Further studies into the trapping of photo-NOCAS reaction intermediates : amines as the nucleophiles

Abstract

Previous studies managed to trap a P-alkoxy radical, a key intermediate in a well established Photo-NOCAS reaction, (nucleophilic olefin combination aromatic substitution) by using electron poor alkenes, such as acrylonitrile or methylacrylate. The P-alkoxy radical is formed by a nucleophilic attack of an alcohol on an alkene radical cation, generated by a photochemical reaction between electron rich alkenes and dicyanobenzenes. Then the P-alkoxy radical is intercepted by the trapping reagent, before it couples with the radical anion of dicyanobenzene, preventing the formation of the photo-NOCAS product, a 1: 1: 1 adduct. The trapping stage is equivalent to the combination of an electron poor alkene with an electron rich olefin. Recent studies have reported the formation of similar photo-NOCAS products, in the presence of electron rich alkenes, like 2,3-dimethybut-2-ene and trans-anethole, dicyanobenzenes and amines as nucleophiles. The mechanism proposed for these photochemical reactions is similar to that described for alcohols. Therefore, in this preliminary study, the formation of these photo-NOCAS products was further studied in order to adopt the trapping reaction for these systems. The idea involved the trapping of the P-alkylamino radical for these reactions, analogous to P-alkoxy radicals, by acrylonitrile. While investigations involving 2,3-dimethylbut-2-ene and trans-anethole were not fruitful, as for the attempted trapping of a P-amino radical, in the case of trans-anethole an unexpected product appears to have been formed. This product resulted from a secondary photochemical step following the formation of a primary product, itself resulting from the photoinduced (electron transfer) addition of methylamine to trans anethole. In this second step, acrylonitrile is incorporated into the primary product. Mechanistic details are proposed.