- Superiority of Very Weakly Basic Amines as Catalysts for Alpha-Proton Abstraction via Iminium Ion Formation
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Catalysis of the conversions of beta-ketol 6 and beta-acetoxy ketone 7 to enone 3 via amine-carbonyl condensation has been studied by using eight nontertiary amines having a pKa range from 10.61 to 1.22, including the very weakly basic 3,3,4,4-tetrafluoropyrrolidine (pKa = 4.05) and 1,1,1,3,3,3-hexafluoroisopropylamine (pKa = 1.22).Kinetic terms reflecting rate-determining alpha-proton abstraction via iminium ion formation were identified.Primary kinetic isotope effects were observed when appropriately deuterated 6 and 7 were used.Intermediate eniminium and enimmonium ions 17 were detected.Unlike general-base catalysis, catalysis via iminium ion formation becomes more effective as the base strength of the catalyst decreases.With 1 M hexafluoroisopropylamine as catalyst, formation of 3 from 7 occurs > 104 times via the iminium ion pathway for every time it occurs via direct general-base-catalyzed alpha-proton abstraction.
- Roberts, Rex D.,Ferran, Herbert E.,Gula, Michael J.,Spencer, Thomas A.
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- INVESTIGATION OF METHODS FOR THE SYNTHESIS OF AZIRIDINES AND AZIRINES ON THE BASIS OF ETHYL-β,β-BIS(TRIFLUOROMETHYL) ACRYLATE
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Various methods for the preparation of aziridines and azirines on the basis of ethyl β,β-bis(trifluoromethyl)acrylate were studied.Alkaline treatment of the products of addition of nucleophilic reagents to ethyl β,β-bis(trifluoromethyl)acrylate leads to t
- Eremeev, A. V.,Solodin, I. V.,Leipin'sh, E. E.,Kostyanovskii, R. G.
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p. 744 - 748
(2007/10/02)
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