1β,19-cyclo-5α-steroids have been
synthesized by reductive cyclization of
3,17-dioxo-5α-androst-1-en-19-al with zinc in aqueous
acetic acid or lithium in ammonia. The major product from the zinc
reaction, the 19(R)-cyclopropanol, exists in equilibrium with
the 3-hemiketal; the minor product, the 19(S)-alcohol, is
isolated as the silyl ether and deprotected to give the
19(S)-cyclopropanol. The major product from the
lithium–ammonia reaction is the 19(S)-cyclopropanol.
Neither acid nor base treatment of the 19(R)- and
19(S)-alcohols gives evidence of their interconversion.
Structures are established by NMR measurements.
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Journal of the Chemical Society, Perkin Transactions 1
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