A New Chiral BLA Promoter for Asymmetric Aza Diels-Alder and Aldol-Type Reactions of Imines
摘要:
A new type of chiral promoter for double asymmetric inductions of aza Diels-Alder and aldol-type reactions of imines is prepared from trialkyl berates (B(OMe)(3) or B(OPh)(3)) and optically pure binaphthol; X-ray analysis of the boron complex demonstrates that it exists as a Bronsted 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 beta-amino acid esters with high enantioselectivity. The solution conformations of the BLA.imine complexes have been studied using H-1 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 Bronsted acid.
Asymmetric aza-Diels-Alder reaction: enantio- and diastereoselective reaction of imine mediated by Chiral Lewis acid
作者:Kouji Hattori、Hisashi Yamamoto
DOI:10.1016/s0040-4020(01)80532-9
日期:1993.2
asymmetric aza-Diels-Alder reaction usingchiral boron mediator is developed. The key to its success is the use of the chiral boron complex prepared in situ from (R)- or (S)- binaphthol and B(OPh)3. The enantiomeric reaction of prochiral imine affords products of up to 90% ee. The double asymmetric induction of chiral imine using α-benzylamine as a chiralauxiliary is achieved with almost complete diastereoselectivity
作者:Cody Timmons、Adiseshu Kattuboina、Lauren McPherson、James Mills、Guigen Li
DOI:10.1016/j.tet.2005.10.018
日期:2005.12
The aza Diels-Alder reaction is described for a novel diene. Imines bearing benzyl and aromatic protecting groups both work well. Moderate diastereoselectivities can be obtained using the simple alpha-methylbenzyl chiral auxiliary. (c) 2005 Elsevier Ltd. All rights reserved.