Asymmetric synthesis of (+)-nemorensic acid— revision of the stereochemistry of the pyrrolizidine alkaloid nemorensine
Abstract
(+)-Nemorensic acid, the necic acid constituent of the pyrrolizidine alkaloid nemorensine, is shown to be (2R, 3R,5S)-2-carboxy-2,3,5-trimethyltetrahydrofuranacetic acid by synthesis from (R)-(+)-β-citronellol, and a corrected structure for the parent alkaloid nemorensine is established by a single crystal X-ray analysis.