Synthesis and Solvolytic Reactivity of Unsaturated Cyclobutyl Bromides

Citation

Kiefer, Edgar Francis (1961) Synthesis and Solvolytic Reactivity of Unsaturated Cyclobutyl Bromides. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/KS0P-Y690. https://resolver.caltech.edu/CaltechETD:etd-04112006-152145

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. In order to study the effect of unsaturation electrons at the 3-position of a cyclobutyl carbonium ion, 3-methylenecyclo-butyl bromide and 1-methyl-l-bromocyclobut-2-ene have been synthesized and their rates of solvolysis in aqueous ethanol determined and correlated with the solvolytic rates of a series of analogous bromides. The synthesis of 3-methylenecyclobutanol, the precursor of 3-methylenecyclobutyl bromide, was accomplished by two independent schemes, both utilizing the cycloaddition reaction of allene and an activated olefin. Allene and vinyl benzoate afforded small yields of 3-methylenecyclobutyl benzoate, which liberated the alcohol on reduction. 3-Methylenecyclobutanecarbonitrile, obtained in good yield from allene and acrylonitrile by a published procedure, was converted to 3-methylenecyclobutylamine by hydrolysis followed by Curtius degradation. 3-Methylenecyclobutanol was obtained from the amine by nitrous acid deamination. 3-Methyl-3-bromocyclobutene was synthesized by dehydrobromination of 3-methyl-enecyclobutyl bromide, followed by low-temperature addition of one mole of hydrogen bromide. The rate of solvolysis of 3-methylenecyclobutyl bromide in aqueous ethanol was found to be appreciably slower than the value predicted from simple molecular orbital theory by assigning a small resonance integral between the 1- and 3-positions in the carbonium ion intermediate. It is concluded that "homoallylic resonance" is hindered in this system because the planar structure requires inefficient [...]-type overlap of the p-orbitals at the 1- and 3-positions, instead of the [...]-type orbital overlap which contributes to the startling rate enhancement observed elsewhere in the solvolysis of anti-7-norbornenyl derivatives, for example. Cross-ring interaction is considered to be of some importance in the methylcyclobutenyl carbonium ion, although the solvolysis rate data in this case permit a wide range of interpretation.

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