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Parikh–Doering oxidation
The Parikh–Doering oxidation is an oxidation reaction that transforms primary and secondary alcohols into aldehydes and ketones, respectively.〔Tidwell, T. T. ''Org. React.'' 1990, ''39'', 297. 〕 The procedure uses dimethyl sulfoxide (DMSO) as the oxidant, activated by the sulfur trioxide pyridine complex in the presence of triethylamine base.
The reaction can be run at mild temperatures, often between 0 °C and room temperature, without formation of significant amounts of methylthiomethyl ether side product. The following example from the total synthesis of (–)-kumausallene by P.A. Evans and coworkers illustrates typical reaction conditions:
==Mechanism==
The first step of the Parikh–Doering oxidation is the reaction of dimethyl sulfoxide (DMSO), which exists as a hybrid of the resonance structures 1a and 1b, with sulfur trioxide (2), giving intermediate 3. Nucleophilic attack by alcohol 4 and deprotonation by pyridine (5) gives intermediate 6, an alkoxysulfonium ion associated with the anionic pyridinium sulfate complex.
The addition of at least two equivalents of base deprotonates the alkoxysulfonium ion to give sulfur ylide 7 and removes the pyridinium sulfate counterion. In the last step, the ylide goes through a five-membered ring transition state to give the desired ketone or aldehyde 8, as well as an equivalent of dimethyl sulfide.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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