82777-32-0Relevant articles and documents
ELIMINATION AND ADDITION REACTIONS. PART 39. VARIATION OF NUCLEOFUGALITY WITH TRANSITION STATE STRUCTURE-1,3- AND 1,2-ELIMINATIONS FROM CARBANIONS COMPARED.
Issari, Bahram,Stirling, Charles J. M.
, p. 1043 - 1052 (2007/10/02)
Phenylsulphonyl-activated 1,3-eliminations have been investigated with the objective of determining nucleofugalities of six leaving groups.In cyclohexane-1,3-diyl and propane-1,3-diyl system unactivated 1,2-elimination of 'poor' leaving groups occurs faster than 1,3-elimination.In 2,2-dimethylpropane-1,3-diyl substrates, however, quantitative 1,3-eliminations occur and the nucleofugalities of Br, Cl, OTs, PhSO2, PhS, PhO, have been determined.In a linear free energy relationship extending over 15 pKa units and 12 rank units, an excellent correlation of nucleofugality with the pKa of the conjugate acid of the leaving group is found.It is concluded from the comparison with 1,2-eliminations previously studied that 1,3-elimination involves considerable leaving group separation and ring formation in the transition state.With bromide as leaving group, the 2,2-dimethylpropane-1,3-diyl system is 1000 times more reactive in cyclopropane formation than the propane-1,3-diyl system; this is the first quantitation of the Thorpe-Ingold effect in homocyclic ring formation.With chloride and tosylate leaving groups, smaller accelerations are observed.
Intramolecular Reactions. Part 12. Ring Size and Leaving Group Effects on Inter- and Intra-molecular Nucleophilic Substitution by Carbanions
Bird, Roger,Griffiths, Gwerydd,Griffiths, Gwynfor F.,Stirling, Charles J. M.
, p. 579 - 584 (2007/10/02)
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.
