Zinc- and Indium-Mediated Ring-Expansion Reaction of α-Halomethyl Cyclic β-Keto Esters in Aqueous Alcohol

Radical ring-expansion reaction of various α-halomethyl cyclic β-keto esters and α-halomethyl benzocyclic β-keto esters and chain-extension reaction of α-halomethyl β-keto esters with zinc powder and indium powder in refluxing aqueous alcohol were carried out to generate the corresponding ring-expansion and chain-extension products. As the results indicate, it was found zinc powder was more effective than indium powder to give the corresponding ring-expanded products in quite good yields. Moreover, the addition of zinc bromide as Lewis acid showed an increase of the yields, depending on the substrates. The present reaction conditions are highly effective, simple, and environmentally friendly.