Asymmetric Diels-Alder Reactions with Chiral 2-Methyl-1-(1-arylethoxy)-1,3-butadienes

Article abstract of DOI:10.1055/s-1990-26986

Chiral 1-arylethanols 2, prepared by enantioselective reduction of phenones 1 with lithium aluminium hydride and Chirald <(2S,3R)-(+)-4-dimethylamino-1,2-diphenyl-3-methylbutanol>, are converted to the chiral 2-methyl-1-(1-arylethoxy)-1,3-butadienes 5 by vinylogous transesterification with 2-methyl-1-ethoxyacrolein (3) and subsequent Wittig methylenation of the intermediate chiral 3-(1-arylethoxy)-2-methylacroleins 4.The 1-arylethyl isoprenyl ethers 5 undergo <4 + 2> cycloadditions as donor-activated 1,3-dienes with numerous electron-deficient dienophiles in good chemical yields and high diastereomeric excesses (>/= 95percent).The chiral inductor is removed optically pure from the cycloadducts by hydrogen chloride and silica gel in dichloromethane suspension at room temperature.