Synthesis of (−)-albrassitriol and (−)-6-epi-albrassitriol from (+)-larixol

Abstract

A novel synthesis of natural drimanic compounds, (−)-albrassitriol (2) and (−)-6-epi-albrassitriol (3), has been carried out starting from an easily available labdane diterpenoid, (+)-larixol (1). In a two-step procedure, (+)-larixol (1) was converted into 14,15-bisnorlab-7-ene-6,13-dione (9), which was then submitted to a Norrish type II photochemical degradation yielding drim-7,9(11)-diene-6-one (10), whose treatment with OsO₄ led selectively to the formation of drim-7-ene-9α,11-diol-6-one (12). The same compound was obtained by selective epoxidation of the C(9)–C(11) double bond in drim-7,9(11)-diene-6-one (10) with monoperphtalic acid. Treatment of the resulting mixture of α- and β-epoxides (13 and 14) with HClO₄ yielded drim-7-ene-9α,11-diol-6-one (12). Reduction of the C6-carbonyl group in drim-7-ene-9α,11-diol-6-one (12) with LiAlH₄ afforded (−)-albrassitriol (2) and (−)-6-epi-albrassitriol (3), 12.4% and 13.6% overall yields, respectively.

Keywords:

• larixol
• 14,15-bisnorlabene-6,13-diones
• photochemical degradation
• drim-7,9(11)-diene-6-one
• (−)-albrassitriol
• (−)-6-epi-albrassitriol

Acknowledgements

The support from the Project no. 264115 (STREAM) in the frame of the EU funded FP7-REGPOT-2010-1 call is acknowledged by the authors from the “Petru Poni” Institute.