1 -Iodo-1 -methyl-2,2-diphenylcyclopropan

The nature of the lithium surface is important. Varying the particle size of the lithium dispersion from 25 pm with a surface area of 2782 cm to 150 pm with a surface area of 464 cm reduced the optical purity of the resulting acid by nearly 50%. It was also demonstrated that the amount of sodium impurity in the lithium dispersion had a significant effect not only on the stereochemical results of the metallation reaction but also on the reactivity of the metal surface itself. For example, reaction of chiral l-iodo-2,2-diphenylcyclopropane with 25 pm lithium dispersions containing 0.002 %, 0.02 % and 1 % sodium yielded after carbonation l-methyl-2-cyclopropanecarboxylic acid (99) with optical purities of 13 %, 16% and 36%, respectively. The increase in optical purity with increase in sodium content may be a consequence of lowering the ionization potential of the metallic surface . ... 

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. 

A solution of 4.76 grams of 2,2-diphenylcyclopropane carboxylic acid, [a] —128°, in 40 ml. 0.75M KOH was added to a 0.15M solution of K3Co(CN)r,H in four portions over a period of 30 minutes. After an additional reaction time of 45 minutes, 90% of the acid, [a] —115°, was recovered. Optically active 1-bromo- and l-iodo-l-methyl-2,2-diphenyl-cyclopropanes (55) could not be reduced. 

Racemization. Optically active 1-bromo-l-methyl-2,2-diphenylcy-clopropane, l-iodo-l-methyl-2,2-diphenylcyclopropane, and l-bromo-2,2-diphenylcyclopropane carboxylic acid were prepared to study the mechanism of alkane formation by hydrido complex. While the first two substrates could not be reduced, the a-bromo acid absorbed 87 mole % of hydrogen, being converted into optically inactive acid (Reaction 18). A sample of the optically active acid retained its configuration under reaction conditions, indicating that a symmetrical intermediate was formed at some stage of the reduction. 

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). ... 

Methyl-2,2-diphenylcyclopropanoylperoxide (17) is transformed into 1-chloro- and 1-iodo-l-methyl-2,2-diphenylcyclopropane (18, X = Cl, I) by heating in carbon tetrachloride or in a solution of iodine in carbon tetrachloride, respectively, albeit in poor yield.Decomposition of the (-)-(/ )-peroxide in tetrahydrofuran leads to 2-methy 1-1,1-diphenylcyclo-propane (18, X = H). In all cases complete racemization occurs. 

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