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[摘要]：The asymmetric aldol reaction of heteroatom-substituted ketene silyl acetals with achiral aldehydes has been developed by the promotion of tin(II) triflate coordinated with a chiral diamine to afford the corresponding aldols having chiral tertiary alcohols at the a-positions. This reaction has been successfully applied to the construction of the basic skeletons of buergerinins F and G starting from achiral materials. (+)-Buergerinin G, a potentially antiphlogistic and febrifuge agent having a unique trioxatricyclo[5.3.1.0(1,5)]undecane skeleton, is stereoselectively prepared by means of the enantioselective aldol reactions via ten linear steps from crotonaldehyde in 18% overall yield including an effective intramolecular Wacker-type ketalization of the dihydroxy-gamma-lactotie as a key step. In addition to the former establishment for the synthesis of (+)-buergerinin F, effective divergent methods for the preparation of buergerinins F and G were developed through a unified optically active aldol-type intermediate, which was generated from the tetrasubstituted ketene silyl acetal with crotonaldehyde by the asymmetric Mukaiyama aldol reaction. |
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