NUCLEOPHILIC VINYLIC SUBSTITUTIONS OF (Z)-(BETA-HALOALKENYL)PHENYLIODONIUM SALTS WITH SODIUM BENZENESULFINATE - FIRST EVIDENCE OF A MICHAELADDITION OF NUCLEOPHILES TO ALKENYLIODONIUM SALTS AT THE C-BETA ATOM

Evidence for a Michael addition of a nucleophile to alkenyl(phenyl)iod onium salts at the C-beta atom is reported here for the first time. Nu cleophilic vinylic substitutions of (Z)-(beta-chloroalkenyl)- 2b and ( Z)-(beta-bromoalkenyl)iodonium tetrafluoroborates 3b with sodium benze nesulfinate in THF afforded stereoselectively (Z)-1,2-bis(benzenesulfo nyl)alkene 5b with retention of configuration. Intermediate formation of (Z)-(beta-(benzenesulfonyl)alkenyl)iodonium salt 9b in these reacti ons was established by H-1 NMR experiments in CDCl3. The formation of (Z)-9b involves a hitherto unobserved Michael addition of benzenesulfi nate anion to the alkenyliodonium salts at the C-beta atom, followed b y halogen extrusion. The formation of a stereoisomeric mixture of(Z)-a nd (E)-bis-sulfones 5b, and 1-(benzenesulfonyl)cyclopentene 11 that wa s observed in the reaction of (Z)-(beta-fluoroalkenyl)iodonium salt 4b in CDCl3, strongly suggests the intermediacy of 9b in this nucleophil ic vinylic substitution.