Facile regioselective synthesis of 2H-thiopyrano[3,2-c]quinolin-5(6H)-ones by thio-Claisen rearrangement

A number of 1-alkyl-4-prop-2-ynylthioquinolin-2(1H)-one derivatives are synthesised by the phase transfer catalyzed reaction of 1-alkyl-4-marcaptoquinolin-2(1H)-ones with different prop-2-ynylic halides. These are then regioselectively cyclised in refluxing chlorobenzene to give hitherto unreported 2H-thiopyrano[3,2-c]quinolin-5(6H)-ones in 85–90% isolable yields.