Efficient Synthesis of (1S,5S)-4-Alkyl-6,6-dimethylbicyclohept-3-en-2-ones from (1R,5S)-(+)-Nopinone and Preparation of Some Chiral Building Blocks Suitable for the Asymmetric Synthesis

Article abstract of DOI:10.1021/jo00067a026

A general and convenient transformation of (1R,5S)-(+)-nopinone (1) into (1S,5S)-4-alkyl-6,6-dimethylbicyclo<3.1.1>hept-3-en-2-ones, i.e. (-)-verbenone (6a) as the simplest compound and its C(4)-alkyl homologs 6b-f, via (+)-apoverbenone (7) is developed and applied, starting with 6a,e, to the syntheses of (4R,5R)-1-acetoxy-4-isopropenyl-5-methyl-5-vinyl-1-cyclohexene (12a) and (4R,5S)- and (4R,5R)-1-acetoxy-5-(3-butenyl)-4-isopropenyl-5-methyl-1-cyclohexene (12b and 12c), in connection with a search for chiral building blocks suitable for the asymmetric synthesis.Preparation of 12a indicates the formal synthesis of the elemanoid sesquiterpenes (-)-β-elemenone and (-)-eleman-8β,12-olide