2.2- Diphenylcyclopropanecarboxylic acid

The retention of configuration at the exchange position was indicated by isolation of the pure (+)-(7 )-l-fluoro-2,2-diphenylcyclopropanecarboxylic acid, obtained by quenching the reaction mixture with carbon dioxide, and hydrolysis. Extensive use of a variety of cyclopropyllithium and magnesium derivatives, prepared by this method, is made in the synthesis of other metallacyclopropanes by metathesis reactions (vide infra). More recently, geminal dilithiocyclopropanes have been detected in the reduction of dihalocy-clopropanes by lithium 4,4 -di-r-butylbiphenyl and Li(Naph) radical anion , at low temperatures (-75 to -95 °C). 

The first chiral halides used by Walborsky and Young [43,44] were optically active 1 -bromo-1 -methyl-2,2-diphenylcyclopropane 18, 1 -chloro-1 -methyl-2,2-diphenylcyclopropane 12, and I-iodo-l-methyl-2.2-diphenylcyclopropane 14, the absolute configurations and optical purities of which were established [40,49] as were those of their derivatives, l-methyl-2,2-diphenylcyclopropane 13 and l-methyl-2,2-diphenylcyclopropanecarboxylic acid 17. 

When (S)-( 4-)-l-bromo-l-methyl-2,2-diphenylcyclopropane 18 was treated with a powdered magnesium-magnesium bromide mixture in refluxing tetrahydrofuran and the reaction mixture carbonated (Scheme 11), the resulting products l-methyl-2,2-diphenylcyclopropanecarboxylic acid 17 and l-methyl-2,2-diphenylcyclopropane 13 were optically active, with predominant retention of configuration. This was the first... 

Both trans- and c/j-2-phenylcyclopropanecarboxylic acid (6) can also be decarboxylated with lead tetraacetate in benzene at 80 C in the presence of a catalytic amount of pyridine and copper(II) acetate to give rran. -l,2-diphenylcyclopropane (8) in low yield (18-22%). When the oxidative decarboxylation of these carboxylic acids is carried out with lead tetraacetate in the presenee of iodine under irradiation ra ,v-l-iodo-2-phenylcyclopropane (9) is obtained as the sole product in 43% yield. Under identical conditions 2,2-diphenylcyclopropanecarboxylic acid leads to 2-iodo-l,l-diphenylcyclopropane (mp 45.5 C) in 57% yield. 

Oxidative decarboxylation of optically active l-methyl-2,2-diphenylcyclopropanecarboxylic acid (10) with lead tetraacetate in the presence of iodine leads to racemized 1-iodo-l-methy 1-2,2-diphenylcyclopropane (11) in 45% yield. Subjecting 10 to the Cristol-Firth modification of the Hunsdiecker reaction (bromine and mercuric oxide in carbon tetrachloride) leads to racemic 1-bromo-l-methyl-2,2-diphenylcyclopropane (12) however, the yield is poor (5 /o). ... 

Reduction of 1-Bromo-2,2-diphenylcyclopropanecarboxylic Acid (la), Methyl 1-Bromo-2,2-diphenylcy-clopropanecarboxalate (lb), and 1-Bromo-1-methyl-2,2-diphenylcyclopropane ( c) ... 

Hift02, S-(+)-2,2-Diphenylcyclopropanecarboxylic acid, 43B, 171 6H14O2, 2,3-Dicyclopropyl-1,4-naphthoquinone, 45B, 111 sH2oBrNO, (+)-trans-Chrysanthemic acid (p-bromoanilide derivative), 41B, 166... 

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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