Photochemical Arylation Reactions by 4‐Chlorothioanisole

Abstract

AbstractThe photochemistry of 4‐chlorothioanisole (1) was investigated in various solvents, and it was found to involve the reduction to thioanisole as the main process. This occurs by heterolytic fragmentation of the triplet state of 1 and formation of the triplet 4‐thiomethoxyphenylium ion, as supported by DFT calculations. The cation is trapped by alkenes and, less efficiently, by benzene, resulting in new examples of the recently emerging arylation reactions by SN1 substitution of phenyl halides. The products from alkenes involve the phenonium ion as a further intermediate. The product distribution differs from the analogous reactions via 4‐methoxyphenylium for including a larger proportion of 4‐(β‐substituted alkyl)‐ rather than 4‐allylthioanisoles derivatives in alcohols, for the lower fraction of rearranged α‐substituted 4‐alkylthioanisoles and for the formation of some 4‐cyclopropylthioanisole with allyltrimethylsilane. The difference is accounted for by the more developed dipolar character of the C–C cyclopropane bonds in the intermediate phenonium, as indicated by DFT calculations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)