Acetophenones rearrangements

The addition of hexafluoroacetone, benzophenone, acetone and acetophenone to tetra-fcrr-butyldisilene proceeds similarly. The 2 + 2 adducts with acetone and acetophenone rearrange further (equation 24)45. 

As already mentioned, some byproducts are formed from these o-alkoxyphenyl ketones, one of which resembles the rearrangement that the o-t-alkylphenyl ketones undergo. The scheme below depicts these byproducts for o-ethoxy ketones the benzophenone undergoes only cyclization, whereas the acetophenone rearranges to a hemiketal and to a vinyloxybenzyl alcohol. 

The acid-catalyzed reaction of acetophenone with acyclic secondary amines results in the formation of the expected enamine and a rearrangement product. The latter product arises from the transfer of one of the amino N-alkyl groups to the cnamine s carbon to produce a ketimine (53a). 

The coupling of enamines with aromatic diazonium salts has been used for the syntheses of monoarylhydrazones of a-diketones (370,488-492) and a-ketoaldehydes (488,493). Cleavage of the initial enamine double bond and formation of the phenylhydrazone of acetone and acetophenone has been reported with the enamines of isobutyraldehyde and 2-phenylpropionalde-hyde. Rearrangement of the initial coupling product to the hydrazone tautomer is not possible in these examples. 

The first amination of a halogenopyridine involving a rearrangement was carried out by Levine and Leake in 1955 in an attempt to prepare 3-phenacylpyridine. When 3-bromopyridine (27, X = Br) was allowed to react with sodium amide in liquid ammonia in the presence of sodio-acetophenone, the reaction mixture obtained consisted chiefly of amorphous nitrogenous material from which only 10% of 4-aminopyridine (34, Y = NH2) and 13.5% of 4-phenacylpyridine were isolated. 

Chloro-5-nitrobenzaldehyde, -acetophenone, or -benzophenone derivatives treated with 2-aminothiophenol under alkaline conditions provided good yields of the corresponding dibenzo[(3,/][l,4]thiepins. Similar treatment of 2-chloro-3,5-dinitrobenzophenone (318) provided 58% of dibenzo[(3,/][l,4]thiepin 321 and 20% of phenothiazine 323. Its formation can be easily explain by the Smiles rearrangement of the initially formed intermediate 320 into diphenylamine derivative 322, followed by denitrocyclization reaction leading to the corresponding product of denitrocyclization 323 (Scheme 49). When the reaction was done in pyridine, only this product was isolated in 50% yield (57JCS3818). 

Yields of the di- r-methane rearrangement reaction strongly depend on substrate structure, and are ranging from poor to nearly quantitative. Acetone and acetophenone have been used as photosensitizers." ... 

C-H insertion also occurs in the reactions with acetone and acetophenone, presumably through the rearrangement of transient OH-substituted phosphi-ranes [87]. C-C insertions occur for diketones to give 45 and have been postulated to occur via initial 1,2-addition to the conjugated enol 44 [87]. Diimines 46 also undergo C-C insertions [88]. Based on a theoretical evaluation, the products 47 are considered to result from a 2,3-sigmatropic rearrangement of initial formed P,N-ylids. 

O-Acylated or mesylated oximes such as the ethyl carbonate of acetophenone-oxime 1772 react with TIS 17, with Beckmann rearrangement to the imidoyl iodide 1773, which adds phenylmagnesium bromide in situ to give 61% of the sec-... 

The availability of Nafion on silica has not only lowered the cost of the resin but also has made it versatile (Sun et al., 1997 Harmer et al., 1998). A number of industrially important reactions have been attempted, with considerable success, with these catalysts. Consider the Fries rearrangement of phenyl acetate to p-acetyl phenol (/t-hydroxy acetophenone). This has been accomplished by Hoelderich and co-workers (Heidekum, 1998). In the ca.se of alkylation of benzene with benzyl alcohol, Amberlyst-15 and p-toluene sulphonic acid are ineffective and Nafion on silica works well at 80 °C. 

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. 

The product profile thus reveals impressive parallels with the reaction of diphenyl-ketene, the carbon analogue of 9, with (p-methoxybenzal)acetophenone, in which, again under thermal conditions, both cycloadditions and fragmentation of the four-membered ring product25) occur. Overall, the rate or rearrangement 7- 9 appears to be more favorable by the thermal route than by the photochemical pathway. 

Baeyer-Villiger rearrangement and hydroxylation of acetophenone catalyzed by TS-I/H2O2 system... 

In contrast to the thermal solvolysis, a rearranged enol ether 45 (and also the hydrolysis product, acetophenone) is formed in addition to the unrearranged product 44. The rearrangement is more apparent in less nucleophilic TFE. The results are best accounted for by heterolysis to give the open primary styryl cation 46 (Scheme 8). This cation gives products of substitution 44 and elimination 30 by reaction with the solvent. Alternatively, 46 can rearrange to the a-phenyl vinyl cation 47 via 1,2-hydride shift, which gives rise to 45 and 30. 

Alkyl- and aryl-hydrazones of aldehydes and ketones readily peroxidise in solution and rearrange to azo hydroperoxides [1], some of which are explosively unstable [2], Dry samples of the p-bromo- and p-fluoro-hydroperoxybenzylazobenzenes, prepared by oxygenation of benzene solutions of the phenylhydrazones, exploded while on filter paper in the dark, initiated by vibration of the table or tapping the paper. Samples were later stored moist with benzene at —60°C to prevent explosion [3], A series of a-phenylazo hydroperoxides derived from the phenyl-or p-bromophcnyl-hydrazones of acetone, acetophenone or cyclohexanone, and useful for epoxidation of alkenes, are all explosive [4], The stability of several substituted phenylazo hydroperoxides was found to be strongly controlled by novel substituent effects [5],... 

The influence of radical stabilization on the outcome of the rearrangement reactions of a variety of dibenzobarrelenes has been evaluated178. A detailed analysis of the acetophenone-sensitized conversion of the cyano-substituted barrelenes into the corresponding semibullvalenes has been presented179. The outcome of the irradiation of the dibenzobarrelene 331 is dependent upon the excited state involved. Thus direct irradiation affords a cyclooctatetraene and sensitized irradiation converts it into the two... 

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