Allylation of acetals and ketals with allyltrimethylsilane catalyzed by the mixed Lewis acid system AlBr3/CuBr

The synthesis of homoallyl ethers from various acetals and a cyclic ketal with allyltrimethylsilane catalyzed by aluminum bromide in the presence of trimethylaluminum as a desiccant is described. We found that the addition of a catalytic amount of copper(I) bromide accelerates the allylation reactions to afford the homoallyl ether derivatives in good to excellent yield.