The enantioselective total synthesis of 12 carboxyeudesma 3,11(13) diene(1) was achieved starting from(-) dihydrocarvone in ten steps for the first time. The key steps mainly include the introduction of hydroxyl group into C 12 position of eudesmane by Vilsmeier chlorination and the generation of C3-C4 double bond into the eudesmane skeleton by elimination of halide.
14-Noreudesma-4,11-dien-3,9-diones′ analogues were treated with DDQ in dioxane and afforded the rearranged aromatic products. The similar compounds to eudesma-4,11-dien-3,9-diones had no reaction. 9-Actoxy-14-noreudesma-4,11-dien-3-ones, 9-actoxy-eudesma-4,11-dien-3-ones and their analogues yielded the normal 1,2-dehydro-products. The mechanism of the rearrangement was discussed.
(±)-1-Methyl-7-oxabicyclo[2.2.1]heptan-2-one (1) is a versatile chiral building block for terpenoids. It could be applied in total synthesis of eudesmanes, agarofurans and norcarotenoids. Compound (±)-1 was reduced to alcohol (±)-2. Compound (±)-2 was esterified with commercial available optically pure (S)-(+)-mandelic acid. The diastereomeric ester mixture was separated with preparative HPLC method. After oxidation of the saponified products of diastereomeric ester (+)-4 and (+)-5 respectively, both optically pure enantiomers of compound 1 were prepared for the first time in four steps with an overall yield of 70%. The absolute configurations of (+)-1 and (-)-1 were determined as (+)-(1R,4S)-1-methyl-7-oxabicyclo[2.2.1] heptan-2-one and (-)-(1S,4R)-1-methyl-7-oxabicyclo[2.2.1] heptan-2-one.
