Solvolysis of Vinyl Iodonium Salts. New Insights into Vinyl Cation Intermediates

Abstract

Solvolysis of some vinyl iodonium salts carrying an excellent leaving group is examined, focusing on whether or not a classical primary vinyl cation can be generated. Formation of the primary cation is avoided, when possible, by participation of the beta substituent in the heterolysis to form a vinylenebenzenium ion or a secondary vinyl cation. Definitive evidence against a primary vinyl cation is provided by a chirality probe approach in the solvolysis of 4-methylcyclohexylidenemethyl iodonium salt.

Photo‐Cross‐Coupling Reaction of Electron‐Rich Aryl Chlorides and Aryl Esters with Alkynes: A Metal‐Free Alkynylation

“…18 We surmised that phenyl cations would react with triple bonds to yield β‐phenylvinyl cations, or more probably cyclic vinylenebenzenium ions (Scheme ). The last species have been invoked as intermediates in the thermal solvolysis of styryliodonium tetrafluoroborate19 and in the photoheterolysis of ( E )‐bromostyrene20 (Scheme ).…”

Chemistry of Polyvalent Iodine

“…Various mechanisms, including S N 1, S N 2, ligand coupling, and Michael addition-elimination have been observed in these reactions. The mechanistic aspects of the reactions of vinylic iodonium salts with nucleophiles have been reviewed by Okuyama47,791 and by Ochiai 36,38…”

“…Numerous reviews on specific classes of polyvalent iodine compounds and their synthetic applications have recently been published 18–61. Most notable are the specialized reviews on [hydroxy(tosyloxy)iodo]benzene,41 the chemistry and synthetic applications of iodonium salts,29,36,38,42,43,46,47,54,55 the chemistry of iodonium ylides,56–58 the chemistry of iminoiodanes,28 hypervalent iodine fluorides,27 electrophilic perfluoroalkylations,44 perfluoroorgano hypervalent iodine compounds,61 the chemistry of benziodoxoles,24,45 polymer-supported hypervalent iodine reagents,30 hypervalent iodine-mediated ring contraction reactions,21 application of hypervalent iodine in the synthesis of heterocycles,25,40 application of hypervalent iodine in the oxidation of phenolic compounds,32,34,50–53,60 oxidation of carbonyl compounds with organohypervalent iodine reagents,37 application of hypervalent iodine in (hetero)biaryl coupling reactions,31 phosphorolytic reactivity of o -iodosylcarboxylates,33 coordination of hypervalent iodine,19 transition metal catalyzed reactions of hypervalent iodine compounds,18 radical reactions of hypervalent iodine,35,39 stereoselective reactions of hypervalent iodine electrophiles,48 catalytic applications of organoiodine compounds,20,49 and synthetic applications of pentavalent iodine reagents 22,23,26,59…”

Polyvalent iodine in organic chemistry: Recent developments, 2002–2005

“…The phenyliodonio group is evaluated to be 10 6 times as effective a nucleophuge as the triflate leaving group or 10 12 times more reactive than the iodo group itself. This value shows that the iodonio group is the most efficient leaving group ever determined quantitatively [77]. A plausible mechanism of these reactions included the formation of ST complex (single-transfer complex) yielding aromatic cation radicals, which react with nucleophile by oneelectron oxidation followed by deprotonation to give the product-for example, see Scheme 39 [78,79].…”