Dimethyl cyclopropanes, from decomposition

DIS(B)(42)1892]. Thermal decomposition in 2,3-dimethyl-2-butene gave a mixture of 144 and 145 [81DIS(B)(42)1892] (Scheme 39). Compound 145 might arise from attack of the carbene 139 (R = Ph) on the double bond of the 2,3-dimethyl-2-butene to give an intermediate cyclopropane... 

Two allyl cyclopropane-c s in equivalent amounts are actually observed to be formed. In the mercury sensitized decomposition of 5,5-dimethyl bicyclo [2.1.1] hexanone-2 (XXXI), the only cyclic hydrocarbons found are those derived from cyclopropane (38). 

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. 

Thermal decomposition of a tosylhydrazone salt has also been demonstrated as one of only few examples of methods for the generation of 1-substituted 1-vinylcyclopropanes from diazoalkenes. Heating the dilithiotosylhydrazone 26 in xylene in the presence of dimethyl fumarate generates the pentacyclic carbon skeleton 27 via two stereospecific cyclopropanations. ... 

Obtained from active methylene compounds, such as malonic esters, -0x0 esters and jS-oxo sulfones, iodonium ylides serve as precursors of the corresponding carbenes. Their decomposition by a catalytic amount of a copper salt in the presence of a C-C double bond has been used for inter- and intramolecular cyclopropanation reactions. Thus, reaction of cyclohexene with bis(methoxycarbonyl)methylene(phenyl)iodine(III) under the catalytic action of bis(acetylacetonato)copper(II) yielded dimethyl bicyclo[4.1.0]heptane-7,7-dicarboxylate (1) (38%, mp 91-93°C) in addition to tetrakis(methoxycarbonyl)ethene (41%). ... 

From Pyrazolines. —The decomposition of A -pyrazolines to cyclopropanes may be photochemically or thermally induced and the mechanisms of both processes are still under active investigation. Both trans- and cis-3,4-dimethyl-A -pyrazolines (90a) and (90b) give trans- and ds-l,2-dimethylcyclopropanes... 

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