Asymmetric Diels−Alder Reactions Catalyzed by a Triflic Acid Activated Chiral Oxazaborolidine
作者:E. J. Corey、Takanori Shibata、Thomas W. Lee
DOI:10.1021/ja025848x
日期:2002.4.1
generation of chiral Lewis superacids by protonation of a non-Lewis acidic oxazaborolidine (1) with triflic acid. The resulting cationic species (3) are powerful and highly enantioselective catalysts for the Diels-Alder reaction of various 1,3-dienes with alpha,beta-enals. An optimization study (see Table 1) led to the selection of reaction conditions and catalysts (6A and 6B) which are very effective. The
BBr3-chiral phosphoric acid complexes are highly effective and practical Lewis acid-assisted Brønsted acid (LBA) catalysts for promoting the enantioselective Diels-Alder (DA) reaction of α-substituted acroleins and α-CF3 acrylate. In particular, the DA reaction of α-substituted acroleins with 1,2-dihydropyridines gave the corresponding optically active isoquinuclidines with high enantioselectivities