Synthetic Transformations of Higher Terpenoids. XXXIII.* Preparation of 15,16-Dihydroisopimaric Acid and Methyl Dihydroisopimarate and their Transformations
2014
Kharitonov, Yu. V. | Shul’ts, E. E. | Shakirov, M. M.
Methods were proposed for preparing 15,16-dihydroisopimaric acid and its methyl ester. Oxidation of methyl dihydroisopimarate through the action of 3-chloroperbenzoic acid occurred with formation of 7,8-epoxy-derivatives and 7α-hydroxydihydrosandaracopimarate. The latter in addition to 7-oxotetrahydroisopimarate were formed through the action of t-butylhydroperoxide in the presence of MoCl₅. Oxidation of dihydroisopimaric acid or the ester by selenium dioxide in dioxane gave the corresponding 14α-hydroxy-derivatives. Pyridinium chlorochromate transformed 14α-hydroxydihydroisopimarate into a mixture of methyl esters of 7α-hydroxy-8,14-epoxyisopimaric, 7-oxo-8,14-epoxyisopimaric, 7-oxo-14-hydroxyisopimaric, and 7α-hydroxysandaracopimaric acids. Oximation of methyl 7-oxotetrahydroisopimarate by hydroxylamine hydrochloride in MeOH in the presence of NaOAc gave a mixture of the corresponding (Z)- and (E)-oximes. Beckmann rearrangement of the 7-(E)-oxime of methyl tetrahydroisopimarate through the action of thionylchloride led to tetradecahydrodibenzo[b,d]azepine.
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