Orbital-controlled stereoselections in sterically unbiased cyclic systems
Article Abstract:
Biased reactions in nucleophilic additions, electrophilic additions, and Diels-Alder cycloadditions are the results of the unsymmetrical pi face of the carbonyl and olefin groups arising from nonequivalent substituents. The unsymmetrical pi face of the carbonyl and the olefin groups involves unsymmetrization of pi orbitals. Studies on the pi facial selectivities of sterically unbiased cyclic systems of ketones, olefins, Diels-Alder dienophiles and Diels-Alder dienes reveal the presence of unpredictable steric effects due to conformational ambiguity.
Publication Name: Chemical Reviews
Subject: Chemistry
ISSN: 0009-2665
Year: 1999
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The exterior frontier orbital extension model
Article Abstract:
Investigations have been conducted on the major transition state models of pi-facial stereoselectivity of carbonyl reactions. A theoretical model, namely, the exterior frontal orbital extension model, has been formulated using the Salem-Klopman equation. This model assumes the importance of the ground state conformational and electronic properties of unsaturated substrates. The pi-facial difference in the magnitude of the reaction driving force is regarded as the origin of pi-facial stereoselection in nucleophilic carbonyl additions.
Publication Name: Chemical Reviews
Subject: Chemistry
ISSN: 0009-2665
Year: 1999
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Nucleophilic additions to 4,4-disubstituted 2,5-cyclohexadienones: can dipole effects control facial selectivity?
Article Abstract:
Investigations of the stereofacial selectivity of 1,2-nucleophilic attack to 4,4-disubstituted cyclohexadienones provide strong experimental evidence for dominant dipolar control in carbonyl addition reactions. Hyperconjugative orbital stabilization in the Felkin-Anh and the Cieplak sense or orbital distortion effects appear to be of secondary importance. A quantitative correlation of the calculated dipole moments of dienones with the facial selectivity is possible in analogy to Hammett linear free energy relationships.
Publication Name: Chemical Reviews
Subject: Chemistry
ISSN: 0009-2665
Year: 1999
User Contributions:
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