1 -Chloro-2,3 -diphenylcyclopropane

Only the methoxy- and chloro-compounds (38, 3 ) exhibit large deviations between calculated and observed rotations. In general, the 1,1-diphenylcyclopropanes XVIII have rather large optical rotations ( [ ]d > 90°). Inspection of Table 3 reveals that the molar rotations of XVIII are almost entirely due to helix optical activity ( 0 q > 0 d ). This is in contrast to an earlier assumption which has attributed optical rotations of XVIII to atomic asymmetry. Further comparisons between calculated and observed optical rotations of complex cyclopropanes I are presented in Table 4. 

These observations are supported by the findings that the thermal decomposition of t-butyl (-f-)-(S)-l-chloro-2,2-diphenylcyclopropanepercarboxylate (28) in tetrahydrofuran resulted in completely racemic l-chloro-2,2-diphenylcyclopropane (29)". ... 

The thermal decomposition of ( —)-(R)-methyl-2,2-diphenylcyclopropanoyl peroxide, ( + )-(R)-48, in pure carbon tetrachloride yielded, besides the expected ( )-l-chloro-l-methyl-2,2-diphenylcyclopropane (52), a 2% yield of ( + )-(S)-l-methyl-2,2-... 

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. 

Dimethyl l-Chloro-3,3-diphenylcyclopropane-tcflns-l,2-dicarboxylate (1) Typical Procedure ... 

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. 

In hindered or strained systems the yields are more variable. Thus, the yield of methylene product from 1-chloro-l-methyl-2,2-diphenylcyclopropane was only 39%. ° In a series of methylenecyclopropanes containing a bicyclic system with aryl bridgehead substituents, the yields in some cases were very poor (Table 1). In the absence of such substituents, however, the yields are generally very good. Thus, a 78% yield of pure 7-methylenebicyclo[4.1.0]heptane (13, n = 2) and a 85% yield of pure c/5-9-methylenebicyclo[6.1.0]nonane (13, n = 6) were obtained from the 1-chloro-l-methylcyclopropanes 12 derived from cyclohexene and (Z)-cyclo-octene, respectively. ... 

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