A novel base-induced cyclization of selected benzyl alkynyl sulfides for the synthesis of 2-aryl-2,3-dihydrothiophenes

2-Halobenzyl 1-alkynyl sulfides undergo an unprecedented dihydrothiophene formation when treated with 2 equiv. of KOtBu in CH3CN. The reaction, believed to proceed via a 5-endo-dig cyclization, is sluggish or non-existent in the absence of the halogen.