Oxetane from A-nor-steroides: 2-alpha, 5-oxido-A-nor-5-alpha-cholestane, 2-beta, 5-oxido-A-nor-5-beta-cholestane and 2-alpha-ethyl-2-beta,2'-oxido-A-nor-5-alpha-cholestane

Treatment of 2β-tosyloxy-A-nor-5α-cholestane-5-ol ( 2 ) with t-butoxide in t-butanol gave 2α, 5-epoxy-A-nor-5α-cholestane ( 3 ) in quantitative yield. When A-nor-5β-cholestane-2α, 5-diol ( 4 ) was treated with tosyl chloride in pyridine 2β-chloro-A-nor-5β-cholestane-5-ol ( 7 ) and 2α-tosyloxy-A-nor-5β-cholestane-5-ol ( 8 ) were obtained. Whereas the chloride 7 was resistant to t-butoxide the tosylate 8 was transformed into an 1 : 1 mixture of 2α, 5-epoxy-5β-cholestane ( 10 ) and 2ξ-t-butoxy-A-nor-5β-cholestane-5-ol ( 11 ). In 2α-tosyloxy-A-nor-5α-cholestane-5-ol ( 12 ) substitution occurred as the only reaction. Both oxetanes 3 and 10 isomerize after heating above 50° and in polar or protic solvents to form A-nor-Δ³⁽⁵⁾-cholestene-2α-ol ( 6 ) and -2β-ol ( 14 ) respectively. Also, 2, 5-diols are encountered. 2α-Ethyl-2β, 2′-epoxy-A-nor-5α-cholestane ( 23 ) was synthesized starting from A-nor-5α-cholestane-2-one ( 17 ). The intermediates were the ester 16 , the diol 18 , the hydroxy-tosylate 19 and the chlorhydrin 20 . The spirocyclic oxetane 23 was reduced by LiAlH₄ in dioxane (not in ether). By chromatography on silica gel 23 was isomerized to the homoallylic alcohol 21 and transformed into 2-methylene-A-nor-5α-cholestane ( 24 ) by fragmentation. The IR. and NMR. spectra of the new oxetanes were compared with those of a series of known oxetanes.