ETHANOL, 2-BROMO-1,2-DIPHENYL

If one compares the solvolyses of 2-bromo-l,l-diphenyl-4-(p-methoxyphenyl)-but-l-en-3-yne (57) and 4.4-diphenyl-1 -bromo-1 -(/ -mcthoxyphcny l)-buta-1,2,3-tricncs (58, X = Br) in aqueous ethanol (equation 21), the destabilization of the intermediate cation 59 by the large inductive effect of the triple bond as compared to its conjugative effect is evident42. Only in the case of 58 could the substitution product butatrienyl enol ether 60 be isolated in 40% yield, while it was only detected by UV and IR spectroscopy in the solvolysis product of 57. The faster observed reaction rate of 58 as compared to 57 was ascribed to a difference in their ground-state energies42. 

PyrazoUne-5-ones. Treatment of 2-bromo-l,3-diphenyl-l,3-propanedione (1) with methylhydrazine in ethanol at room temperature gives l-methyl-3,4-diphenyl-A -pyrazoline-5-one (2) in 56% yield. It is probably formed by a halohydrin rearrangement as indicated. 

Bromo-3-hydroxy-5,6-dimethylpyrazine and 2-bromo-5-hydroxy-3,6-diphenyl-pyrazine with phosphoryl chloride afforded 2,3-dichloro-5,6-dimethylpyrazine and 2,5-dichloro-3,6-diphenylpyrazine, respectively (817) and the bromo substituent in 2-amino-3-bromo-5,6-dimethylpyrazine and its p-aminobenzenesulfonyl derivative have been replaced by chlorine on treatment with aqueous hydrochloric acid in ethanol (812). 

Preparation by reaction of chromium trioxide with 6-bromo-4-methyl-2,3-diphenyl-7-iso-propylbenzofuran in boiling acetic acid, followed by saponificadon of the keto ester so formed [501 ], by action of potassium hydroxide in ethanol in a water bath for 1 h [812]. 

Czochralska [113] investigated the reduction of the optically active 2-phenyl-2-chloropropionic acid at a mercury cathode in acidic ethanolic solution. It was found that inversion took place during electrolytic reduction, and the yield of optically active product amounted to 77.2-92.2%. Annino and co-workers [112] investigated the electrolytic reduction on mercury of the optically active l-bromo-2,2-diphenylcyclopropanecarboxylic acid and its methyl ester, and also the reduction of l-bromo-l-methyl-2,2-diphenyl-cyclopropane in neutral, acidic, and alkaline ethanolic solutions. It was found that reduction of the acid took place with 26-35% inversion of the configuration in acidic solutions and with 31-38% retention in alkaline solutions. Reduction of methyl l-bromo-2,2-di-phenylcyclopropanecarboxylate took place with 30-56% inversion of the configuration irrespective of the composition of the solution, whereas reduction of l-bromo-l-methyl-2,2-diphenylcyclopropane took place with 21% retention. These results can be explained on the assumption that the molecule is subject to attack by electrons from the side of the halogen atom and that the whole stereochemistry of the process is determined by stereoselective reaction with proton donors of the free carbanion or of the carbanion screened by the electrode. 

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