Allylmethyl-Cyclopropylmethyl-Cyclobutyl Systems

Allylmethyl-Cyclopropylmethyl-Cyclobutyl Systems. A further note of caution has been sounded on the use of coupling constants as criteria for the presence, 

A ferrocenyl substituent attached to the carbonium ion centre of a cyclopropylmethyl cation provides stabilization of such a magnitude that homoallylic delocalization cannot be detected by spectroscopic methods, and quenching yields unrearranged products. Somewhat related is the observation of optically active bridgehead 

By studying the perchloric acid-catalysed acetolysis of the exo- and endo-[2- H]-alcohols (323), Friedrich and Cooper have established that cyclopropylcarbinyl rearrangement does occur in bicydo [n, 1,0]alkane systems. Electrophilic addition to the double bond of vinylcyclopropanes leads to products with retained (major) and rearranged (minor) skeletons. Reactions with bromine and chlorine as well as 

Tiffeneau-Demjanov ring enlargement of (333) to (334) has been recorded and cyclo-propylmethyl- cyclobutyl rearrangement is obviously involved/ 

Allylmethyl-Cyclopropylmethyl-Cyclobutyl Systems. The cyclopropylmethyl cation has been the subject of semi-empirical natural orbital analysis, and the bonding analysis supports the suggestion that there is delocalization of charge throughout the species. MINDO/3 geometries have been obtained for both planar and non-planar homotropylium cation, and the results of the study show the ion to be best represented as an open species and not as a delocalized bicyclo[5,l,0]octadienyl cation, as previously suggested.  

Berg-Nielsen and L. Skattebel, Acta Chem. Scand. (B), 1975,29,985. 

The solvolyses of 3,3-diphenyl- and 3,3-dimethylcyclobutyl tosylates are consistent with cyclobutyl-cyclopropylmethyl cation intervention, but definitive data are lacking. The benzylic cation derived from exo- or e io-(359) also derives stabiliza- 

The earlier proposal that vinylcyclopropane (365) was implicated in the solvolysis of (366) and (367) has now been substantiated, with all three compounds reacting from the common intermediate (368). A similar, though more complex, situation holds for the allenes (369)—(372).  

Rearrangements have also been observed in D-allo- and D-manno-pyranosides, in certain cyclo-octa-triene and -tetraene derivatives, and in the cleavage of the 1,3-photoadduct between cyclobutene and benzene.  

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Electrophilic ring opening of bicyclo[l. 1.0]butanes generally leads to mixtures of cyclobutyl, cyclopropylmethyl and allylmethyl compounds, among which the first two products dominate.The parent bicyclo[1.1.0]butane (1) is converted into cyclobutanol and cyclo-propanemethanol, without formation of any but-3-en-l-ol, upon treatment with 0.001 N sulfuric acid. Acetolysis of bicyclo[1.1.0]butane affords a mixture of all three acetates. In general, the product ratio is highly dependent on the substitution pattern of the bicyclic system. 

Cyclobutyl-Cyclopropylmethyl-Allylmethyl Systems. The long-accepted picture that interconversions amongst the cations in this system take place via a rapid equilibrium of classical structures has recently been criticized by Olah. He has argued, on the basis of n.m.r. evidence, in favour of non-classical a-delocalized structures for primary cyclopropylcarbinyl cations, although recognizing that localized, and even static, structures are involved in secondary and tertiary cases, and especially in the 8,9-dehydro-2-adamantyl series. Hehre and Hiberty have now questioned the (T-delocalized picture of the parent ion presented by Olah, and provide ab... 

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