GENERATION OF [BETA-(PHENYLSULFONYL)ALKYLIDENE]CARBENES FROM HYPERVALENT ALKENYLIODONIUM AND ALKYNYLIODONIUM TETRAFLUOROBORATES AND SYNTHESIS OF 1-(PHENYLSULFONYL)CYCLOPENTENES

Michael-type addition of benzenesulfinic acid to alkynyl(phenyl)iodonium tetrafluoroborates in methanol gives stereoselectively (Z)-(beta-(phenylsulfonyl)alkenyl)iodonium tetrafluoroborates in high yields. [beta-(Phenylsulfonyl)alkylidene]carbenes derived from the (Z)-(beta-(phenylsulfonyl)alkenyl)iodonium tetrafluoroborates by base treatment predominantly undergo intramolecular 1,5-carbon-hydrogen insertions to give 1-(phenylsulfonyl)cyclopentenes along with a small amount of rearranged alkynes, which is in a marked contrast with the facile 1,2-migration of beta-(phenylsulfenyl) and beta-(phenylsulfinyl) groups of alkylidenecarbenes. Reaction of alkynyl(phenyl)iodonium tetrafluoroborates with benzenesulfinates directly affords 1-(phenylsulfonyl)cyclopentenes via tandem Michael-carbene insertion reactions. The mechanism of 1,2-migration of [beta-(phenylsulfonyl)alkylidene]carbenes is also discussed.