Triethylborane-induced radical allylation of α-halo carbonyl compounds with allylgallium reagent in aqueous media

An allylgallium reagent is found to be effective for radical allylation of α-iodo or α-bromo carbonyl compounds. Treatment of benzyl bromoacetate with allylgallium, prepared from allylmagnesium chloride and gallium trichloride, in the presence of triethylborane in THF provided benzyl 4-pentenoate in good yield. The addition of water as a cosolvent improved the yields of allylated products. It was revealed that the allylgallium species resists immediate decomposition on exposure to water.