A thioannulation approach to substituted thiophenes from Morita-Baylis-Hillman acetates of acetylenic aldehydes.

A new protocol has been developed for the synthesis of substituted thiophenes under mild and metal-free reaction conditions via the base-promoted thioannulation of Morita-Baylis-Hillman acetates of acetylenic aldehydes with potassium thioacetate involving a tandem allylic substitution/deacetylative 5-exo-dig-thiocycloisomerization. The obtained products provide an entry to 4H-thieno[3,2-c]chromene and thieno[3,2-c]dihydroquinoline.