Aldehyde addition to allylic stannanes via a transmetallation pathway: Stereocontrol in the absence of internal coordination

Methyltin trichloride and indium(III) chloride promote the addition of aldehydes to cyclic allylic stannanes providing good yields of the corresponding homoallylic alcohols. These reactions proceed via an initial transmetallation involving anti approach of the electrophile, followed by syn aldehyde addition that is erythro selective. These Lewis acids do not promote the corresponding addition of imines, rather providing the same homoallylic alcohols after an in situ aqueous hydrolysis. Imine addition is possible with boron trifluoride-diethyl ether as the Lewis acid.