RATIONALE: Hypervalent iodine compounds are important and widely used oxidants in organic chemistry. In 2005, Ochiai reported the PhI-catalyzed alpha-acetoxylation reaction of acetophenone by the oxidation of PhI with m-chloroperbenzoic acid (m-CPBA) in acetic acid. However, until now, the most critical reactive alpha-lambda(3)-iodine alkyl acetophenone intermediate (3) had not been isolated or directly detected. METHODS: Electrospray ionization tandem mass spectrometry (ESI-MS/ MS) was used to intercept and characterize the transient reactive alpha-lambda(3)-iodine alkyl acetophenone intermediate in the reaction solution. RESULTS: The trivalent iodine species was detected when PhI and m-CPBA in acetic acid were mixed, which indicated the facile oxidation of a catalytic amount of PhI(I) to the iodine(III) species by m-CPBA. Most importantly, 3.H+ was observed at m/z 383 from the reaction solution and this ion gave the protonated alpha-acetoxylation product 4.H+ at m/z 179 in MS/MS by an intramolecular reductive elimination of PhI. CONCLUSIONS: These ESI-MS/ MS studies showed the existence of the reactive alpha-lambda(3)-iodine alkyl acetophenone intermediate 3 in the catalytic cycle. Moreover, the gas-phase reactivity of 3.H+ was consistent with the proposed solution-phase reactivity of the alpha-lambda(3)-iodine alkyl acetophenone intermediate 3, thus confirming the reaction mechanism proposed by Ochiai. Copyright (C) 2012 John Wiley & Sons, Ltd.
