Total syntheses of (+)-echinopine A and B: determination of absolute stereochemistry.
The first total syntheses of the novel 3,5,5,7-sesquiterpenoids (+)-Echinopine A (1) and B (2) were achieved. Thereby the proposed structures were confirmed, and the absolute stereochemistry was determined. The key features are (1) the stereoselective installation of the vinyl-moiety on the concave side of the bicyclo[3.3.0]octane core via Myers' [3,3]-sigmatropic rearrangement, (2) the finding that the substituent on the C7 position next to the ketone can be epimerized to the desired concave face under basic conditions, (3) the closure of the highly strained seven-membered ring via RCM, and (4) the unusual C2-homologation of a vinyltriflate with a ketene silyl acetal.
Magauer
Thomas
T
University of Vienna, Institute of Organic Chemistry, Wahringerstrasse 38, 1090 Vienna, Austria. thomas.magauer@univie.ac.at
Mulzer
Johann
J
Tiefenbacher
Konrad
K
D003500:Cyclization; D008968:Molecular Conformation; D012717:Sesquiterpenes / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D012717:Sesquiterpenes; C527602:echinopine A; C527604:echinopine B