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An AM1 theoretical study on the effect of Zn2+ Lewis acid catalysis on the mechanism of the cycloaddition between 3-phenyl-1-(2-pyridyl)-2-propen-1-one and cyclopentadiene
Author/Authors :
C.N Alves، نويسنده , , A.B.F. da Silva and A.L.M. Porto، نويسنده , , S Mart??، نويسنده , , V Moliner، نويسنده , , M Oliva، نويسنده , , J Andrés، نويسنده , , L.R Domingo، نويسنده ,
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هفته نامه با شماره پیاپی سال 2002
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Abstract :
The mechanism of the Diels–Alder reaction between 3-phenyl-1-(2-pyridyl)-2-propen-1-one and cyclopentadiene has been investigated with the AM1 semiempirical method. Stationary points for two reactive channels, endo-cis and exo-cis, have been characterized. The role of the Lewis acid catalyst has been modeled taking into account the formation of a complex between Zn2+ and the carbonyl oxygen atom and the pyridyl nitrogen atom of the 3-phenyl-1-(2-pyridyl)-2-propen-1-one system with and without the presence of two molecules of water around the cation. The mechanism of the uncatalyzed reaction corresponds to a concerted process, but in the presence of Lewis acid catalyst the mechanism changes and the reaction takes place through a stepwise mechanism. A first step involves the nucleophilic attack of the cyclopentadiene in the double bond of the dienophile which produces an intermediate. A second step involves the closure of the intermediate yielding the corresponding final cycloadduct. The inclusion of the Zn2+ catalyst drastically decreases the energy barrier associated with the carbon–carbon bond formation of the first step in comparison to the concerted process.
Keywords :
AM1 theoretical study , Diels–Alder reaction , Zn2+ Lewis acid catalyst
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