Synthesis of 1α, 5α-cyclosteroids

Ren, Yi (1992) Synthesis of 1α, 5α-cyclosteroids. Masters thesis, Memorial University of Newfoundland.

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Abstract

Epoxidation of 4,4-dimethylcholesta-1,5-dien-3-one with m-chloroperbenzoic acid gave a mixture of the epimeric 5α, 6α-epoxy- and 5β, 6β-epoxy-4,4-dimethylcholest-1-en-3-one. Unexpectedly, the major product was found to be the 5β, 6β-epoxide, in contradiction to what had been reported by others. The unambiguous assignment of the structures of these epoxides was based upon ¹H NMR experiments and X-ray crystallographic analysis of the 5α, 6α-epoxide. In this thesis, the chemistry of the 5β, 6β-epoxide is described in the context of attempts at the synthesis of the corresponding 1α, 5α-cyclosteroids. -- The synthesis of a new 1α, 5α-cyclosteroid, 4, 4-dimethyl- 1α, 5α-cyclocholesta-3,7-dione, by lithium or ytterbium in liquid ammonia reduction of the bis-α, β-unsaturated ketone 4, 4-dimethylcholesta-1,5-diene-3,7-dione, is described. The chemistry of the reductive cyclization is discussed. The ¹H- NMR spectra of the mono- and dihydroxy derivatives of the 1α, 5α-cyclosteroid reveal an unusually high-field signal due to H-9. X-ray diffraction analysis of 7β-hydroxy-4, 4-dimethyl- 1α, 5α-cyclocholestan-3-one indicates that ring B of the steroid nucleus possesses a boat conformation, and that H-9 partially eclipses the cyclopropyl ring. An anisotropic ring current effect is postulated to account for the chemical shifts of H-9 in these cyclosteroids. The chemistry of these compounds are described. -- Various other attempts at the synthesis of 1a, 5a- cyclosteroids are also described.

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