Ring protonated alkylcyclopropanes

Ring-protonated alkylcyclopropanes, well-known in solution , were suggested to explain the most unusual behaviour of heptyl ions. Extensive C- and D-labelling as well as a computer simulation and the analysis of CA data indicate that the major fragmentation reactions of CvHj s ions, generated via loss of I from 1-heptyl iodide, are preceded by extensive skeletal reorganization which via cyclopropane-like structures (140, 142, 144) eventually isomerize to tertiary carbocations (145 and 146, Scheme 23 where only the carbon skeleton is shown). The latter serve as actual precursors for the loss of CsH. ... 

The presence of a protonated cyclopropyl ring distinguishes the two norbomyl ions and one mi t hope to characterize a stabilized ion by its proton exchange behaviour. To do this one would have to investigate the exchange behaviour of protonated alkylcyclopropanes and tertiary and secondary cations in an acid sufficiently strong to stabilize all species for some time. 

Transient Three-membered Ring Compounds.—The existence of stable protonated alkylcyclopropanes as reactive intermediates has been discussed in detail. The collisional activation spectra of the gaseous ions formed upon protonation of pro-pene and cyclopropane are identical and the low activation energy for the conversion of protonated cyclopropane into the 2-propyl carbocation thus indicated is inconsistent with MINDO/3 calculations. Protonated cyclopropanes have been implicated in the reduction of (225) in the presence of strong acids and in the decomposition of cyclopropane on Zeolite HY. The involvement of the 3-methyl function in the deamination of 3-methyl-2-aminobutane has been evident for some time. However, studies with optically active and labelled substrates have now confirmed... 

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