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.
*Plenary and invited lectures presented at the 12th
International Symposium on Organometallic Chemistry Directed Towards
Organic Synthesis (OMCOS-12), Toronto, Ontario, Canada, 6-10 July 2003.
Other lectures are published in this issue, pp.
453-695.
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