Desulfurization with nickel and cobalt boride: scope, selectivity, stereochemistry, and deuterium-labeling studies
摘要:
A variety of organosulfur compounds containing alkylthio and arylthio groups underwent reductive desulfurization under notably mild conditions when treated with nickel boride, generated in situ from nickel chloride hexahydrate and sodium borohydride in methanol-THF(3:1). Phenyl,chloro, and ester groups are not reduced under these conditions, while iodo, bromo, nitrile, aldehyde, ketone, cyclopropane, and olefinic functions are reduced either completely or partially. Deuterium-labeling studies indicate that the hydrogen that is incorporated into the product originates from both the sodium borohydride and the protic solvent, suggesting the intermediacy of dihydrogen. The epimers 3alpha- and 3beta-(phenylthio)cholestane afforded 3alpha- and 3beta-deuteriocholestane, respectively, demonstrating that the reaction proceeds with retention of configuration. The method may thus be employed for the stereospecific preparation of deuterated products from organosulfur compounds. Arguments are presented in support of a tentative mechanism involving an oxidative addition-reductive elimination sequence via a nickel hydride intermediate.
Desulfurization with nickel and cobalt boride: scope, selectivity, stereochemistry, and deuterium-labeling studies
摘要:
A variety of organosulfur compounds containing alkylthio and arylthio groups underwent reductive desulfurization under notably mild conditions when treated with nickel boride, generated in situ from nickel chloride hexahydrate and sodium borohydride in methanol-THF(3:1). Phenyl,chloro, and ester groups are not reduced under these conditions, while iodo, bromo, nitrile, aldehyde, ketone, cyclopropane, and olefinic functions are reduced either completely or partially. Deuterium-labeling studies indicate that the hydrogen that is incorporated into the product originates from both the sodium borohydride and the protic solvent, suggesting the intermediacy of dihydrogen. The epimers 3alpha- and 3beta-(phenylthio)cholestane afforded 3alpha- and 3beta-deuteriocholestane, respectively, demonstrating that the reaction proceeds with retention of configuration. The method may thus be employed for the stereospecific preparation of deuterated products from organosulfur compounds. Arguments are presented in support of a tentative mechanism involving an oxidative addition-reductive elimination sequence via a nickel hydride intermediate.
<i>o</i>-Nitrophenyl Sulfoxides: Efficient Precursors for the Mild Preparation of Alkenes
作者:Xiao Lu、Timothy E. Long
DOI:10.1021/jo902248z
日期:2010.1.1
to be efficient synthetic precursors of various alkene types. The elimination occurs in toluene and NaOAc to generate substituted and terminal alkenes. Alkene products were easily obtained in high purity due to the simultaneous precipitation of the o-nitrophenyl sulfenic acid byproduct. The methods described have practical applications for the preparation of unsaturated compounds under mild, thermolytic
protocol for the purple light-mediated anti-Markovnikov functionalization of alkenes with thiols. Crucial to the generation of the thiyl radical was the formation of a key photo-active complex. More than 30 thioether products were obtained, demonstrating tolerance towards different functional groups and scalability up to 5 mmol of alkene. Two different reaction conditions have been developed, varying