A short and efficient degradation of the bile acid side chain. Some novel reactions of sulphines and α-ketoesters

11-Oxo-lithocholic acid acetate 5 is easily converted into the 23-sulphinyl derivative 6 by treatment with thionyl chloride and pyridine followed by addition of methanol. The sulphine group can be cleaved to the 23-ketone 9 in high yield using a variety of oxidising agents such as ozone, sodium hypochlorite, hydrogen peroxide or dinitrogen tetroxide or alternatively by exposure to acetic anhydride-sulphuric acid. With dinitrogen tetroxide, the reaction can be stopped at the oxime 10 stage. Finally aerial oxidation in the presence of an organic base and catalytic amounts of copper (II) salts degraded efficiently the keto-ester 9 into the 20-ketone 19. By operating under mild conditions, the intermediate 22-aldehyde 18 can be isolated in good yield.