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A DFT Study of the Molecular Mechanisms of the Diels−Alder Reaction between Cyclopentadiene and 3‐Phenyl‐1‐(2‐pyridyl)‐2‐propen‐1‐one − Role of the Zn 2+ Lewis Acid Catalyst and Water Solvent
Author(s) -
Domingo Luis R.,
Andrés Juan,
Alves Claudio N.
Publication year - 2002
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200208)2002:15<2557::aid-ejoc2557>3.0.co;2-8
Subject(s) - chemistry , cyclopentadiene , lewis acids and bases , lewis acid catalysis , diels–alder reaction , catalysis , reaction mechanism , concerted reaction , acid catalysis , nucleophile , computational chemistry , chiral lewis acid , medicinal chemistry , solvent effects , stereochemistry , solvent , organic chemistry
The molecular mechanism of the Diels−Alder reaction between cyclopentadiene ( 1 ) and 3‐phenyl‐1‐(2‐pyridyl)‐2‐propen‐1‐one ( 2 ) in the absence and in the presence of a Zn 2+ Lewis acid catalyst has been studied by quantum mechanical calculations at the B3LYP/6‐31G* level of theory. A continuum model was selected to represent the effects of the water as solvent. For the uncatalyzed process, two channels, endo and exo , were characterized, and the mechanism corresponded to an asynchronous concerted reaction associated with a [4+2] process. The presence of a Lewis acid catalyst changed the mechanism drastically, the reaction taking place by a polar stepwise mechanism. In the first step, a C−C sigma bond was formed by the nucleophilic attack of 1 on the conjugate position of the Lewis acid coordinated α,β‐unsaturated ketone to give a zwitterionic intermediate, while the second step was a ring‐closure process by this intermediate to give the final formally [4+2] cycloadduct. The theoretical results have been compared with available experimental data and an understanding of the role of Lewis acids and water solvent emerges from analysis of the results. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)