REACTION OF DIPHENYL DISULFIDE WITH ALKYNES PROMOTED BY DI-TERT-BUTYL AND DIBENZOYL PEROXIDE - A USEFUL SYNTHETIC ROUTE TO 3-SUBSTITUTED (AND 2,3-) SUBSTITUTED BENZO[B]THIOPHENES

Thermal reactions of diphenyl disulfidel with phenylacetylenes 2a-e promoted by di-tert-butyl peroxide (TBP) at 110 or 150-degrees-C provides a useful synthetic route to the (2-substituted) 3-phenylbenzo-[b]thiophenes 4a-e, which result from intramolecular cyclization of 1-phenyl-2-(phenylthio)vinyl radical intermediates 3a-e. Similar reactions of the disulfide 1 with tert-butyl-and trimethylsilyl-acetylenes 2f and 2g also provide the corresponding benzothiophenes 4f and 4g in satisfactory yields; low yields of the benzothiophene products 4h, i, however, are obtained with hex- 1 -yne 1 h and hex-3-yne 1 i. Evidence is presented that the thermal reaction of the disulfide 1 with the alkynes 2 at 100-degrees-C in the presence of dibenzoyl peroxide, while being of little use for the synthesis of benzothiophenes 4, generally leads to the 2-(phenylthio)vinyl benzoates 10; this is ascribed to initial addition of benzoyloxy radicals to alkyne triple bonds.