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Unraveling high precision stereocontrol in a triple cascade organocatalytic reaction

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Title Unraveling high precision stereocontrol in a triple cascade organocatalytic reaction
 
Creator SHINISHA, CB
SUNOJ, RB
 
Subject density-functional theory
asymmetric conjugate addition
diphenylprolinol silyl ether
tricyclic carbon frameworks
molecular-orbital methods
diels-alder reaction
gaussian-type basis
michael addition
domino reactions
alpha,beta-unsaturated aldehydes
 
Description The mechanism and stereoselectivity in an organocatalyzed triple cascade reaction between an aldehyde, electron deficient olefin and an alpha,beta-unsaturated aldehyde are investigated for the. first time using density functional theory. The factors responsible for high levels of observed stereoselectivity (Enders et al., Nature, 2006, 441, 861) towards the generation of cyclohexene carbaldehyde with four contiguous stereocentres are unravelled. The triple cascade reaction, comprising a Michael, Michael and aldol sequence as the key elementary reactions, is studied by identifying the corresponding transition states for the stereoselective C-C bond-formation. In the. first Michael addition step between the enamine (derived from the chiral catalyst and propanal) and nitrostyrene, energetically the most preferred mode of addition is found to be between the si-face of (E)-anti-enamine on the si-face of nitrostyrene. The addition of the si-face of the nitroalkane anion on the re-face of the iminium ion (formed between the enal and the catalyst) is the lowest energy pathway for the second Michael addition step. The high level of asymmetric induction is rationalized with the help of relative activation barriers associated with the competitive diastereomeric pathways. Interesting weak interactions, along with the steric effects offered by the bulky alpha-substituent on the pyrrolidine ring, are identified as critical to the stereoselectivity in this triple cascade reaction. The predicted stereoselectivities using computed energetics are found to be in perfect harmony with the experimental stereoselectivities.
 
Publisher ROYAL SOC CHEMISTRY
 
Date 2011-08-28T23:49:09Z
2011-12-26T12:58:15Z
2011-12-27T05:47:52Z
2011-08-28T23:49:09Z
2011-12-26T12:58:15Z
2011-12-27T05:47:52Z
2008
 
Type Article
 
Identifier ORGANIC & BIOMOLECULAR CHEMISTRY, 6(21), 3921-3929
1477-0520
http://dx.doi.org/10.1039/b810901j
http://dspace.library.iitb.ac.in/xmlui/handle/10054/11872
http://hdl.handle.net/10054/11872
 
Language en