Acetophenones Acetoxylation

Acetophenones, aliphatic and cyclic ketones were a-acetoxylated by DIB in acetic acid-acetic anhydride, in the presence of sulphuric acid, in moderate yield some / -diketones were similarly acetoxylated at the methylene carbon. The more reactive trimethylsilyl ethers reacted at room temperature without acid catalysis, with retention of their silyl group the products came either from substitution of the vinylic hydrogen or from bis acetoxylation of the double bond. 

A study of the catalytic a-acetoxylation reaction of acetophenone by electrospray ionization tandem mass spectrometry (ESI-MS/MS) has confirmed the mechanism shown in Scheme 4.2. In particular, the trivalent iodine species was detected when iodobenzene and mCPBA in acetic acid were mixed, which indicated the facile oxidation of a catalytic amount of Phi to the iodine(III) species by mCPBA. Most importantly, the protonated alkyliodonium intermediate 3 (R = Ph, = H) was observed at m/z 383 from the reaction solution and this ion gave the protonated a-acetoxylation product 1 at m/z 179 in MS/MS by an intramolecular reductive elimination of Phi [17]. 

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