19(R/S)-Hydroxy-5β,19-cyclosteroids
have been synthesised from the 19-formyl 4-en-3-one by reductive
cyclization with zinc in aqueous acetic acid. Treatment of the aldehyde
with lithium in liquid ammonia also gave the
19(R)-hydroxy-5β,19-cyclosteroid together with
the 17β-hydroxy analogue. The 19(R)-alcohol is
isomerized to the 19(S)-alcohol in either dilute acidic or
basic media via the 3-hydroxy-3,5-cyclosteroid. The
19(S)-alcohol is in equilibrium with its 3-hemiketal.
Treatment
of the 19(R)-alcohol with methanolic HCl gave the
19(R)- and 19(S)-methyl ethers, the 3-methyl ether
19-ketal and the
3α-methoxy-3β,5β-
cyclosteroid. Further rearrangements of the 19(R)- and
19(S)-alcohols take place on more vigorous treatment with acid
or base to give cyclopropanol ring-opened aldehydes including a
5β-methyl-A-norsteroid. Metal hydride reduction of the
3-ketone in the 19(R)-alcohol gave only the
3β-alcohol whereas the 19(S)-alcohol gave both
the 3α- and 3β-alcohols. Acid treatment of
the 3β-alcohols gave products with retention of
configuration at C-5 and C-19 while base-catalysed ring opening gave
inversion at C-5. Ring opening mainly involved breaking of the
5,19-bond, however, the 19(S)-alcohol also resulted in
10,19-bond cleavage. Structures were established by NMR
measurements.
19(R/S)-Hydroxy-5β,19-cyclosteroids 是由 19-formyl 4-en-3-one 在
乙酸水溶液中与
锌发生还原环化反应而合成的。在液
氨中用
锂处理醛,也得到了 19(R)-羟基-5δ²,19-环甾烷和 17δ²-羟基类似物。在稀酸性或碱性介质中,19(R)-醇通过 3-羟基-3,5-环甾烷异构化成 19(S)-醇。用
甲醇盐酸处理 19(R)-
乙醇可得到 19(R)-和 19(S)-
甲醚、3-
甲醚 19-酮和 3δ-甲氧基-3δ²,5δ-环甾烷。19(R)-和 19(S)-醇在酸或碱的强力处理下发生进一步重排,生成
环丙醇开环醛,包括 5δ-甲基-A-正甾烷。
金属
氢化物还原 19(R)-醇中的 3-酮只得到 3δ-醇,而 19(S)-醇同时得到 3δ-和 3δ-醇。对 3δ-醇进行酸处理后得到的产物保留了 C-5 和 C-19 的构型,而碱催化的开环反应则使 C-5 发生反转。开环主要涉及 5,19-键的断裂,但 19(S)-醇也会导致 10,19-键的断裂。结构是通过核磁共振测量确定的。