Intramolecular Cyclization of Acyloxy Sulfones to Fused Furans and Benzofurans

Significance

Reported is the synthesis of fused furan and benzofuran ring systems through an ­intramolecular cyclization of unsaturated acyloxy sulfone derivatives. Thus, exposure of allylic or benzylic sulfones to LHMDS leads to acyl group transfer to form intermediates, which upon an acid-promoted cyclization-dehydration sequence afford stable heteroaromatic ring systems. A narrow investigation of the substrate scope revealed that, although both allylic and phenolic esters perform well in this process, the latter required elevated temperature to progress to completion. In addition, the synthesis of two fused pyrans was demonstrated using the same procedure.