Transition-metal-catalyzed hydrogen-transfer reactions have been used for the conversion of alcohols into benzimidazoles and aldehydes into benzoxazoles and benzothiazoles.
The oxidation of alcohols to their corresponding carbonyl compounds is a frequently employed fundamental organic transformation in synthetic laboratories and the chemical industry. 1 One of the most historic and widely used methods for alcohol oxidation involves the activation of dimethylsulfoxide (DMSO) by a variety of electrophilic reagents such as oxalyl chloride (Swern oxidation), dicyclohexylcarbodiimide (Pfitzner-Moffat), SO 3 .pyridine (Parikh-Doering), trifluoroacetic acid anhydride (Omura-Sharma-Swern) and N-chlorosuccinimide (Corey-Kim oxidation with dialkyl sulfide). 2 Among these DMSO-activation methods, Swern oxidation has regularly been the default pathway due to its consistent efficiency over a broad range of substrates. 2 The original Swern oxidation employed oxalyl chloride to form the reactive chlorodimethylsulfonium chloride, which subsequently reacted with alcohols and bases to give the carbonyl compounds and dimethyl sulfide. 3 The activation of DMSO by oxalyl chloride is strongly exothermic and violently generates toxic gases such that it has to be carried out at very low temperature in a well-ventilated area. 2-4 Furthermore, oxalyl chloride itself is a volatile toxic reagent that can be difficult to handle. There have been several studies investigating other chloride-bearing reagents for the replacement of oxalyl chloride in Swern-type oxidation reactions, most notably cyanuric chloride 4 and triphenylphosphine dichloride. 1 These reagents consist of reactive chlorides bonding to a heterocycle (cyanuric six-membered ring) or heteroatom (phosphorus in phosphine dichloride). Herein, we report the use of 1,1-dichlorocycloheptatriene (1) (Scheme 1), a simple chlorinated hydrocarbon, as a new DMSO activator for efficient Swern-type oxidation of a broad range of alcohol substrates under mild reaction conditions.
A ruthenium-catalysed oxidation of alcohols by hydrogen transfer has been coupled with organocatalysed condensations using pyrrolidine or piperidine, to give a,b-unsaturated esters and nitroalkenes. Reactions proceed with high (E)-selectivity and provide an efficient and straightforward route to a,b-unsaturated compounds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.