A comparative study of remote oxy-functionalization of unactivated carbons in 5 beta-steroids by dimethyldioxirane and 2,6-dichloropyridine N-oxide ruthenium-porphyrin HBr

Remote oxy-functionalization of methyl 3alpha-acetoxy- and 3-oxo-5beta-cholan-24-oates with 2,6-dichloropyridine (DCP) N-oxide catalyzed by (5,10,15,20-tetramesitylporphyrinate) ruthenium (II) carbonyl complex [Ru(TMP)CO] and HBr was compared with that with dimethyldioxirane (DMDO). Treatment of the 5beta-steroids with DMDO afforded the corresponding 5beta- and 17alpha-monohydroxylated and 5beta,14alpha- and 5beta,17alpha-dihydroxylated compounds. On the other hand, the corresponding 20S-mono- and 5beta,20S-dioxygenated derivatives (as the gamma-lactones), along with 5beta-hydroxy compounds, were found to be the major oxidation products of the 5beta-steroids with the DCP N-oxide / Ru(TMP)CO / HBr system. Both the reagents oxidized unactivated methine carbons stereoselectively, but the degree of regioselectivity depended upon the oxidants employed and the structure of the hydroxyl-protecting groups at C-3 (acetoxyl or carbonyl) of the substrates.