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
作者:Shoujiro Ogawa、Takashi Iida、Takaaki Goto、Nariyasu Mano、Junichi Goto、Toshio Nambara
DOI:10.1039/b314965j
日期:——
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 (5β)-3-oxobile acids. Using the DCP-N-oxide/Ru-porphyrin/HBr system, 5β-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 5β-position allowing for the competitive (20S)-20-oxyfunctionalization, subject to electronic constraints. A variety of novel 5β-hydroxylation and (20S)-24,20-γ-lactonization products, as well as their double-oxyfunctionalization and dehydration products, were obtained in one-step. The alkaline hydrolysis of the γ-lactones gave the corresponding stereoselective (20S)-20-hydroxy-carboxylic acids.
由 2,6-二氯吡啶 N-氧化物 (DCP N-氧化物) 作为氧供体和 (5,10,15,20-四三甲苯基卟啉) 钌 (II) 羰基络合物 (Ru-卟啉) 和 HBr 作为氧供体诱导的远程氧官能化检查了催化剂的一系列(5β)-3-含氧胆酸的甲酯-全乙酰化衍生物。使用 DCP-N-氧化物/Ru-卟啉/HBr 系统,由于空间位阻,5β-羟基化主要用于具有 12-乙酰氧基取代基的底物,但 7-乙酰氧基取代基的存在降低了 5β-位置的反应性允许竞争性(20S)-20-氧官能化,但受电子限制。一步获得了多种新型5β-羟基化和(20S)-24,20-γ-内酯化产物及其双氧官能化和脱水产物。 γ-内酯的碱性水解得到相应的立体选择性(20S)-20-羟基-羧酸。