Triethylborane-induced radical reactions with gallium- and indium hydrides

A gallium hydride reagent, HGaCl2, was found to act as a radical mediator. Treatment of alkyl halides with the gallium hydride reagent, generated from gallium trichloride and sodium bis(2-methoxyethoxy)aluminum hydride, provided the corresponding reduced products in excellent yields. Radical cyclization of halo acetals was also successful with not only the stoichiometric gallium reagent but also a catalytic amount of gallium trichloride combined with stoichiometric aluminum hydride as a hydride source. An indium hydride reagent, HInCl2, prepared from indium trichloride and diisobutylaluminum hydride also worked as a radical mediator. HInCl2 could reduce aryl iodides and bromides in the presence of Et3B as a radical initiator.