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Lithium-ammonia reduction of 10α-cholest-5, 7-dien -3β-ol (5h) gave the 5α-Δ⁷-olefins (5β:5α; 63:15). Perbenzoic acid oxidation of the diene (5h) gave 5, 6β-epoxy-5β, 10α-cholest-7-en-3β-ol (72c, 60%); 5β, 10α-cholest-7-en-3β,5, 6α-triol (70d, 25%); and 3β,6β-oxido-5α, 1Oα-cholest-7en-5-ol (71b, 12%). The ether (71b) is thought to arise via 5α, 6α-epoxide (72d) which was not isolated. Reduction of 3β,5-dihydroxy-5β, 10α-cholest-7-en-6-one (70f) with sodium borohydride-pyridine afforded the Δ⁷-6α-alcohol (70d; 14%). Lithium-ammonia reduction of enone (70f) gave 3β, 5-dihydroxy- and 3β-hydroxy-5β, 8α,10α-cholestan-6-one (84b, 32%; 84a, 4%), 5α, 10α-cholestane-3β, 6α-diol (85a, 14%), 5β, 8α, 10α-cholestane-3β, 6β-diol (84e, 30%), and 5β. 10α-cholest-7-ene-3β,5, 6β-triol (70h, 3%). Epoxidation of 5β, 10α-cholest-7-en-3β-ol (65c) gave the 7α, 8α-poxide (100) which under acidic conditions produced the 7-ketone (104). Lithium-ethylamine reduction of epoxide (100) gave the 5β, 8α, 10α: 7α-alcohol (112b; 50%) and the 5β, 8α, 10α:8-alcohol (113b, 12%). Base and additive shift values for angular methyl groups are estimated for the 5β, 8α, 10α and 5α, 10α-series and the dependence of these shifts on skeletal structure is discussed. |
