Photochemische Addition von Anilinen an 1,3-Diene

Abstract

Anilines, e. g. aniline (12), N-methylaniline (16), 2,6-dimethyl-aniline (14), 2-(2'-butenyl)-N-methylaniline (4) or 2-(2'-cyclo-hexenyl)-N-methylaniline (8) when irradiated with a high pressure mercury lamp in methanol, acetonitrile, benzene or cyclohexane solution in the presence of an excess (3-60 fold) of 1,3-dienes, e.g. butadiene, trans-piperylene, isoprene or 1,3-cyclohexadiene yield corresponding N-allylated anilines (see Scheme 2-4). From butadiene and N-methylaniline (16) a 1:1 mixture of N-(1'-methylallyl)- and (E)/(Z)-N-(2'-butenyl)-N-methylaniline (18 and (E)/(Z)-19, respectively) is obtained, whereas trans-piperylene and 16 leads to the formation of (E)/(Z)-N-(1'-methyl-2'-butenyl)-N-methylaniline ((E)/(Z)-17, Scheme 3). Irradiation of 16 in the presence of isoprene causes the formation of four compounds, namely N-(1',1'-dimethyl-allyl)-, N-(3'-methyl-2'-butenyl)-, N-(1',2'-dimethylallyl)-, and (E)/(Z)-N-(2'-methyl-2'-butenyl)-N-methylaniline (21-24, Scheme 4), respectively. The structure of all compounds are in accord with the assumption that product formation occurs via an electron-donor-acceptor (EDA) complex of the aniline and the diene in the singlet state which collapses to radical pairs (anilinyl and allyl radicals) by intramolecular proton transfer from the N,H group to the 1,3-dienyl radical anion. The combination of the radical pair yields the observed N-allylated anilines (cf. Scheme 5).