Mechanistic Studies on Selectivity in the B(C6F5)3-Catalyzed Allylstannation of Aldehydes: Is Hypercoordination at Boron Responsible?

[structure: see text] The selective, B(C6F5)3-catalyzed allylstannation of aldehydes with proximal donor groups is shown to proceed via borane abstraction of the allyl group from the tin reagent and activation of the substrate by "Bu3Sn+". This is supported by a number of 19F NMR experiments. The selectivity of the reaction is not attributable to hypercoordinate boron as proposed by the discoverers of this highly selective reaction but likely involves chelation at tin.