Total syntheses of (+/-)-fawcettimine, (+/-)-fawcettidine, (+/-)-lycoflexine, and (+/-)-lycoposerramine B.

摘要

The total syntheses of (+/-)-fawcettimine, (+/-)-lycoflexine, (+/-)-fawcettidine, and (+/-)-lycoposerramine B have been accomplished through an efficient, unified, and stereocontrolled strategy that required sixteen, sixteen, seventeen, and seventeen steps, respectively, from commercially available materials. The key transformations involve: (1) a Diels-Alder reaction between a 1-siloxy diene and an enone to construct the cis-fused 6,5-carbocycles with one all-carbon quaternary center, and (2) a Fukuyama-Mitsunobu reaction to form the azonine ring. Access to the enantioselective syntheses of these alkaloids can be achieved by kinetic resolution of the earliest intermediate via a Sharpless asymmetric dihydroxylation.