Chiral Oxazaborolidine−Aluminum Bromide Complexes Are Unusually Powerful and Effective Catalysts for Enantioselective Diels−Alder Reactions
Journal of the American Chemical Society2007Vol. 129(6), pp. 1498–1499
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Abstract
Treatment of the chiral oxazaborolidine 1 with AlBr3 generates the 1:1 complex 3, which is an even more potent Lewis acid catalyst than protonated 1 (i.e., 2) for enantioselective Diels−Alder reactions. Only 4 mol % of catalyst 3 is required to achieve yields and enantiomeric purities of 90% over a broad range of achiral dienes and dienophiles. The ligand from which 3 is derived can be recovered easily and with high efficiency. The method is illustrated by 22 examples.