Evidence for heterolytic cleavage of a cyclic oxonium ylide: implications for the mechanism of the Stevens [1,2]-shift

Formation and rearrangement of several oxonium ylides containing cyclopropylcarbinyl migrating groups were studied. Efficient ring-contraction by [1,2]-shift to form cyclopropane-substituted cyclobutanones was observed, with no competing cyclopropane fragmentation. Substitution with the hypersensiti...

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Bibliographic Details
Published in:Chemical communications (Cambridge, England) England), 2017-11, Vol.53 (94), p.12654-12656
Main Authors: Hosseini, Seyedeh Nargess, Johnston, Jeffrey R, West, F. G
Format: Article
Language:English
Subjects:
Cleavage
Cyclopropane
Fragmentation
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Summary:Formation and rearrangement of several oxonium ylides containing cyclopropylcarbinyl migrating groups were studied. Efficient ring-contraction by [1,2]-shift to form cyclopropane-substituted cyclobutanones was observed, with no competing cyclopropane fragmentation. Substitution with the hypersensitive mechanistic probe ( trans , trans -2-methoxy-3-phenylcyclopropyl)methyl led to cyclopropane fragmentation via an apparent heterolytic pathway, providing the first evidence for ion pair intermediates from ylide cleavage, and suggesting a possible alternative heterolytic mechanism for the Stevens [1,2]-shift. In contrast to prior evidence for a homolytic mechanism, a cyclopropylcarbinyl-substituted oxonium ylide furnished cleavage products consistent with a zwitterionic intermediate.
ISSN:1359-7345
1364-548X
DOI:10.1039/c7cc07716e