Synthesis of (1α,7α,8β)-(±)-8-methyl-2-methylenebicyclo[5.3.0]dec- 5-en-8-ol. Structure revision of natural dictamnol

Abstract

The total synthesis of the title compound (±)-1 is described. The key step in the synthesis of this cis-fused trinor-guaiane is the base-induced and -directed rearrangement of the tosylate ester 4. Because of differences in the spectral data of synthetic (±)-1 and natural dictamnol, a trinor- guaiane isolated from Dictamnus dasycarpus TURCZ., a revised structure for the natural product is proposed. Nuclear Overhauser effect (NOE) difference experiments and a detailed investigation of the air-induced cyclization reaction of pregeijerene, isolated from Amyris diatrypa SPRENGEL, support the structure revision of natural dictamnol.