Photoinduced, ionic Meerwein arylation of olefins

Irradiation of 4-chloroaniline or of its NN-dimethyl derivative in polar so lvents generates the corresponding triplet phenyl cations. These are trappe d by alkenes yielding arylated products in medium to good yields. B3LYP cal culations show that the triplet cation slides with negligible activation en ergy to a bonded adduct with ethylene, whereas it forms only a marginally s tabilized CT complex with water (chosen as a representative sigma nucleophi le). The structure of the final products depends on the preferred path from the adduct cation with the alkene. In the case of aryl olefins, this depro tonates to stilbene derivatives, while, from 2,3-dimethyl-2-butene and ally trimethylsilane, allylanilines are obtained by elimination of an electrofug al group in gamma. In the case of mono- and disubstituted alkenes the catio n adds chloride rather than eliminating and beta -chloroalkylanilines are o btained. The regio- and sterochemistry of the addition across the alkene ar e best understood with a phenonium ion structure for the adduct. The nucleo phile entering in beta can be varied under conditions in which the adduct c ation is trapped more efficiently than the starting phenyl cation. Thus, be ta -methoxyalkylanilines are formed when the irradiation is carried out in methanol. beta -Iodoalkylanilines are obtained in acetonitrile containing i odide and unsubstituted alkylanilines in the presence of sodium borohydride . A case of intramolecular nucleophilic trapping is found with 4-pentenoic acid. The reaction is a wide-scope ionic analogue of the radicalic Meerwin arylation of olefins.