Radical Allylations by Reaction of Azides with Allylindium Dichloride

Allylindium dichloride is an effective reagent for carrying out photolytically initiated radical allylation reactions, as also proved by EPR experiments. In the presence of suitable azides that can give rise to electrophilic radicals, a homolytic chain reaction occurs with formation of allylated compounds. With -azido esters and chlorides generation of primary indiumaminyl radicals is followed by a very efficient 1,5-H shift process that gives rise to electrophilic carbon-centred radicals, whose subsequent allylation by the starting indium reagent, followed by aqueous workup, eventually affords allylated nitrogen heterocycles in good yields. Some comparative theoretical calculations accounted for the observation that analogous reactions with an organoallyltin reagent did not work at all. The results show that the reaction with allylindium dichloride seems strongly favoured by both a lower BDE of the allyl-metal bond and a considerably faster, exothermic 1,5-H migration step.