Cyclopropylmethyl carbene

This type of cyclopropanation reaction catalyzed by a gold(I) complex produced cyclopropylmethyl carbene complex 321, which is reactive toward external alkenes or nucleophiles. The reaction depended on the ligand of the gold complex as well as the substituted patterns of enyne compounds. Echavarren and coworkers reported a cyclopropanation reaction mechanism. The cyclopropane gold complex intermediates 322 and 323 were trapped by external alkenes to give cyclopropanes 324 and 325, respectively (Scheme 1.157) [227]. 

The sodium salt of cyclopropanecarboxaldehyde tosylhydrazone (157) behaves similarly on heating to 125 135°C. Labelling experiments using the lithium cyclopropanecarboxaldehyde-p-tosylhydrazone salt has proved the occurrence of a cyclopropylcarbene-cyclobutene C3 - C4 ring expansion instead of a simple intramolecular carbene insertion in one of the four C-H bonds and bicyclobutane ring-opening . For other examples and discussion of such a rearrangement see Ref. 189. In an apparently related reaction, when cyclopropylmethyl tosylate (158) is treated with potassium t-butoxide in dimethyl sulphoxide at room temperature for 1 h, a quantitative mixture of cyclobutene and methylenecyclopropane is produced in equal amounts (equation 110) °. 

Similarly, the [cyclopropylmethyl(methyl)amino]carbene system reacted to give a cyclopropyl-methyl-substituted pyrrolinone. This cyclopropane-containing aminocarbene complex of chromium underwent alkyne insertion and formation of a heterocyclic ylide. Further rearrangements gave dihydro pyrrolones 17 and 18 with cyclopropylmethyl substituents. ... 

Dicyclopropylethylene has been used as a substrate to detect the triplet state in carbene cycloaddition. This depends on the fact that the rearrangement of the intermediate cyclopropylmethyl radical to the allyl-methyl radical is a very fast process. Thus in the addition of thermally generated fluorenylidene to cyclopropylethylene, (557) and (558) are among the products obtained. The ratio of (558) (557) is increased upon dilution, as expected for a carbene decaying to a triplet (biradical) ground state. 

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