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Intramolecular Reactions. Part 12. Ring Size and Leaving Group Effects on Inter- and Intra-molecular Nucleophilic Substitution by Carbanions

DOI: 10.1039/P29820000579

Source and publish data:

Journal of the Chemical Society. Perkin transactions II p. 579 - 584 (1982)

Update date:2022-08-05

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Authors:

Bird, RogerBird, Roger

Griffiths, GweryddGriffiths, Gwerydd

Griffiths, Gwynfor F.Griffiths, Gwynfor F.

Stirling, Charles J. M.Stirling, Charles J. M.

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Article abstract of DOI:10.1039/P29820000579

In cyclisations of aryl ο-halogenoalkyl ketones to aryl cycloalkyl ketones with base, cyclopropanes are formed up to 23000 times faster than cyclopentanes.Hydrogen-deuterium exchange experiments and very low bromide-chloride ratios (1.9) for three-membered ring formation are consistent with rate-determining deprotonation of the ketone.By contrast, in five-membered ring formation, hydrogen-deuterium exchange adjacent to the carbonyl group occurs much faster than cyclisation and the chloride-bromide ratio is 'normal' at 99.In formation of arylsulphonylcyclopropanes from arylsulphonylpropyl arenesulphonates, the Hammett ρ value for the leaving group is +1.7, and for intermolecular substitution by bis-sulphonyl stabilised carbanions, +1.2.Attempts to obtain ρLG values for five-membered ring formation were frustrated by competing intermolecular reactions.The results are discussed against the background of previous work on ring formation by intramolecular nucleophilic substitution.

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