A Straightforward and Efficient Approach to the Synthesis of 3-Cyano-Coumarine Derivatives ^†

Abstract

Oxygen heterocycles represent a significant category of organic molecules that are abundant in nature and important in scientific research due to their use in diverse applications across various fields. Coumarins, in particular, comprise a wide range of compounds known for their extensive biological activities, making them invaluable in medicine, pharmacology, cosmetics, and the food industry. The biological effects and potential applications of coumarins are closely tied to their specific chemical structures. As a result, researchers frequently engage in the synthesis of coumarin derivatives to explore their varied uses. In this context, we focused on the synthesis of 3-cyano-coumarin and its derivatives. This study introduces a simple synthesis method that enables the efficient and accessible production of these structures under mild, environmentally friendly conditions, yielding excellent results.

1. Introduction

Heterocyclic compounds constitute the largest and most diverse group of organic compounds. Their numbers are growing rapidly due to ongoing research and advancements in synthesis technique [1,2]. These compounds are significant across various scientific disciplines, including medicinal chemistry and biochemistry. A number of heterocyclic compounds are currently known [3,4], mainly oxygen heterocyclic compounds [5,6], which are a vital class of organic molecules found abundantly in nature and important in scientific research due to their diverse applications across multiple fields [7]. Extensive research has focused on the development of new molecular composite materials and numerous organic synthesis protocols that have a wide range of applications in the chemical sciences [8,9]. Numerous oxygen heterocyclic compounds found in nature possess both physiological and pharmacological properties, and they are integral to many important biological molecules [10,11], particularly coumarins [12].

Coumarins comprise a diverse range of compounds recognized for their wide spectrum of biological activities, including antioxidant, anticonvulsant, antitumor, anti-inflammatory, and antimicrobial properties [13,14]. This makes them invaluable in fields such as medicine, pharmacology, cosmetics, and the food industry. The biological effects and potential applications of coumarins are closely tied to their unique chemical structures. The broad range of applications and growing interest in coumarins as a key heterocycle have motivated us to explore recent advancements in their synthesis [15,16].

In this context, we are interested in the synthesis of 3-cyano-coumarin and its derivatives (Figure 1). This study introduces a simple synthesis method that enables the efficient and accessible production of these structures under mild, environmentally friendly conditions, achieving excellent yields.

Figure 1. The general structure of 3-cyano-coumarin derivatives.

2. Results and Discussion

In this work, we report the two-step synthesis of 3-cyano-coumarin derivatives, outlined as follows.

2.1. Alkenes Synthesis 3a–e

The initial step in our synthetic approach is the synthesis of various alkenes (3a–e). By reacting substituted aromatic aldehydes (1a–e) with methyl cyanoacetate (2) and stirring the mixture at room temperature for 30 to 60 min, we obtained the desired products in good yields (Table 1).

Table 1. Synthesis of alkenes.

Entry	R	Yield (%)
3a	H	33
3b	4-Cl	73
3c	4-F	79
3d	3-CH3	59
3e	3,4,5 tri-OMe	90

The structure of the synthesized compounds 3a–e was confirmed by spectral analysis; the IR spectra (KBr, ν, cm⁻¹) showed the appearance of (CN) at 2215–2222 cm⁻¹, (C=C) at 1575–1603 cm⁻¹, and (C=O) at 1719–1736 cm⁻¹; and the ¹H NMR (CDCl₃, δ, ppm) showed the appearance of C-H stretch at 8.16–8.80 ppm, CH₃ stretch at 2.45 ppm, H_Ar at 7.16–7.97 ppm, and finally O-CH3 stretch at 3.85–4.04 ppm.

2.2. Synthesis of 3-Cyano-Coumarin Derivatives 5a–e

We synthesized a series of 3-cyano-coumarin derivatives (5a–e) using the previously synthesized alkynes (3a–e) in combination with resorcinol (4). This reaction was conducted at reflux with K₂CO₃ as the catalyst and ethanol as the solvent for 15 to 30 min. This strategy resulted in the formation of 3-cyano-coumarin derivatives in excellent yields (Table 2).

Table 2. Synthesis of 3-cyano-coumarin derivatives.

Entry	R	Yield (%)
3a	H	71
3b	4-Cl	88
3c	4-F	69
3d	3-CH3	73
3e	3,4,5 tri-OMe	77

The synthesized compounds 5a–e were confirmed by spectroscopic analysis; the IR spectra (KBr, ν, cm⁻¹) showed the appearance of (CN) at 2202–2208 cm⁻¹, (C=O) at 1683–1684 cm⁻¹, and (OH) at 3218–3234.

3. Experimental Procedures

3.1. General Synthesis of Alkyne Derivatives 3a–e

An equimolar mixture of methyl cyanoacetate (0.02 mol) was prepared with different derivatives of aromatic aldehydes (0.02 mol) in the presence of 5 mL EtOH as the solvent and a catalytic amount of NH₄OAc at room temperature for 30 to 60 min; the progress of the reaction was monitored by TLC and the solid formed was washed and filtered with diethyl ether and several drops of ethanol to afford the desired product in good yields (33–90%).

3.2. General Synthesis of 3-Cyano-Coumarin Derivatives 5a–e

Products (5a–e) were prepared using (0.02 mol) of Alkynes 3a–e with (0.02 mol) of resorcinol 4 in the presence of a catalytic amount of K₂CO₃ and about 5 mL of ethanol as a solvent; the reaction mixture was stirred and refluxed at 60 °C for 15 to 30 min according to TLC, and the formed solid after cooling was collected by filtration and washed with diethyl ether and ethanol. The required products were obtained with excellent yields (69–88%).

4. Conclusions

We have successfully developed a simple, rapid, and efficient synthesis route for 3-cyano-coumarin derivatives. This process offers several advantages, including a mild reaction condition, straightforward reactants, and excellent yields.