Brønsted acid catalyzed annulations of ketene dithioacetals: synthesis of 3-aryl coumarins and indenes.

PTSA-catalyzed divergent synthetic routes toward 3-aryl coumarins and indenes have been developed using ketene dithioacetals. These transformations are transition-metal and oxidant free, proceed under mild conditions, and provide expeditious access to these important structural motifs.