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On the Relative Preference of Enamine/Iminium Pathways in an Organocatalytic Michael Addition Reaction

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Title On the Relative Preference of Enamine/Iminium Pathways in an Organocatalytic Michael Addition Reaction
 
Creator PATIL, MP
SUNOJ, RB
 
Subject density-functional theory
polarizable continuum model
generalized gradient approximation
solvation free-energies
aldol reactions
ab-initio
carbonyl addition
enantioselective organocatalysis
alpha,beta-unsaturated aldehydes
asymmetric organocatalysis
ab initio calculations
density functional calculations
explicit solvents
michael addition
organocatalysis
 
Description The mechanism of the organocatalyzed Michael addition between propanal and methyl vinyl ketone is investigated using the density functional and ab intio methods. Different modes of substrate activation offered by a secondary amine (pyrrolidine) organocatalyst are reported. The electrophilic activation of enone (P-I) through the formation of an iminium ion, and nucleophilic activation of propanal (P-II) in the form of enamine have been examined by identifying the corresponding transition states. The kinetic preference for the formation of key intermediates is established in an effort to identify the competing pathways associated with the title reaction. A comparison of barriers associated with different pathways as well as intermediate formation allows us to provide a suitable mechanistic rationale for Michael addition reactions catalyzed by a secondary amine. The overall barriers for the C-C bond formation pathways involving enol or iminium intermediates are identified as hi-her than the enamine pathway. Additionally, the generation of iminium is found to be less favored as compared to enamine formation. The effect of co-catalyst/protic solvent on the energetics of the overall reaction is also studied using the cluster continuum approach. Significant reduction in the activation energies for each step of the reaction is predicted for the solvent-assisted models. The co-catalyst assisted addition of propanal-enamine to methyl vinyl ketone is identified as the most preferred pathway (P-IV) for the Michael addition reaction. The results are in concurrence with the available experimental reports on the rate acceleration by the use of a co-catalyst in this reaction.
 
Publisher WILEY-V C H VERLAG GMBH
 
Date 2011-09-01T19:13:45Z
2011-12-26T12:59:46Z
2011-12-27T05:52:36Z
2011-09-01T19:13:45Z
2011-12-26T12:59:46Z
2011-12-27T05:52:36Z
2009
 
Type Article
 
Identifier CHEMISTRY-AN ASIAN JOURNAL, 4(5), 714-724
1861-4728
http://dx.doi.org/10.1002/asia.200800351
http://dspace.library.iitb.ac.in/xmlui/handle/10054/12850
http://hdl.handle.net/10054/12850
 
Language en