Facile synthesis of 5-arylidene rhodanine derivatives using Na2SO3 as an eco-friendly catalyst. Access to 2-mercapto-3-aryl-acrylic acids and a benzoxaborole derivative

A simple, efficient and environment-friendly procedure for the synthesis of 5-arylidene rhodanines derivatives via a Knoevenagel type reaction was developed using rhodanine, variety differently substituted aldehydes Na2SO3 as benign catalyst in ethanol. Selected were subjected to basic hydrolysis afford 2-mercapto-3-substituted-acrylic acids. The presence boronic acid group is well tolerated such transformations. In case 2-formylphenylboronic acid, this sequence opens access new benzoxaborole derivative.