Phenacyl benzoate

Phenacyl benzoate condenses with acetamide in boiling xylene under boron trifluoride etherate catalysis to give a high yield of 2,4-diphenyloxazole in a general synthesis of diaryloxazoles (Scheme 7) <96T10131>. 

Product distributions and reaction conversions of several different photochemical systems, irradiated by conventional UV source and by EDL in a MW-UV reactor (Fig. 14.5), were compared to elucidate the advantages and disadvantages of a micro-wave photochemical reactor [90], Some reactions, e.g. photolysis of phenacyl benzoate in the presence of triethylamine or photoreduction of acetophenone by 2-propa-nol, were moderately enhanced by MW heating. The efficiency of chlorobenzene photosubstitution in methanol, on the other hand, increased dramatically with increasing reaction temperature. 

Cleavage of phenacyl esters (typical procedure)f To a solution of NaHTe (prepared by heating powdered tellurium (1.28 g, 10 mmol) and NaBH4 (0.75 g. 15 mmol) under Nj in DMF at 80-90°C for 30 min, and then cooling at room temperature) is added a solution of phenacyl benzoate (1.92 g, 8 mmol) in DMF (30 mL). An instantaneous reaction takes place and the mixture is stirred at room temperature for 20 min. The solvent is evaporated and the mixture poured into H2O (100 mL) and fdtered to remove the tellurium. The basic filtrate is washed with ether and then the aqueous solution is acidified with 6 N HCl and extracted with ether (3x50 mL). The ether extract is dried (MgS04) and evaporated to give benzoic acid (1.11 g (91%) m.p. 121-122°C). 

Although this substance is a weaker base than either sodium ethoxide or sodium phenoxide, it has much greater nucleophilic power. Sheehan and Daves- used it in dimethylformamide at or below room temperature to cleave sensitive ester functions (principally phenacyl) at the C—O bond to generate sodium salts of the corresponding carboxylic acids in good to excellent yield, as illustrated for phenacyl benzoate. The reagent is prepared by adding thiophenol to a molar proportion of... 

Correlation analyses of this type have also been carried out in connection with the kinetics of the reaction of ortho-substituted benzoate ions with para-substituted phenacyl bromides164 and of ortho-substituted benzoate ions with ethyl bromoacetate165. In all cases it is possible to include 0-SO2Me among the basic set of well-behaved substituents. 

Selective oxidation of polymethylpyrimidines. 2,4-Di- and 2,4,6-trimethyl-pyrimidines are selectively oxidized to 4-carboxylic acids by a slight excess of Se02 in pyridine. Yields are about 40-65%. This increased reactivity of a 4-methyl group of polymethylpyrimidines is also observed in reaction with ethyl nitrite in liquid ammonia to form 4-aldoximcs and with ethyl benzoate in the presence of KOC2H to form phenacyl derivatives. 

Two intermediates, (125) and (126), were proposed for the conversion of l-phenacyl-2-picolinium bromide into a mixture of the phenylindolizines (127 R = H) (Scheme 19). The enol betaine (126) has been shown to be an intermediate by an independent synthesis. It may be noted, however, that the benzoylation of the lutidine analogue at room temperature gave the enol benzoate (128) which on treatment with base yielded the expected indolizine (127 R = Me) (72CB2344). 

The reaction of a methyl group at the 6 or 8 position of 9-phenylpurine with benzaldehyde and ethyl benzoate in the presence of sodium hydride gave styryl and phenacyl purines. Conversion of Me into CHO was achieved by treatment with selenium dioxide in dioxan to give the purine carboxaldehyde <92CPB227>. 

Selectivity in Claisen type reactions is seen in the reaction of 2,4,6-trimethylpyrimidine with either ethyl benzoate or ethyl acetate. The reaction is at the 4-methyl group to furnish the 4-phenacyl or acetonyl product <55JA1559>. In the Mannich reaction the methylpyrimidine is warmed with formaldehyde and a secondary amine under acidic conditions in aqueous or alcoholic solution. In pyrimidines with strongly electron-releasing substituents, ring substitution may result. 4-Ethoxy-... 

As discussed above (Section 66.3), phenacyl ester radical anions fragment readily to phenacyl radicals and carboxylate anions. The radical anions of benzoate esters also fragment to carboxylate anions and alkyl radicals, and this process is faster if the alkyl radical is stabilized (3°, benzyhc). This concept has been applied successfully to the deoxygenation of carbohydrate alcohols by photoinduced electron transfer (PET) sensitization. For instance, irradiation of 38 in water/2-propanol, using a substituted... 

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