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DOI: 10.1055/sos-SD-026-00532

Landais, Y.; Vincent, J. M.Science of Synthesis, (200526670.

The conversion of α-oxo imines and related compounds into the corresponding 1,2-diketones depends on the nature of the substituent on nitrogen. Standard acids, such as acetic, hydrochloric, and perchloric acids, are generally used to hydrolyze simple imines and nitrones under mild conditions. For example, treatment of 111, prepared by oxidation of aniline 110, with 60% perchloric acid at 0°C provides the corresponding 1,2-quinone 112 in excellent yield (Scheme 28).[‌80‌] A 6M solution of hydrochloric acid is used to hydrolyze α-oxo imine 113, obtained through nitrosation of the corresponding β-oxo ester, to give the α,β-dioxo ester 114.[‌81‌] A large number of oxidative methods have been developed for the conversion of oximes into ketones. Deoximation can be performed with excellent efficiency, using the DessMartin periodinane[‌82‌] or N-bromosuccinimide (e.g., conversion of 115 into 116, Scheme 28).[‌83‌] Other oxidants such as copper(II) nitrate,[‌84‌,‌85‌] chromi­um(VI) oxide,[‌86‌] or wet sodium bismuthate[‌87‌] supported on silica gel have been employed in conjunction with microwave irradiation. These reactions are characterized by a generally high yield and short reaction times. Another reagent that can be used instead of these Brønsted acids is aqueous sulfuric acid in methanol.[‌88‌] Boron trifluoridediethyl ether complex in dichloromethane is particularly useful when a nonaqueous medium is required.[‌89‌] O-Protected oximes are similarly converted into 1,2-diketones under reductive conditions using zinc in acetic acid.[‌90‌] Hydrazones are transformed into 1,2-diketones under acidic conditions (H2SO4 and HCl) or using oxidative conditions, i.e. copper(II) chloride or acetate.[‌91‌] Finally, semicarbazones are transformed into 1,2-diketones through treatment with wet antimony(III) chloride under solvent-free and microwave conditions, leading to the desired 1,2-diketones in high yield after only a few seconds.[‌92‌]

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