Using 1-butyl-3-methylimidazolium bromide [bmim]Br as an efficient catalyst for one-pot green synthesis of 4H-benzo[b]pyrans and 3,4-dihydropyrimidin-2-(1H) ones

ILs are ionic compounds in which, at last the cation is an organic type cation. ILs contains only ionic species and sometime are known as molten salt, however while a molten salt is generally thought to refer to a high-melting, highly viscous and very corrosive medium, ionic liquids are already liquid at low temperatures ( 100℃) and have relatively low viscosity. The apparently somewhat arbitrary line drawn between molten salts and ILs at a melt temperature of 100℃ can be justified by the abrupt improvement in the range of applications for liquid salts below this temperature. Even though some examples are known in which high-temperature salt melts have been successfully used as reaction media for synthetic applications, only a liquid range below 100℃ can enable the versatile substitution of conventional, organic solvents by ionic liquid [1]. Among the heterocycles, functionally substituted 4H-chromenes have received considerable attention due to their spasmolytic, diuretic, anti-coagulant, anti-cancer and anti-anaphylactic activities [2]. 4H-benzo[b]pyrans are an important class of compounds which have received considerable attention in recent years due to their wide range of biological activities [3]. Dihydropyrimidinones (DHPMs) as well as heterocyclic compound in the natural and synthetic organic chemistry due to their wide range of biological and therapeutic properties such as anti-viral anti-inflammatory, anti-tumor, and anti-bacterial activities[4]. A simple, efficient, and high yielding procedure for the preparation of 4H-benzo[b]pyrans and 3,4-dihydropyrimidin-2(1H)-ones is described using ionic liquid 1-butyl-3-methylimidazolium bromide [bmim]Br as a heterogeneous and efficient catalyst under ultrasonic and solvent-free conditions. Simple methodologies, easy work-up procedure, easy preparation of the catalyst, excellent yields, and very short reaction times are among the other advantages of this study. Furthermore, this ionic liquid can be easily recovered.