Nucleophilic vinylic substitution and vinyl cation intermediates in the reactions of vinyl iodonium salts

Vinyl(aryl)iodonium salts are good electrophiles carrying an excellent nucleofuge, an iodoarene, which makes them good substrates for nucleophilic substitution (SN2) as well as versatile precursors for vinyl cations (SN1). For the vinylic SN2 reactions, two pathways are possible: SNVσ and SNVπ leading to inversion and retention of configuration, respectively. Primary vinyl cations are unstable both thermodynamically and kinetically, and their thermal generation from vinyl iodonium salts is avoided by participation of the trans β-phenyl or β-alkyl groups or an external nucleophile. In contrast, photoexcited vinyl iodonium ions readily undergo heterolysis to give primary cations. © 2002 Elsevier Science B.V. All rights reserved.