STEREOSELECTIVE SYNTHESIS OF (-)-TRACHELANTHIC ACID AND (+)-VIRIDIFLORIC ACID, NECIC ACID COMPONENTS OF PYRROLIZIDINE ALKALOIDS FROM A COMMON INTERMEDIATE

Diastereoselective reduction of a side-chain keto group in (2S,5R)-5-acetyl-2-(t-butyl)-5-isopropyl-1,3-dioxolan-4-one (5) with (i-Bu)2A1H in ether afforded (1'S,2S,5R)-2-(t-butyl)-5-(1'-hydroxyethyl)-5-isopropyl-1,3-dioxolan-4-one (6), while reduction of 5 with LiBH(s-Bu)3 in ether gave the (1'R)-isomer 7 predominantly. (-)-Trachelanthic acid (1) and (+)-viridifloric acid (2) were synthesized upon hydrolysis of 6 and 7, respectively.