Functionalization of unactivated carbons in 3α,6- and 3α,24-dihydroxy-5β-cholane derivatives by dimethyldioxirane

Direct remote functionalization of unactivated carbons by dimethyldioxirane (DMDO) was examined for 3α,6 and 3α,24-dihydroxy-5β-cholane derivatives. DMDO oxidation of stereoisomeric methyl 3α,6-diacetoxy-5β-cholanoates caused the direct, unexpected 14α- and 17α-hydroxylations, in analogy with that of the 5α-H analogs, regardless of the differences in stereochemical configuration of the A/B-ring junction and of the acetoxyl groups at C-3 and C-6. On the other hand, the ester derivatives of 3α,24-dihydroxy-5β-cholane with DMDO were transformed into the corresponding 5β-, 14α-, and 17α-hydroxy compounds, whereas the ether derivatives yielded the 5βhydroxy, 3-oxo, and C-24 oxidized products, accompanied by their dehydrated ones.