A comparative study of remote oxy-functionalization of unactivated carbonsin 5β-steroids by dimethyldioxirane and 2,6-dichloropyridineN-oxide/ruthenium-porphyrin/HBr

Abstract

Remote oxy-functionalization of methyl 3α-acetoxy- and 3-oxo-5β-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 5β-steroids with DMDO afforded the corresponding 5β- and 17α-monohydroxylated and 5β,14α- and 5β,17α- dihydroxylated compounds. On the other hand, the corresponding 20S-mono- and 5β,20S-dioxygenated derivatives (as the -lactones), along with 5β-hydroxy compounds, were found to be the major oxidation products of the 5β-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.