A metal-free cascade reaction of β-halo-α,β-unsaturated aldehydes and 1,4-dithiane-2,5-diols: synthesis of polycyclic 2-formylthiophenes.

Abstract

A metal-free cascade reaction strategy has been developed for the synthesis of novel polycyclic 2-formylthiophenes from β-halo-α,β-unsaturated aldehydes and 1,4-dithiane-2,5-diols. A recyclable polymer supported organic base was used to perform the reaction process. This synthetic protocol was applied to synthesize several novel polycyclic thiophenes including steroidal D-ring annelated thiophene. Our synthetic strategy provides a high yield of thiophenes, avoids a tedious work-up procedure and minimizes the formation of waste.