Catalyst-free, step and pot economic, efficient mercaptoacetylative cyclisation in H2O: synthesis of 3-mercaptocoumarins

A novel, environmentally friendly, tandem Knoevenagel condensation and mercaptoacetylative cyclisation procedure is reported. The reaction between 2-methyl-2-phenyl-1,3-oxathiolan-5-one and a variety of salicylaldehydes was carried out in water to afford 3-mercaptocoumarins in excellent yields (82-97%). In this green synthetic protocol, water itself catalyses the reaction by hydrogen bonding and thus avoids the use of any other catalyst. Acetophenone obtained as a by-product was also recovered and recycled easily for further use.