Jervine—XIII : C/D ring cis-trans equilibria in tetrahydrojervine derivatives with open ring e

Abstract The levoratatory acetolysis product IV of tetrahydrojervine (III) and the dextrorotatory isomer formed from it on treatment with alkali and reacetylation 4 have been recognized, respectively, as the C/D cis -linked 13α-epimer Va and C/D trans -linked 13β-epimer Vla. In both compounds the 17a-methyl group is β-oriented. In alkaline methanol-tetrahydrofuran solution at 22° equilibrium is reached with 81% of the C/D trans -compound present. Configuration assignments (C-13, C-17) have been made on the basis of similar equilibrium studies for the 16,17-dihydro derivative VIIa (C/D cis ) formed in the catalytic reduction of Va, 4 and for the two dihydro products VIII and IXa (C/D trans ) obtained in the same manner from VI. 4 The results of this study serve to illustrate again the importance of conformational factors for the position of the cis-trans equilibrium in Δ 5 -hydrinden-1-one and hydrindan-1-one systems. They also allow to assign the α-configuration to the hydrogens at C-1 and C17a in tetrahydrojervine (III).