Journal of the American Chemical Society p. 10520 - 10524 (1994)
Update date:2022-07-29
Topics:
Ishihara, Kazuaki
Miyata, Mayumi
Hattoi, Kouji
Tada, Toshiji
Yamamoto, Hisashi
A new type of chiral promoter for double asymmetric inductions of aza Diels - Alder and aldol-type reactions of imines is prepared from trialkyl borates (B(OMe)3 or B(OPh)3) and optically pure binaphthol; X-ray analysis of the boron complex demonstrates that it exists as a Br?nsted acid-assisted chiral Lewis acid (BLA). The aldol-type reactions of a number of N-benzhydrylimines derived from aromatic aldehydes with the ketene silyl acetal derived from tert-butyl acetate mediated by the chiral BLA afford β-amino acid esters with high enantioselectivity. The solution conformations of the BLA·imine complexes have been studied using 1H NMR analysis and difference NOE measurements. The absolute configurations of the adducts can be understood in terms of a rational model involving an intramolecular hydrogen binding interaction via a Br?nsted acid.
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