Cyclopropylidenemethyl

The GIAO-MP2/TZP calculated 13C NMR chemical shifts of the cyclopropylidene substituted dienyl cation 27 show for almost all carbon positions larger deviations from the experimental shifts than the other cations 22-26. The GIAO-MP2/TZP method overestimates the influence of cr-delocalization of the positive charge into the cyclopropane subunit on the chemical shifts. Electron correlation corrections for cyclopropylidenemethyl cations such as 27 and 28 are too large to be adequately described by the GIAO-MP2 perturbation theory method and higher hierarchies of approximations such as coupled cluster models are required to rectify the problem. 

When cyclopropylidenemethyl(ethoxy)carbene chromium pentacarbonyl is treated with diphenylacetylene in THE, a mixture of products is obtained, from which only the tricarbonyl(5-ethoxy-6,7-diphenylbenzofuran)chromium complex could be isolated, in... 

Cyclopropylidenemethyl systems, in which one carbon of the double bond is already part of the cyclopropane ring, give especially stable vinyl cations owing to favorable geometry for overlap with participating cyclopropyl orbitals. This subject has also been reviewed recently in detaiP " and thus will only be summarized here briefly. 

The first report of the solvolysis of a cyclopropylidenemethyl derivative was in 1970 by Ghenciulescu and Hanack. This and other studies " have supported the involvement of a vinyl cation in the solvolyses of cyclopropylidenemethyl systems. 

Typical product-forming behavior for solvolyses of cyclopropylidenemethyl derivatives is that below. The l-bromo-2-methylcyclobutene results from ion-pair return. 

Of special interest for the present review is the study of the solvolysis of the a-cyclopropyl-substituted cyclopropylidenemethyl bromide This system, which... 

In the same way, the cyclopropylidenemethyl cations produced on solvolysis of cyclopropylidenemethyl bromides (103) undergo C3 - C4 ring enlargement into cyclobu-tanones depending upon the ability of the electron-releasing substituents in the a-position to stabilize the intermediate vinyl cations (equation 73). ... 

A particularly facile dimerization of a methylenecyclopropane was observed, when l-bromo-2-(cyclopropylidenemethyl)-3,4-dihydronaphthalene was treated with butyllithium in tetrahydro-furan at — 78 C, giving a mixture of 6 and dimer 7. ... 

Figure 6.15. Calculated and experimental C NMR spectra [109] for the 1-cyclopropyl-cyclopropylidenemethyl cation.

A silver(I)-catalyzed reaction of l-((cyclopropylidenemethyl)-2-alkynyl)-arene with 2-alkynylbenzaldoxime led to l-((l,3-dihydrobenzo[c]furan-l-yl) methyl)isoquinolines with a benzo[c]furan unit in good-to-excellent yields (14CC4188). 

The thermally induced intramolecular 2 + 2-cycloaddition of A(-(buta-2,3-dienyl)-2-cyclopropylidenemethyl)anilines (12) yielded functionalized bicyclo[4.2.0]nitrogen heterocycles (13) in high yield. DFT calculations indicate that the mechanism involves a concerted process in which a strained small ring is essential (Scheme 4). ... 

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