Synthesis of 11,14-Diacetoxy-13-(acetoxymethyl)podocarpa-8,11,13-triene. Correction of Proposed Structure for Premnolal

Abstract Oxidation of 11-acetoxyabieta-8,11,13-triene, derived from methyl 11-methoxyabieta-8,11,13-trien-18-oate, with chromium trioxide afforded 11,15-diacetoxyabieta-8,11,13-trien-7-one and 11-acetoxy-13-acetylpodocarpa-8,11,13-trien-7-one (11) in a ratio of ca. 2 : 1. The acetyl compound 11 was converted into a quinone, 13-(hydroxymethyl)podocarpa-8,12-diene-11,14-dione (18), by a series of reactions : iodoform reaction, esterification, acetylation, sodium borohydride reduction, dehydration, catalytic hydrogenation, lithium aluminium hydride reduction, and oxidation with Fremy’s salt. Reductive acetylation of 18 produced 11,14-diacetoxy-13-(acetoxymethyl)-podocarpa-8,11,13-triene (2). The 1H NMR spectrum of 2 was different from that of 15-acetoxypremnol diacetate which was prepared from natural premnolal. Based on this fact a corrected structure of premnolal is proposed.