Nucleophilic Vinylic Substitutions of (Z)-(β-Haloalkenyl)phenyliodonium Salts with Sodium Benzenesulfinate:  First Evidence of a Michael Addition of Nucleophiles to Alkenyliodonium Salts at the Cβ 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 (1)H NMR experiments in CDCl(3). 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 CDCl(3), strongly suggests the intermediacy of 9b in this nucleophilic vinylic substitution.