摘要：

Selective oxidation of a 3-acyl derivative of methyl cholate to the 7-ketone can be accomplished in high yield with either N-bromosuccinimide or by Haslewood's procedure (aqueous potassium chromate added to an acetic acid solution buffered with sodium acetate). Potassium chromate in unbuffered aqueous acetic acid oxidizes 3-acyl derivatives of methyl cholate smoothly to the 7,12-diketones. The behavior on chromate oxidation of steroids having a free 3-hydroxyl group is variable; some are oxidized readily, others to a small extent and others (cholesterol) not at all. Improved techniques of selective oxidation and acylation have led to development of improved procedures for the preparation of methyl cholate, methyl cholate 3,7-diacetate, methyl cholate 7-acetate, chenodesoxycholic acid, methyl 3α,7α-diacetoxy-12-keto cholanate, methyl desoxycholate, methyl 3-carbethoxydesoxycholate and methyl 3α-carbethoxyoxy-12-keto-Δ 9(11)-lithocholenate. Carbethoxylation of bile acid derivatives is specific to the 3α-hydroxyl group, and in several instances 3-carbethoxy derivatives have proved advantageous as intermediates and in effecting separations and isolations. 7-Keto and 7,12-diketo derivatives of cholic acid have been isolated in several forms of unestablished nature.

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