Dimethyl-cyclo-propene

A diazo transfer reaction takes place, however, between diazoalkanes and derivatives of cyclopropene. Thus, in the reaction of dimethyl 3,3-dimethyl-cyclo-propene-l,2-dicarboxylate (2.200) with diazomethane, the primary product 2.201, a diaza bicyclo[3.1.0]hexene, isomerizes on irradiation to the diazo compound 2.202 (2-79). Acid catalysis, however, leads to the isomerization of 2.201 to the 1,4-dihydro-pyridazine 2.203 (Franck-Neumann and Buchecker, 1969). An analogous reaction of... 

In a large number of carbene and carbenoid addition reactions to alkenes the thermodynamically less favored jjyn-isomers are formed The finding that in the above cyclopropanation reaction the an/i-isomer is the only product strongly indicates that the intermediates are organonickel species rather than carbenes or carbenoids. Introduction of alkyl groups in the 3-position of the electron-deficient alkene hampers the codimerization and favors isomerization and/or cyclodimerization of the cyclo-propenes. Thus, with methyl crotylate and 3,3-diphenylcyclopropene only 16 % of the corresponding vinylcyclopropane derivative has been obtained. 2,2-Dimethyl acrylate does not react at all with 3,3-dimethylcyclopropene to afford rranj-chrysanthemic acid methyl ester. This is in accordance with chemical expectations since in most cases the tendency of alkenes to coordinate to Ni(0) decreases in the order un-, mono-< di- tri- < tetrasubstituted olefines. 

Disubstituted-a-bromocyclopropylcarboxamides eliminate HBr when treated with t-BuOK and 18-crown-6 ether in DMSO (dimethyl sulfoxide) at 40 °C, forming a cyclo-propene intermediate that adds an alcohol (nucleophile) at C(3) on the least hindered face of the cyclopropene ring. This is followed by an epimerization at C(l) forming (g) the most stable product, that is, a tra 5 -l,2,2,3-tetrasubstituted cyclopropane. The position of the nucleophile on C(3) is determined by the size of the groups on C(2) and the stereochemistry of the final addition product trans-) is determined by the epimerization at C(l). Two procedures are used for these reactions, with the best yields from the two methods ranging from 63 to 92% with diasteromeric ratios between 9 1 and 46 1 dr. 

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