Terpenoids-CV: transformation products of alantolactones

Abstract

Three lactones have been isolated from the roots ofInula racemosa and identified as alantolactone (I), isoalantolactone (II) and dihydroisoalantolactone (III) respectively. III was also prepared by partial reduction of II with NaBH₄, while on complete catalytic reduction, it formed tetrahydroalantolactone (IV). Amine adducts and methoxy derivs were prepared from II. The lactol VII and the diol VIII obtained from IV by controlled LAH reduction, when subjected to Huang-Minlon reduction, furnished the new crystalline monol, 8β-hydroxy eudesman (IX) and the diol VIII. The selinanone X, which is a convenient compound for the synthesis of 9-ketoeudesman (XX), was obtained from IX by oxidation with Jones' reagent. On Na/n-propanol reduction, X furnished the 8α-hydroxyeudesman (XIII) as a crystalline material. Lead tetraacetate oxidation of X yielded the rearranged keto acetate XXII. 9-Ketoeudesman (XX) was prepared from X via its furfurylidene deriv XXIII, followed by Wolff-Kishner reduction and ozonolysis. Tetrahedrocostic acid (XVIa) was obtained from the diol VIII by its oxidation to the keto-acid XV, followed by Wolff-Kishner reduction. The same sequence of reactions were carried out using III as the starting material to procure both the β- and α-unsaturated new crystalline monols (XXVII and XXIX) and the ketone XXVIII. A new interesting crystalline alcohol, 14-hydroxytetrahydroalantolactone (XXX) was prepared by hydroboration of III, oxidation of which with Jones's reagent yielded the lactone-acid XXXI.