Improved synthesis of 3-keto, 4-ene-3-keto, and 4,6-diene-3-keto bile acids.

Cholic and deoxycholic acids can be converted into 3-keto derivatives in 75-80% yield, by a four-step synthesis consisting of formylation, selective deformylation of the 3-formoxyl group, oxidation, then deformylation of the remaining formoxyl groups. The intermediate 3-keto formoxyl acids in this sequence were shown to be suitable starting compounds for the synthesis of 4-ene-3-keto acids, in 55-60% yield, via bromination, dehydrobromination, and deformylation. By extending the dehydrobromination reaction, the 7 alpha-formoxyl group of the intermediate 4-ene-3-keto-7 alpha,12 alpha-diformoxyl acid is also lost, hence providing a useful synthetic route to 4,6-diene-3-keto bile acids.