Synthesis of Methyl 3α,6β-Dihydroxy-5β-cholanate and the corresponding Ditosylate from Methyl 3α,6α-Dihydroxy-5β-cholanate

Methyl 3a,6a-dihydroxy-5/?-cholanate (2) was regioselectively oxidized at position 6 with chromium(VI) oxide in acetic acid into methyl 3a-hydroxy-6- keto-5/?-cholanate (3) and methyl 3,6-diketo-5/?-cholanate (4) in 70 % and 30 % yields, respectively. Stereoselective reduction of monoketone 3 with sodium borohydride in benzene-ethanol-water gave epimeric methyl 3a,6/?-di- hydroxy-5/?-cholanate (5) in 60 % yield. The same 3a,6^-diol (5) was obtained by reduction of the diketone (4). Tosylation of compound 5 with p-toluene- sulfonyl chloride in dry pyridine afforded 88 % methyl 3a,6/?-ditosyloxy-5/?-cho- lanate (7)