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Bifuctional Amino-Squaramides Catalyzed Asymmetric Spiroannulation Cascades with Aliphatic β,γ-Unsaturated α-Keto Esters: Controlling an Aldehyde Enolate

Author:
Wang, Xiaoqin, Yao, Weijun, Yao, Zhihui, Ma, Cheng
Source:
Journal of organic chemistry 2012 v.77 no.6 pp. 2959-2965
ISSN:
1520-6904
Subject:
aldehydes, catalysts, cyclization reactions, esters, moieties, nitrogen, organic chemistry, stereochemistry
Abstract:
A quinidine-derived squaramide Ib catalyzed cyclization reaction of β-oxo aldehydes 1 and aliphatic or aromatic β,γ-unsaturated α-keto ester 2 is described. Using cyclic aldehyde substrates, this procedure provided a promising approach to a variety of spiro-3,4-dihydropyrans bearing three continuous quaternary and tertiary stereocenters in moderate to good yield with high stereoselectivities. Substituents on the nitrogen atoms of the squaramide moiety of the catalyst proved crucial to the reaction outcome. The stereochemistry of the three newly formed chiral centers (trans-selective) of the major product indicates a Micheal addition/hemiacetalization domino sequence for the present annulations.
Agid:
5499709