Swern and related oxidations

This is a good point to introduce some of the organic applications of higher-valent sulfur compounds. Dimethyl sulfoxide (DMSO) is well known in this regard it is not only an important polar, aprotic solvent but is also used to oxidize primary and secondary alcohols to the corresponding carbonyl compounds in a number of synthetic reactions, of which the Swern oxidation is the most important. The reagents used in the Swern oxidation are DMSO, oxalyl chloride, and an organic base such as triethylamine  

For primary alcohols, the reaction stops at the aldehyde stage, with no overoxidation to the carboxylic acid. A broad variety of functional groups are compatible with the reaction conditions. 

The oxalyl chloride serves to activate DMSO in the following way  

The intermediate so formed rapidly decomposes to a second more stable intermediate, the chlorodimethylsulfonium cation  

The chlorodimethylsulfonium cation reacts with the alcohol to yield an alkoxydimethylsu-fonium cation, which is common to all DMSO-mediated, Swern-type oxidations  

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Oxidation of Alcohols to Carbonyl Compounds via Alkoxysulfbnium Vlides The Moffatt, Swern, and Related Oxidations Thomas T. Tidwell 0-471-02933-0 3150.00... 

Tidwell, T. T. Oxidation of alcohols to carbonyl compounds via alkoxysulfonium ylides the Moffat, Swern, and related oxidations. Org. 

Sulfoxides (essentially DMSO) can be used for oxidation of alcohols to carbonyl compounds as in the Moffatt, Swern and related oxidations [237, 238]. These mild and useful processes proceed through an oxosulfonium salt. In the Pfitzner-Moffatt procedure the alcohol is treated with DMSO, DCC and anhydrous phosphoric acid. The proposed mechanism involves an alkylsulfonium ylide as an intermediate. 

Oxidation of Alcohols to Carbonyl Compounds with Activated Dimethyl Sulfoxide via Alkoxysulfonium Ylides. The Swern, Moffatt, and Related Oxidations... 

S.F. Martin and co-workers utilized a double Swern oxidation in their synthesis of ircinal A and related manzamine alkaloids. The advanced tricyclic did intermediate was first subjected to the Swern oxidation conditions at -78 °C to afford the corresponding dialdehyde in excellent yield. In the next step, the dialdehyde was exposed to excess Wittig reagent under salt-free conditions to form the two terminal alkenes. 

Mancuso, A. J. Swern, D. Activated Dimethyl Sulfoxide Useful Reagents for Synthesis Synthesis 1981,165-185. Mancuso, A. J. Brownfain, D. S. Swern, D. Structure of the Dimethyl Sulfoxide-Oxalyl Chloride Reaction Product. Oxidation of Heteroaromatic and Diverse Alcohols to Carbonyl Compounds /. Org. Chem. 1979, 44, 4148-4150. Mancuso, A. J. Huang, S-L. Swern, E. Oxidation of Long-Chain and Related Alcohols to Carbonyls by Dimethyl Sulfoxide Activated by Oxalyl Chloride J. Org. Chem. 1978, 45, 2480-2482. Omura, K. Swern, D. Oxidation of Alcohols by Activated Dimethyl Sulfoxide. A Preparative Steric and Mechanistic Study Tetrahedron 1978, 54, 1651-1660. 

In Chapter 24 we mentioned the Swern oxidation briefly as an excellent method of converting alcohols to aldehydes. We said there that we would discuss this interesting reaction later and now is the time. The mechanism is related to the reactions that we have been discussing and it is relevant that the Swern oxidation is particularly effective at forming enals from allylic alcohols, the Swern oxidation... 

Nucleophilic Attack at Halogen. This field of activity continues to be dominated by applications of well-known phosphine-positive halogen combinations. Alcohols can be oxidised to the related aldehydes and ketones under mild conditions by the DMSO-Ph3PX2 system, which provides an alternative to the Swern oxidation." The triphenylphosphine-iodine system has been... 

In the first step of this reaction sequence, the primary alcohol 21 is oxidized to the corresponding aldehyde 38 in a Parikh-Doering oxidation which is related to the Swern oxidation. In general, this type of oxidation is conveniently carried out by addition of a solution of pyridine-SOs complex in DMSO to a mixture of the alcohol, DMSO and NEts. It can be assumed that dimethyl sulfoxide and sulfur trioxide react to form 0-dimethylsulfoxonium sulfate 40, which then further reacts with primary alcohol 39 to give 0-alkyl dimethylsulf-oxonium intermediate 41. Then, sulfonium salt 42 is formed and subsequently deprotonated by NEts to give sulfonium ylide 43. Finally, an intramolecular p-elimination occurs to provide the desired aldehyde 44 and dimethyl sulfide. 

Similarly, 19-oxoaspidospermidine (581), synthesized by Gramain, Husson, and their collaborators, was oxidized by Swern s method to the related indolenine 622, which cyclized to 19-oxoaspidofractinine (640) when... 

This reaction is related to the Dess-Martin Oxidation, Swern Oxidation, and Pfitzner-Moffatt Oxidation. 

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