The Origin of the Regioselectivity in the 2+2 Photochemical Cycloaddition Reactions of N-Benzoylindole with Alkenes: Trapping of 1,4-Biradical Intermediates with Hydrogen Selenide

Article abstract of DOI:10.1016/S0040-4039(00)79875-3

The 1,4-biradical species previously proposed as intermediates in the formation of cyclobutane adducts in the photochemical cycloaddition reaction between N-benzoylindole and alkenes have been trapped with hydrogen selenide.The structures of the trapped biradicals are consistent with the proposal that the first bond formed between the triplet excited state of the indole derivative and the alkenes is from the indole 2-position to that terminus of the alkene which is less able to stabilise a radical centre.This allows prediction of the reaction regiochemistry.Key Words: N-benzoylindole; photochemical cycloaddition; 1,4-biradicals; trapping.