Chemistry of the Podocarpaceae. XXIV. Ring-A modifications of Abieta- 8,11,13-trien-18-oic acid

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Abstract
A convenient route from abieta-8,11,13-trien-18-oic acid (10) to abieta5,8,11,13-tetraen-3-one (27) has been developed involving selective epoxidation of the alkene mixture (2) obtained by oxidative decarboxylation of the acid with lead tetraacetate. Treatment of the 3a,4a-epoxide (9) with lithium diethylamide gives a quantitative yield of the allylic alcohol (19). Brief treatment of this allylic alcohol with N-lithioethylenediamine gives the α, β-unsaturated alcohol (25), which on oxidation affords the enone (24). Methylation of the latter compound with methyl iodide and potassium t-butoxide in t-butanol yields abieta-5,8,11,13-tetraen-3-one (27) in 43% overall yield from the alkene mixture (2). Other reactions of the 3α, 4α-epoxide (9) are reported and discussed.

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