22348-31-8Relevant articles and documents
Basicities and Nucleophilicities of Pyrrolidines and Imidazolidinones Used as Organocatalysts
An, Feng,Maji, Biplab,Min, Elizabeth,Ofial, Armin R.,Mayr, Herbert
supporting information, p. 1526 - 1547 (2020/02/04)
The Br?nsted basicities pKaH (i.e., pKa of the conjugate acids) of 32 pyrrolidines and imidazolidinones, commonly used in organocatalytic reactions, have been determined photometrically in acetonitrile solution using CH acids as indicators. Most investigated pyrrolidines have basicities in the range 16 aH aH aH 12.6) and the 2-imidazoliummethyl-substituted pyrrolidine A21 (pKaH 11.1) are outside the typical range for pyrrolidines with basicities comparable to those of imidazolidinones. Kinetics of the reactions of these 32 organocatalysts with benzhydrylium ions (Ar2CH+) and structurally related quinone methides, common reference electrophiles for quantifying nucleophilic reactivities, have been measured photometrically. Most reactions followed second-order kinetics, first order in amine and first order in electrophile. More complex kinetics were observed for the reactions of imidazolidinones and several pyrrolidines carrying bulky 2-substituents, due to reversibility of the initial attack of the amines at the electrophiles followed by rate-determining deprotonation of the intermediate ammonium ions. In the presence of 2,4,6-collidine or 2,6-di-tert-butyl-4-methyl-pyridine, the deprotonation of the initial adducts became faster, which allowed the rate of the attack of the amines at the electrophiles to be determined. The resulting second-order rate constants k2 followed the correlation log?k2(20 °C) = sN(N + E), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the two solvent-dependent parameters N and sN. In this way, the organocatalysts A1-A32 were integrated in our comprehensive nucleophilicity scale, which compares n-, -, and σ-nucleophiles. The nucleophilic reactivities of the title compounds correlate only poorly with their Br?nsted basicities.
Synthesis of enantiopure α-alkoxy-α-trifluoromethyl aldehydes and carboxylic acids from trifluoromethyl ketones
Fernandez, Rosario,Martin-Zamora, Eloisa,Pareja, Carmen,Vazquez, Juan,Diez, Elena,Monge, Angeles,Lassaletta
, p. 3428 - 3430 (2007/10/03)
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A short synthesis of (S)-2-(diphenylmethyl) pyrrolidine, a chiral solvating agent for NMR analysis
Bailey, David J.,O'Hagan, David,Tavasli, Mustafa
, p. 149 - 153 (2007/10/03)
A three step synthesis of (S)-2(diphenylmethyl)pyrrolidine 4 is described which allows its preparation on a large scale. The C2 symmetric diamines 5 and 6 have been prepared from 4 and are attractive as potential ligands for asymmetric transformations. Pyrrolidine 4 has been assessed as a chiral solvating agent for the NMR analysis of chiral compounds. It emerges as a good CSA for carboxylic acids and some secondary alcohols.
