作者:Sreekanth A. Ramachandran、Rajendra K. Kharul、Sylvain Marque、Pierre Soucy、Frédéric Jacques、Robert Chênevert、Pierre Deslongchamps
DOI:10.1021/jo0608725
日期:2006.8.1
Stereoselectivesynthesis of the potentially biologically valuable 5β-lanosteroidal-type backbone was achieved via anionic cycloaddition. Synthesis of the two new bicyclic Nazarov intermediates 14 and 40 and their cycloaddition with chiral cyclohexenone 25 and further functional group manipulations resulted in highly functionalized tetracyclic intermediates 28 and 44. These synthetic intermediates
Herein we report a convergent enantioselective synthesis of a polyfunctionalized ABCD tetracycle by using an anionic cycloaddition reaction between a chiral bicyclic CD Nazarov intermediate (see 6), derived from the (−)-Weiland–Mischer ketone, and an achiral cyclohexenone (see 5) adequately functionalized to furnish the ring A of pentacyclictriterpenes (Scheme 5). The chiral bicyclic CD Nazarov intermediate