Organocatalytic Asymmetric Tandem Michael Addition−Hemiacetalization: A Route to Chiral Dihydrocoumarins, Chromanes, and 4<i>H</i>-Chromenes
作者:Dengfu Lu、Yajun Li、Yuefa Gong
DOI:10.1021/jo101446d
日期:2010.10.15
Asymmetric tandem Michael addition−hemiacetalization between aliphatic aldehydes and (E)-2-(2-nitrovinyl)phenols was investigated for constructing benzopyran backbones. Interestingly, the diastereo- and enantioselectivities changed markedly when the reaction was mediated by different types of secondary amine catalysts. The diphenylprolinol silyl ether 7 promoted the reaction with excellent enantioselectivities
of diphenyl prolinol trimethylsilylether, cis-3,4-disubstituted chromanols are obtained in high to excellent yields (81–98%) and stereoselectivities (dr: 86:14 to >99:1, ee 96 to >99%). The corresponding disubstituted chromans are available by dehydroxylation of the domino products in good to excellent yields (58–95%). Furthermore, oxidation of the domino products with pyridinium chlorochromate provided