The remote-oxyfunctionalization of unactivated carbons in (5β)-3-oxobile acids by 2,6-dichloropyridine N-oxide catalyzed by ruthenium–porphyrin and HBr: a direct lactonization at C-20

• Published in: Organic & biomolecular chemistry Vol. 2; no. 7; pp. 1013 - 1018
• Main Authors: Ogawa, Shoujiro, Iida, Takashi, Goto, Takaaki, Mano, Nariyasu, Goto, Junichi, Nambara, Toshio
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 07.04.2004
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; ALCOHOLS; METABOLITES; STEROIDS; HIGHLY EFFICIENT OXIDATION; HYDROXYLATION; ALKANES
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/B314965J

Remote-oxyfunctionalization induced by 2,6-dichloropyridine N-oxide (DCP N-oxide) as an oxygen donor and a (5,10,15,20-tetramesitylporphyrinate) ruthenium(II) carbonyl complex (Ru-porphyrin) and HBr as catalysts was examined for a series of methyl ester-peracetylated derivatives of (5beta)-3-oxobile acids. Using the DCP-N-oxide/Ru-porphyrin/HBr system, 5beta-hydroxylation predominated for the substrates having a 12-acetoxyl substituent due to steric hindrance, but the presence of a 7-acetoxyl substituent decreased the reactivity of the 5beta-position allowing for the competitive (20S)-20-oxyfunctionalization, subject to electronic constraints. A variety of novel 5beta-hydroxylation and (20S)-24,20-gamma-lactonization products, as well as their double-oxyfunctionalization and dehydration products, were obtained in one-step. The alkaline hydrolysis of the gamma-lactones gave the corresponding stereoselective (20S)-20-hydroxy- carboxylic acids.