Nucleophilic vinylic substitutions of (Z)-(beta-haloalkenyl)phenyliodonium salts with sodium benzenesulfinate: First evidence of a Michael addition of nucleophiles to alkenyliodonium salts at the C-beta atom

Evidence for a Michael addition of a nucleophile to alkenyl(phenyl)iodonium salts at the C-beta atom is reported here for the first time. Nucleophilic vinylic substitutions of (Z)-(beta-chloroalkenyl)- 2b and (Z)-(beta-bromoalkenyl)iodonium tetrafluoroborates 3b with sodium benzenesulfinate in THF afforded stereoselectively (Z)-1,2-bis(benzenesulfonyl)alkene 5b with retention of configuration. Intermediate formation of (Z)-(beta-(benzenesulfonyl)alkenyl)iodonium salt 9b in these reactions was established by H-1 NMR experiments in CDCl3. The formation of (Z)-9b involves a hitherto unobserved Michael addition of benzenesulfinate anion to the alkenyliodonium salts at the C-beta atom, followed by halogen extrusion. The formation of a stereoisomeric mixture of(Z)-and (E)-bis-sulfones 5b, and 1-(benzenesulfonyl)cyclopentene 11 that was observed in the reaction of (Z)-(beta-fluoroalkenyl)iodonium salt 4b in CDCl3, strongly suggests the intermediacy of 9b in this nucleophilic vinylic substitution.