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 C_β Atom

Abstract

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.

Metal‐Free [2+2+1] Annulation of Alkynes, Nitriles and Nitrogen Atoms from Iminoiodanes for Synthesis of Highly Substituted Imidazoles

“…That is, intermediates trans-B and/or cis-B would be formed through the activation of alkyne 1 by iodonium species A (and/or A') and then the Ritter-type addition of R 3 CN. [22] Since alkenyliodanes bearing a leaving group at the b-position have been known to undergo a nucleophilic vinylic substitution, [23] considering the presence of the large excess amount of nitrile and leaving ability of a unilateral nitrile of bis-nitrilium intermediate, trans-B may be converted to cis-B by the addition and elimination of R 3 CN. Subsequently, the cyclization of cis-B followed by the reductive elimination of PhI in intermediate C give the target imidazoles 2 and 4-6.…”

α‐Arylation by Rearrangement: On the Reaction of Enolates with Diaryliodonium Salts

“…[15] SET mechanisms can operate, [16] but in the case of enolate arylation, product distribution studies and results using radical inhibitors argue against the involvement of radicals or benzynes. [17][18][19] Based on the mechanism described above, we hypothesized that asymmetric induction could be achieved in several ways. Two approaches were investigated, one involving a diaryliodonium salt with a chiral anion (X* À ) and the other using chiral phase-transfer catalysis (PTC* + ).…”

“…[18] As discussed above, the reaction could follow associative or dissociative ligandexchange pathways, that is, the enolate could react with neutral A or cationic B (Scheme 3). Either pathway could give intermediate C or D, with oxygen or carbon bonded to iodine.…”

α-Functionalization of Carbonyl Compounds Using Hypervalent Iodine Reagents

“…iodonium tetrafluoroborates (Scheme 68). [133] Competing α-arylation could be avoided by using a pmethoxyphenyl moiety. In this detailed study, the use of an aryl radical trap inhibited radical-induced decomposition of the alkenyl(aryl)iodonium salts, thereby improving the yields.…”