A facile synthesis of 2H-chromen-2-ones via Pechmann condensation under solvent free conditions using grinding technique

Abstract

A simple and highly efficient procedure for the synthesis of 2 H -chromen-2-ones via von Pechmann condensation, involving the grinding of different phenols and β -ketoesters in the presence of silica supported sulfuric acid at room temperature, under solvent free conditions, has been described.

A Simple and Effective Protocol for the Pechmann Reaction to Obtain 4-Methylcoumarin Derivatives Using a High-Speed Mixer Ball Mill Process

“…To evaluate its scope, other substituted phenols 1b-e (naphthols 1f-g) and ethyl acetoacetate 2, were used as the main precursors to obtain corresponding 4-methylcoumarins 3b-g in good yields under solvent-free conditions and at room temperature (Figure 4). It is important to note that no reported ball milling or grinding procedure [41][42][43][44] offered the direct preparation of 7amino-4-methylcoumarin. The identity of the products 3a-g (Table 1) was confirmed by their IR, 1 H NMR, 13 C NMR, and mass spectral data and by comparison with authentic samples.…”

“…In this context, Pechmann condensation still attracts a lot of attention from synthetic chemists. Indeed, recently, various interesting protocols for coumarin ring construction based on green chemistry principles have been reported [36][37][38][39][40][41][42][43][44]. These procedures do not only focus on the effectiveness of a catalyst or its reusability but also its safety for both mankind and the environment using several alternative physical methods.…”

“…Although the hand-grinding technique is an easy and inexpensive approach, mechanical milling using a mixer mill or planetary mill by grinding balls (ball-milling) is becoming a more promising green tool for the synthesis of organic molecules, including heterocyclic In this context, Pechmann condensation still attracts a lot of attention from synthetic chemists. Indeed, recently, various interesting protocols for coumarin ring construction based on green chemistry principles have been reported [36][37][38][39][40][41][42][43][44]. These procedures do not only focus on the effectiveness of a catalyst or its reusability but also its safety for both mankind and the environment using several alternative physical methods.…”

“…Using "porcelain mortar-pestle" as the manual grinding tool, Indian researchers described for the first time the synthesis of coumarins via Pechmann condensation under solvent-free conditions by applying a grinding technique. They reported higher yields of the obtained 4-methylcoumarin derivatives; however, two equivalents of catalysts (p-TsOH and P 2 O 5 ) to the starting phenols were used [41][42][43]. It is known that manual grinding, carried out by a person, is a labor-intensive and non-automatic process, which often raises some concerns, including the kinetic parameters of the reaction and the reproducibility [51].…”

Recent Advances in Synthesis of 4-Arylcoumarins

“…As an alternative approach, Pechmann condensation using solid supports has been devised ( Table 2 ). Silica-supported solid catalysts such as silica chloride [ 38 ], silica-supported sulfuric acid [ 39 , 40 ], silica gel-supported zirconyl chloride ocatahydrate [ 41 ], silica-supported boric trisulfuric anhydride [ 42 ], and SnCl 4 grafted on silica gel [ 43 ] have been applied successfully for the synthesis of 4-arylcoumarins via the Pechmann condensation (Entry 1–6). Silica supports have the advantages of good accessibility, excellent chemical and thermal stability, and large surface area for easy functionalization.…”