Acetophenone oxidative rearrangement

The ready availability of chalcones, from aldol condensation of acetophenones and benzaldehydes, makes this oxidative rearrangement a useful synthetic entry to isoflavone targets. The isoflavone products may be further elaborated to isoflavanones, isoflavans, pterocaipans and coumestones, broadening the scope of this method. 

FIGURE 6.42 Oxidation of 3-oxa-chromanol 58 in the presence of 1 equivalent of water mechanistic study hy means of selectively deuterated starting material. The initially formed ortho-quinone dimethide 63 rearranges into styrene derivative 64, which then reacts with water to provide acetophenone 61. 

Hayashi and his co-workers investigated the reactions of 2-substituted quinoxaline 4-oxides with ketones.210-212 2-Phenylquinoxaline 4-oxide (193) yields 2-phenyl-3-phenacylquinoxaline 4-oxide (203) with acetophenone and sodamide. However, 2-cyanoquinoxaline 4-oxide under these conditions yields cu-(3,4-dihydro-3-oxo-2-quinoxalinyl)aceto-phenone (204) by displacement of the cyano group by the ketone carbanion and rearrangement of the N-oxide.212... 

Many reactions of ketones were performed with methanolic DIB in either an acidic or alkaline environment. When DIB is dissolved in methanol (or other alcohols) an exchange with acetate takes place, so that the reacting species may be PhI(OMe)OAc or PhI(OMe)2 the latter is actually an isolable compound [12]. Oxidation of methanol at room temperature is negligible. Acetophenones react with DIB in methanol-sulphuric acid affording mixtures of a-methoxyacetophenones (minor products) and rearranged esters. A solvent change from methanol to... 

The Baeyer-Villiger rearrangement of cyclohexanone and acetophenone with TS-I/H2O2 proved to be poorly selective [117]. Notably, Ti-P and Sn-P have different chemoselectivities in the oxidation of unsaturated ketones, leading selectively to corresponding epoxides and lactones, respectively [118]. The different oxidation pathways were attributed to the preferential adsorption of hydrogen peroxide on Ti-sites and of the carbonyl group on Sn-sites. 

Anodic oxidation of n-alkanes in acetonitrile results in mixtures of A -s-alkylacetamides but skeletal rearrangement of the intermediate i-carbenium ions is not observed. Aromatic compounds can undergo direct acetamidation in the ring. Thus, acetophenone, which normally undergoes electrophilic aromatic substitution at the meta position, affords the o- and p-acetamides (Scheme 44). Anthracene is cleanly converted into the acetamide (84) when the reaction is performed in the presence of TFAA as water scavenger (equation 41). ... 

Aside from thallation, trivalent thallium is best known as a versatile oxidant in organic chemistry many of the reactions proceed with unique rearrangements. Let us first consider one that does not involve rearrangement. Thus, thallium(III) triflate (see Section 1.14 for the structure of the triflate anion), which may be obtained from the more common thallium(III) nitrate by treatment with trifluoromethanesulfonic (triflic) acid in DMF, oxidizes acetophenone to its a-trifluoromethanesulfonyloxy derivative ... 

Apparently, the intermediate O-vinyl oxime rearranges to nitrone A [328], which is further fused with acetophenone to generate triene nitrone B (Scheme 1.156). Electrocyclization of the latter gives dihydropyridine-N-oxide C, which rearranges in N-hydroxydihydropyridine D. 1,4-Abstraction of methanol from pyridine D leads to 2,4,6-triphenylpyridine via the intermediate 1,4-biradical E (analog of 1,4-benzoid Bergman biradical [329,330]). 

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