[Et3NH][HSO4]-catalyzed eco-friendly and expeditious synthesis of thiazolidine and oxazolidine derivatives

Abstract

The present study reports a facile and green approach for the synthesis of thiazolidine/oxazolidine derivatives 4(a–u) in excellent yields (92–98%) with high purity. The protocol involves a one-pot three-component reaction of substituted 1,3-diketones 1(a–g), cyanates 2(a–c) and ethylchloroacetate (3) in ionic liquid [Et₃NH][HSO₄] under solvent-free conditions. The notable feature of this pathway is that the ionic liquid possesses both catalytic as well as medium engineering capability in this protocol. Use of [Et₃NH][HSO₄] as a catalyst and an environmentally benign solvent eliminates the need for a volatile organic solvent and additional catalyst. This ionic liquid is air and water stable and easy to prepare from cheap amine and acid. The present synthetic route is a green protocol offering several advantages, such as excellent yield of products, mild reaction conditions, minimizing chemical waste, shorter reaction time, simple operational procedure, easy preparation of the catalyst and its recyclability up to five cycles without any noticeable loss in catalytic activity. The protocol is applicable to a broad substrate scope. The optimization of conditions carried out in the present study revealed that 20 mol% of ionic liquid catalyst under solvent-free conditions at 120 °C are the best reaction parameters for the synthesis of thiazolidine/oxazolidine derivatives in excellent yields.