Mechanistic insights into perfluoroaryl borane-catalyzed allylstannations: Toward asymmetric induction with chiral boranes

Morrison, D. J.; Blackwell, J. M.; Piers, W. E.

doi:10.1351/pac200476030615

Pure Appl. Chem., 2004, Vol. 76, No. 3, pp. 615-623

http://dx.doi.org/10.1351/pac200476030615

Mechanistic insights into perfluoroaryl borane-catalyzed allylstannations: Toward asymmetric induction with chiral boranes

D. J. Morrison, J. M. Blackwell and W. E. Piers

Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta T2N 1N4, Canada

Abstract: The perfluoroaryl borane B(C₆F₅)₃ is an effective catalyst for a variety of organic transformations. In the hydrosilation of carbonyl functions, it activates the silane rather than the carbonyl substrate. In allylstannation reactions, two competing reaction pathways are observed, one involving tin cation catalysis, the other "true" borane catalysis. For B(C₆F₅)₃, the former mechanism dominates, while for the weaker Lewis acid PhB(C₆F₅)₂, the latter pathway is more prominent. Thus, chiral boranes of similar Lewis acid strength to PhB(C₆F₅)₂ have the potential to mediate asymmetric allylstannation of aldehyde substrates.