Synthesis and resolution of albicanic acid. Simple access to optically active drimane sesquiterpenes

Abstract

The synthesis of albicanic acid (±)-(2) and the resolution to its enantiomers (+)-(2) and (–)-(2) are described. Determination of their optical purity was by ¹H n.m.r. spectroscopy of the corresponding methyl esters (+)-(1) and (–)-(1) with Eu(dcm)₃. The absolute configuration of the acids (+)-(2) and (–)-(2) has been determined by transformation to their alcohols (–)-(5) and (+)-(5) and interrelation with the natural albicanol. An efficient formal total synthesis of both enantiomeric forms of three drimanic sesquiterpenes, drimenin (7), isodrimenin (8), and drim-7-ene-11,12-diol (9), presenting special synthetic interest, is reported, starting from the corresponding enantiomers of albicanic acid (2).