Trans-1,2-dimethyl-cyclopropane

Make molecular models of CIS- and trans-1,2-dimethyl-cyclopropane, and compare their strain energies. 

Electrophilic addition of bromine at — 60°C to cis- and trans-1,2-dimethyl-cyclopropanes has been shown to open the C-1—C-3 bond preferentially in a non-stereospecific manner. This rules out predominant reaction through a 1,3-bromonium ion. The principal difference between the cis- and transisomers is that the former gives 33 % of a 1,2-dibromide by 1,2-hydride shift within an intermediate carbonium ion. It has been reported that oxymercura-tion of optically active trans-1,2-dimethylcyclopropane occurs with at least 85 % inversion of configuration at the site of nucleophilic attack in a reaction which also cleaves the less substituted cyclopropane bond. Under the influ-... 

Fig. 1-11. Ball-and-stick models of cis and trans isomers of 1,2-dimethyl cyclopropane.

The stable products of the reaction are the cyclopropanes and isomeric olefins. The decomposition of cis- and tra j-3,5-dimethyl-1-pyrazolines are of special interest in that they exhibit a stereochemical reversal in the dimethyl cyclopropane product. The cw-pyrazoline forms predominantly trans, and the franj-pyrazoline predominantly cw-dimethyl cyclopropane. This is a consequence of the orbital symmetry of the intermediate trimethylene species which requires a conrotatory motion as the preferred mode of ring closure, and as such lends experimental support to the validity of Hoffman s mo calculations. 

Oxo-1,5-di-tert.-butyl - cyclohexadien - (1,4) - (3-spiro-l)-cis- 2,3 -dime -thyl-cyelopropan isomerisiert sich durch einen intramolekularen Energie-Transfer vom Dienon-System iiber einen Dreiring zum 6-Oxo-l,5-di-tert.-butyl-cyclohexadien-(l,4)-(3-spiro-l) - trans -2,3- dimethyl-cyclopropan 2 ... 

In their textbook, M. Diaz Pina and A. Roig Muntaner (Quimica Fisica, Vol. n, pp. 1073-1074, Editorial Alhambra, Madrid, 1976) reported the data below for the reversihle cis-trans isomerization of 1,2-dimethyl cyclopropane. Test these data to ascertain if they are consistent with a rate expression that is first-order in both the forward and reverse directions. 

Mishra and Crawford reported the synthesis of 3R,5R)- +)-trans-7>,5-dimethyl-1-pyrazoline 35 by different approach starting from alcohol 327 The pyrazoline 35 undergoes thermolysis, producing 25.6% of /ran -1,2-dimethyl-cyclopropane 36, processing 23% optical purity, and having the S S configuration. 

Permethrinic acid has two enantiomer pairs and four isomers (2" = 4) (Table B33, Appendix B). The acid leaving group for permethrin, cypermethrin, and cyfluthrin is permethrinic acid. The structure of this acid is given in Table 3. Angerer and Ritter (1997) separated the methyl esters of cis- and trans-permethrinic acid on a polysiloxane capillary column by GC (Table C18, Appendix C). The carboxylic acids of several of these pyrethroids were also listed as trans- or cw-3-(2, 2-dichlorovinyl)-2, 2-dimethyl cyclopropane carboxylic acid. The acids may be separated on a CHIREX phase 3005 column (Phenomenex, 2320 W 205th Street, Torrance, CA 90501) by HPLC. 

Phenoxyphenyl methyl (IR,S )-cis,trans-3-2,2 dichloropheny 1) 2,2-dimethyl cyclopropane carboxylate (approx. 60% trans 40% cis) Ambush Pounce ... 

Ethyl chrysanthemate (ethyl 2,2-dimethyl-3 c and t -[2-methylpropenyl]-cyclopropane carboxylate) [97-41-6] M 196.3, b 98-102 /llmm, 117-121 /20mm. Purified by vacuum distn. The free trans-acid has m 54° (from, EtOAc) and the free cis-acid has m 113-116° (from EtOAc). The 4-nitrophenyl ester has m 44-45° (from pet ether) [Campbell and Harper J Chem Soc 283 1945 IR Allen et al. JOrg Chem 21 29 1957]. 

NHase from Rhodococcus. sp. AJ270 was isolated, purified, and applied to the enantiose-lective transformation of a series of cyclopropane carbonitriles. Amides with moderate ee were isolated from conversion of many of the cyclopropane substrates, to yield the amides trans-( IR, 2/ )-3-phenylcyclopropane carbonitrile (49% conv. 22.7% ee), trans-( IS, 35)-2,2-dimethyl-3-phenylcyclopropanecarbonitrile (40% conv. 84.7% ee), trans-( IR, 3/f)-2,2-dibromo-3-phenylcy-clopropanecarbonitrile (11.6% conv. 83.8% ee), cis-( IR, 25)-3-phenylcyclopropanecarbonitrile (25.8% conv. 95.4% ee), and cis-(lR, 2S )-2,2-dimethyl-3-phenylcyclopropanecarbonitrile (7.9% conv. 3.2% ee) [43],... 

Thorough investigations with dimethyl diazomalonate and catalysts of the type (RO)3P CuX have revealed that the efficiency of competing reaction paths, the synjanti or EjZ selectivity in cyclopropane formation as well as the cis/trans ratio of carbene dimers depend not only on catalyst concentration and temperature but also on the nature of R58) and of the halide anion X 57 6". Furthermore, the cyclopropane yield can be augmented in many cases at the expense of carbene dimer... 

A striking example for the preferred formation of the thermodynamically less stable cyclopropane is furnished by the homoallylie halides 37, which are cyclopro-panated with high c/s-selectivity in the presence of copper chelate 3891 The cyclopropane can easily be converted into cw-permethric acid. In contrast, the direct synthesis of permethric esters by cyclopropanation of l,l-dichloro-4-methyl-l,3-pentadiene using the same catalyst produces the frans-permethric ester (trans-39) preferentially in a similar fashion, mainly trans-chrysanthemic ester (trans-40) was obtained when starting with 2,5-dimethyl-2,4-hexadiene 92). 

The change in selectivity is not credited to the catalyst alone In general, the bulkier the alkyl residue of the diazoacetate is, the more of the m-permethric acid ester results 77). Alternatively, cyclopropanation of 2,5-dimethyl-2,4-hexadiene instead of l,l-dichloro-4-methyl-l,3-pentadiene leads to a preference for the thermodynamically favored trans-chrysanthemic add ester for most eatalyst/alkyl diazoacetate combinations77 . The reasons for these discrepandes are not yet clear, the interplay between steric, electronic and lipophilic factors is considered to determine the stereochemical outcome of an individual reaction77 . This seems to be true also for the cyclopropanation of isoprene with different combinations of alkyl diazoacetates and rhodium catalysts77 . 

Lack of stereospecificity, extensive formation of olefinic products, and extensive tar formation limit the thermal decomposition of pyrazolines as a route to cyclopropanes.182 263 Light-induced decomposition of stereoisomeric pyrazolines establishes a method for the formation of cyclopropanes stereospecifically.222 Photolysis of 3-carbomethoxy-cis-3,4-dimethyl-l-pyrazoline (CCLI) produced cis-l,2-dimethylcycIopropane-l-carboxylate (CCLII) and without olefinic formation. Furthermore, irradiation of 3-carbomethoxy-trans-3,4-dimethyl-l-pyrazoline (CCLIII) gave [Pg.123]

Successive treatment of (-(-dimethyl succinate with LiTMP and bromochloromethane provides (S, S)-trans-cyclopropane-1,2-dicarboxylic ester in 99% de (equation 145)324. 

The determination that the cis and trans isomers of 1,2-d2-cyclopropane could be inter-converted thermally prompted experimental work on similar reactions exhibited by other substituted cyclopropanes to define activation parameters for representative instances of the isomerization and to begin to discriminate among alternative mechanistic suggestions. The 1,2-dimethyl- and 1-ethyl-2-methylcyclopropanes, for examples, were shown to approach cis, trans equilibrium with activation parameters log A, Ed (kcal mol"1) of 15.25, 59.4 and 15.08, 58.91 140. 

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