS (ESI) calcd. for C18H31F3N2O3P [M + H]+: 411.2019, found: 411.2024.
  • Diethyl 1-methyl-4-methylene-6-morpholino-2-(trifluoromethyl)-2,3,4,7-tetrahydro-1H-azepin-2-ylphosphonate (4e)
Molecules 27 05195 i018
Yield: 62% as a thick brown oil. 1H NMR (400 MHz, CDCl3) δ 5.91–5.81 (m, 1H), 5.39 (s, 1H), 4.99 (s, 1H), 4.20–4.10 (m, 4H), 3.69–3.65 (m, 4H), 3.45 (d, J = 13.6 Hz, 1H), 3.37 (d, J = 13.2 Hz, 1H), 3.15 (d, J = 2.7 Hz, 2H), 2.82 (s, 3H), 2.41 (s, 4H), 1.31 (t, J = 7.1 Hz, 3H), 1.21 (t, J = 7.1 Hz, 3H). 13C NMR (101 MHz, CDCl3) δ 137.9 (d, J = 3.4 Hz), 136.2 (d, J = 9.9 Hz), 125.3 (qd, J = 293.4, 13.2 Hz), 120.7–120.3 (m), 111.2 (d, J = 2.1 Hz), 67.1, 64.7 (d, J = 7.2 Hz), 63.0 (d, J = 7.7 Hz), 60.6–60.5 (m), 55.3 (d, J = 8.0 Hz), 53.7, 40.9, 16.5 (dd, J = 5.7, 2.0 Hz). 19F NMR (376 MHz, CDCl3) δ −64.24 (d, J = 7.4 Hz). 31P NMR (121 MHz, CDCl3) δ 14.6. HRMS (ESI) calcd. for C17H29F3N2O4P [M + H]+: 413.1812, found: 413.1819.

4. Conclusions

In conclusion, we have elaborated an effective protocol for the preparation of novel CF3-containing azepin-2-carboxylate and azepin-2-phosphonate derivatives. The method is based on a new type of tandem transformation of functionalized allenynes under copper(I) catalysis, which includes a combination of intermolecular addition of an amine to a copper-activated triple bond followed by intramolecular cyclization along the allenyl group. The reactions can be readily accomplished in dioxane within a few hours at 70 °C in the presence of complex Cu(MeCN)4PF6 (10 mol%) providing access to a new family of functionally substituted seven-membered azacycles.

Supplementary Materials

The following are available online: https://www.mdpi.com/article/10.3390/molecules27165195/s1, copies of 1H, 13C NMR and HRMS spectra for all novel compounds.

Author Contributions

Conceptualization, S.N.O.; methodology, S.N.O.; investigation, A.N.P., D.V.V., P.S.G., I.A.G. (synthesis, NMR spectra registering, and characterization), A.N.P., D.V.V. (synthesis); writing—original draft preparation, S.N.O., A.N.P.; writing—review and editing, P.S.G., S.N.O.; supervision, S.N.O.; project administration, S.N.O.; funding acquisition, S.N.O. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the Russian Foundation of Basic Research (grant RFBR No. 20-03-00481).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Acknowledgments

NMR studies and spectral characterization were performed with financial support from the Ministry of Science and Higher Education of the Russian Federation using the equipment of the Center for Molecular Composition Studies of INEOS RAS.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Samples of all of the compounds are available from the authors.

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Molecules 27 05195 g001 550
Figure 1. Bioactive molecules containing azepane rings.
Figure 1. Bioactive molecules containing azepane rings.
Molecules 27 05195 g001
Molecules 27 05195 sch001 550
Scheme 1. Previous and present work.
Scheme 1. Previous and present work.
Molecules 27 05195 sch001
Molecules 27 05195 sch002 550
Scheme 2. Synthesis of trifluoromethylated azepine-2-carboxylates 3.
Scheme 2. Synthesis of trifluoromethylated azepine-2-carboxylates 3.
Molecules 27 05195 sch002
Molecules 27 05195 g002 550
Figure 2. A fragment of 2D 1H ROESY NMR spectrum (500 MHz, CDCl3) of 3d.
Figure 2. A fragment of 2D 1H ROESY NMR spectrum (500 MHz, CDCl3) of 3d.
Molecules 27 05195 g002
Molecules 27 05195 sch003 550
Scheme 3. Possible reaction pathway to functional azepines.
Scheme 3. Possible reaction pathway to functional azepines.
Molecules 27 05195 sch003
Molecules 27 05195 sch004 550
Scheme 4. Synthesis of trifluoromethylated azepine-2-phosphonates 4.
Scheme 4. Synthesis of trifluoromethylated azepine-2-phosphonates 4.
Molecules 27 05195 sch004
Table
Table 1. Optimization of amination/cyclization of allenyne 2a with aniline 1.
Table 1. Optimization of amination/cyclization of allenyne 2a with aniline 1.
Molecules 27 05195 i001
EntryAmine (Equiv.)Catalyst (mol%)Solv./Temp. (°C)Time (h)Yield 2 (%)
12.0Cu(MeCN)4PF6 (10)dioxane/90865 (43 3)
22.0Cu(MeCN)4PF6 (10)dioxane/901660
32.0Cu(MeCN)4PF6 (5)dioxane/90835
41.5Cu(MeCN)4PF6 (10)dioxane/80877
51.5Cu(MeCN)4PF6 (10)DCE/801635
61.5Cu(MeCN)4PF6 (10)toluene/801643
71.5Cu(MeCN)4PF6 (10)THF/701675
82.0CuI (10)dioxane/908NR
92.0CuCl (10)dioxane/908NR
101.2Cu(MeCN)4PF6 (10)dioxane/70691 (65 3)
112.0-dioxane/9016NR
1Reagents and conditions: Allenyne 2a (0.2 mmol), solvent (3 mL). 2 Determined by 19F NMR spectroscopy. 3 Isolated yield.
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Philippova, A.N.; Vorobyeva, D.V.; Gribanov, P.S.; Godovikov, I.A.; Osipov, S.N. Synthesis of Functionalized Azepines via Cu(I)-Catalyzed Tandem Amination/Cyclization Reaction of Fluorinated Allenynes. Molecules 2022, 27, 5195. https://doi.org/10.3390/molecules27165195

AMA Style

Philippova AN, Vorobyeva DV, Gribanov PS, Godovikov IA, Osipov SN. Synthesis of Functionalized Azepines via Cu(I)-Catalyzed Tandem Amination/Cyclization Reaction of Fluorinated Allenynes. Molecules. 2022; 27(16):5195. https://doi.org/10.3390/molecules27165195

Chicago/Turabian Style

Philippova, Anna N., Daria V. Vorobyeva, Pavel S. Gribanov, Ivan A. Godovikov, and Sergey N. Osipov. 2022. "Synthesis of Functionalized Azepines via Cu(I)-Catalyzed Tandem Amination/Cyclization Reaction of Fluorinated Allenynes" Molecules 27, no. 16: 5195. https://doi.org/10.3390/molecules27165195

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