Cyclopropane 1-methyl-2,2-diphenyl

Cleavage Gem-dihalides and monohalides have been dehalogenated to chiral monohalides in the presence of alkaloids [397, 398]. l,l-Diphenyl-2-bromo-2-carboxyl (bromo or methyl carboxylate) cyclopropanes are cathodically debromi-nated in the presence of alkaloid cations with enantioselectivities up to 45% ee. A mechanism is proposed whereby the alkaloid is adsorbed at the Hg cathode, which protonates face selectively the carbanion generated by 2e reduction from the bromide [399]. 

A second example of the use of ionic chiral auxiliaries for asymmetric synthesis is found in the work of Chong et al. on the cis.trans photoisomerization of certain cyclopropane derivatives [33]. Based on the report by Zimmerman and Flechtner [34] that achiral tmns,trans-2,3-diphenyl-l-benzoylcyclopropane (35a, Scheme 7) undergoes very efficient (0=0.94) photoisomerization in solution to afford the racemic cis,trans isomer 36a, the correspondingp-carboxylic acid 35b was synthesized and treated with a variety of optically pure amines to give salts of general structure 35c (CA=chiral auxiliary). Irradiation of crystals of these salts followed by diazomethane workup yielded methyl ester 36d, which was analyzed by chiral HPLC for enantiomeric excess. The results are summarized in Table 3. 

Recently, the cyclopropanation of (Z)-4-benzyIidene-2-phenyl-5(4//)-oxazolone 621 with phenyldiazomethane was reported to give the spirocyclopropane, rac- 21 in very high yield. Subsequent ring opening and hydrolysis of rac- 21 generated frani-l-amino-2,3-diphenyl-l-cyclopropanecarboxylic acid, rac-828 (cadiPhe) (Scheme 7.256). This new, constrained phenylalanine analogue induces a y-tum in the sohd state when incorporated into model dipeptides. The enantiomers of the Al-Boc (Boc = tert-butyloxycarbonyl) methyl ester of 828 have been resolved by HPLC. 

PENTAMETHYL-, 56, 1 Cyctopentane, acetyl-, 55, 25 Cyclopentane, 1-cyano-l-phenyl-, 55, 94 Cyclopentane, methyl, 55, 62 Cyclopentanol p-toluenesulfonate, 55, 112 Cyclopentene, 56, 34, 58, 73 2-Cyclopenten-l-one, 2,5-dialkyl- 58, 62 CYCLOPENTENONES, 58, 56 Cyclopropane, 1 -acetyl-1 -phenyl-, 55, 94 Cyclopropane, 1, l-dibromo-2,2-diphenyl-, 56, 32... 

The first example of the rearrangement of a cyclopropyl radical to an allyl radical in solution was observed in the thermal decomposition of l-methyl-2,2-diphenylcyclo-propanecarbonyl peroxide The radical reacted by abstracting hydrogen from solvent or by rearranging to the l,l-diphenyl-2-methylpropenyl radical which dimerized to yield l,l,6,6-tetraphenyl-2,5-dimethyl-l,5-hexadiene (89). The proportion of dimeric product to that of cyclopropane is dependent on the solvent. If a good radical scavenger is used, such as chloroform, carbon tetrachloride or thiophenol, then only the unrearranged cyclopropane derivative is obtained. This is also the case when a radical trap such as iodine is added to a benzene solution. 

Controlled potential electrolysis of (-l-)-(5)-l-bromo-l-methyl-2,2-diphenyl-cyclopropane (51) in acetonitrile at —2.7 volts vs. SCE yielded the hydrocarbon... 

The controlled potential electrolysis of endo-7-bromo-exo-7-chlorobicyclo[4.1.0] heptane (31) and exo-7-bromo-endo-7-chlorobicycyclo[4.1.0]heptane (30) resulted in a mixture of exo-32 and endo-7-chlorobicyclo[4.1.0] heptane (33) in which the retention-inversion ratio was 2.6 1 in each case. Overall retention of configuration is the usual observation However, this need not always be the case, since by changing the substituent at the reductive center from methyl in bromo-l-methyl-2,2-diphenyl-cyclopropane (51) to a carboxyl or carbomethoxyl group, the resulting product was still optically active (30-40%) but the configuration was inverted... 

Walborsky and Rachon have also reported on the use of Rieke magnesium to obtain reaction with (S)-(+)-l-bromo-l-methyl-2,2-diphenylcyclopropane at —65°C to afford a chiral Grignard reagent that is 33-43% optically pure [73]. In 1961, Young and Walborsky [74] demonstrated that the reaction of chiral (S)-(+ )-l-bromo-l-methyl-2,2-diphenyl-cyclopropane (Table 5 1) with magnesium powder resulted in the formation of a chiral Grignard reagent as evidenced by the fact that on carbonation of the reaction mixture an optically active acid was obtained with an optical purity of approximately 12-18%. 

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. 

For all these codimerizations Pd(0) as well as Ni(0) catalysts can be used, preferred catalysts are Pd(PPh3)4 or mixtures of Ni(cod)2 and a arylphosphite in a molar ratio of 1 1. The less reactive diphenylketene-N-methylimine only reacts with methylene-cyclopropane to give cycloadducts in moderate yields [catalyst Pd(PPh3)J. Interestingly only the C=C double bond undergoes the cycloaddition giving 1-methylimino-3-methyl-5,5-diphenyl-2-cyclopentene 217). 

Among the several examples given, the reaction of ( )-(55,67 )-4-rert-butoxycarbonyl-3-ethylidene-5,6-diphenyl-3,4,5,6-tetrahydro-2//-morpholin-2-one (20) with the ylide from racemic (diethylamino)(methyl)(oxo)(phenyl)sulfonium tetrafluoroborate to give the cyclopropane derivative 21 in 82% yield with 100% diastereofacial selectivitycan be mentioned. 

Free-radical bromination of l-methyl-2-phenylcyclopropane (4) at — 78 °C followed by reduction of the products yields butylbenzene (5) and small amounts of 2-methyl- (6) and/or 1-methyl-1-phenylpropane (7). The light-induced addition of bromine to cis- and tranj-1,2-diphenyl-cyclopropane gave l,3-dibromo-l,2-diphenylpropane exclusively. The monophenyl deriva-... 

Methyl 2-(Diphenyl-hydroxy-methyl)-4-oxo-4-phenyl- 2134 Cyclopropane... 

Dehydroamino acids derived from (57 ,6S )-4-(terr-butoxycarbonyl)-5,6-diphenyl-2,3,5,6-tetra-hydro-4//-l,4-oxazin-2-onc are cyclopropanated with the ylide from [(diethylamino)methyl]-phenyljoxosulfonium tetralluoroborate in high chemical and optical yields. The products obtained can be transformed into enantiomerically pure (lS )-l-aminocyclopropanecarboxy-latesl04. Also, optically pure methyl (SS)-3,3-diphenyl-(4-tolylsulfinyl)propenoate reacts with dimethylsulfoxonium methylide to give the corresponding (l7 )-cyclopropane derivative105. 

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