A higher energy conformer of (S)-proline is the active catalyst in intermolecular aldol reaction: Evidence from DFT calculations

被引:19
作者
Ajitha, Manjaly J. [1 ]
Suresh, Cherumuttathu H. [1 ]
机构
[1] CSIR, Natl Inst Interdisciplinary Sci & Technol, Computat Modeling & Simulat Sect, Trivandrum, Kerala, India
关键词
Organocatalysis; (S)-Proline; Aldol reaction; Proton transfer mechanism; Hydrogen bond catalysis; Dispersion-corrected DFT; DENSITY-FUNCTIONAL THEORY; ASYMMETRIC ALDOL; AMINO-ACID; NONCOVALENT INTERACTIONS; TRANSITION-STATES; PROLINE; ENAMINE; MECHANISM; STEREOSELECTIVITIES; ORGANOCATALYSIS;
D O I
10.1016/j.molcata.2011.05.016
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Full catalytic cycle of the stereoselective (S)-proline catalyzed aldol reaction of acetone and acetaldehyde in DMSO solvent has been investigated using three different DFT methods, viz. B3LYP, MPWB1K and B97D in conjunction with the polarizable continuum (PCM) method. At all the levels of theory, one of the higher energy conformers of the catalyst, 1b showed higher activity than the most stable conformer, 1a. On the basis of Delta G* of 39.8 kcal/mol observed for the reaction of 1a with acetone, 1a is considered to be inactive in the catalytic cycle while the same reaction with 1b showed 22.7 kcal/mol (B97D-PCM level) lower value for Delta G* than 1a. All the possibilities for enamine formation and C-C bond formation step have been considered for describing the most appropriate stereoselective catalytic cycle which showed that the full cycle is made up of a relay of eight proton transfer steps and the reaction is categorized under hydrogen bond catalysis. The hydration across the iminium bond of the second nucleophilic adduct - an intermediate formed subsequent to the aldehyde addition to the enamine - is the rate limiting step of the reaction with Delta G* = 21.7 kcal/mol (B97D-PCM level). (C) 2011 Elsevier B.V. All rights reserved.
引用
收藏
页码:37 / 43
页数:7
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