Mechanistic Study of Diarylamines: Photoinduced [6Pi]-Electrocyclization, Solvent Effects, Photophysical Properties, and Preparative Photochemistry

The Carbazole Scaffold consists of a heterocyclic system of great interest in science and technology.^1,2 A synthetic sequence for the preparation of substituted Carbazoles is presented, involving two consecutive reactions. The first one is the C–N coupling reaction developed by Stephen L. Buchwald and John F. Hartwig. The second reaction involves a photoinduced electrocyclization step that allows the formation of carbazoles, involving the triplet electronic state, generation of the 4a,4b-dihydrocarbazole intermediate, which, in the presence of molecular oxygen, rearomatizes to afford the desired carbazole with concomitant release of hydrogen peroxide.

In this work, the synthesis of several meta- and para-substituted diarylamines is presented as synthons for the preparation of endo/exo carbazoles. Additionally, a mechanistic study of the photoreaction will be carried out, focusing on: (i) the substituent effect, (ii) the endo/exo regiochemistry, (iii) the solvent effect, (iv) the measure of quantum yields, and (v) identification of the photoreactive state.