Energy Barriers to Rotation in Axially Chiral Analogues of 4-(Dimethylamino)pyridine

The barriers to enantiomerization of a series of axially chiral biaryl analogues of 4-(dimethylamino)pyridine (DMAP) 1 − 10 were determined experimentally by means of dynamic HPLC measurements and racemization studies. The barriers to rotation in derivatives 1 − 6 (based on the bicyclic 5-azaindolin...

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Bibliographic Details
Published in:Journal of organic chemistry 2001-11, Vol.66 (22), p.7394-7401
Main Authors: Spivey, Alan C, Charbonneau, Patrick, Fekner, Tomasz, Hochmuth, Detlev H, Maddaford, Adrian, Malardier-Jugroot, Cecile, Redgrave, Alison J, Whitehead, Michael A
Format: Article
Language:English
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Summary:The barriers to enantiomerization of a series of axially chiral biaryl analogues of 4-(dimethylamino)pyridine (DMAP) 1 − 10 were determined experimentally by means of dynamic HPLC measurements and racemization studies. The barriers to rotation in derivatives 1 − 6 (based on the bicyclic 5-azaindoline core) were lower than those in the corresponding derivatives 7 − 10 (based on the monocyclic DMAP core). Semiempirical (PM3), ab initio Hartree−Fock (HF/STO-3G), and density functional theory (DFT/B3LYP/6-31G*) calculations reveal that these differences in barriers to rotation are the result of differing degrees of hybridization of the non-pyridyl nitrogen in the enantiomerization transition states (TSs). The importance of heteroatom hybridization as a factor in determining nonsteric contributions to barriers to rotation in azabiaryls of this type is discussed.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo015593q