Terpenoids. Part 7. Diequatorial opening of 2,3-epoxides of ent-kauranes and ent-gibberellanes

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Abstract
Reduction of ent-2α,3α-epoxykaur-16-en-19-ol (1) by hydride to the 2-equatorial alcohol (4) is attributed to participation by the 19-hydroxy-group, since the 19-tetrahydropyranyl ether (2) and the 4.4-dimethyl epoxide (24) are reduced normally to the corresponding 3-axial alcohols (7) and (26) respectively. Reduction of ent-2β,3β-epoxykaur-16-en-19-ol (13) and the 19-tetrahydropyranyl ether (14) by hydride gave the 3-equatorial alcohol (19) and the 19-tetrahydropyranyl ether (23) respectively. Analogously, acidic hydrolysis of the ent-2β,3β-epoxides (30) and (31) in the ent-kaurane series, and of (40) and (41) in the ent-gibberellane series, afforded the diequatorial 2,3-diols. The abnormal opening of these ent-2β,3β-epoxides is attributed to the steric effect of the adjacent ent-4α-methyl group.

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