Enantioselective Aziridination Using Copper Complexes of Biaryl Schiff Bases

Racemic 2,2‘-diamino-6,6‘-dimethylbiphenyl is resolved using simulated moving bed chromatography, and the absolute configuration of the enantiomers is confirmed via the X-ray crystal structure of a derivative. The diamine is condensed with a range of aldehydes to give bidentate aldimine proligands L...

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Bibliographic Details
Published in:Journal of organic chemistry 2002-05, Vol.67 (10), p.3450-3458
Main Authors: Gillespie, Kevin M, Sanders, Christopher J, O'Shaughnessy, Paul, Westmoreland, Ian, Thickitt, Christopher P, Scott, Peter
Format: Article
Language:English
Subjects:
Catalysis
Catalysts: preparations and properties
Chemistry
Exact sciences and technology
General and physical chemistry
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
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Summary:Racemic 2,2‘-diamino-6,6‘-dimethylbiphenyl is resolved using simulated moving bed chromatography, and the absolute configuration of the enantiomers is confirmed via the X-ray crystal structure of a derivative. The diamine is condensed with a range of aldehydes to give bidentate aldimine proligands L. Molecular structures of the complexes formed between L and Cu(I) fall into two classes; bimetallic double helices ([Cu2L2]2+) and monometallic ([CuL]+). The latter are strikingly more efficient in the aziridination of alkenes than are the former in terms of rate, turnover, and enantioselection. In particular, the imine ligand formed from the diamine and 2,6-dichlorobenzaldehyde gives, in combination with Cu(I) or Cu(II), up to 99% ee in the aziridination of 6-acyl-2,2-dimethylchromene and 88−98% ee for a range of cinnamate esters. Styrenic and other alkenes are converted with lower selectivities (5−54%). The catalytic system shows a linear response in product ee to catalyst ee, and the product ee does not vary significantly during the reaction. UV spectrophotometric investigations indicate that conversion of Cu(I) to Cu(II) is not essential for catalysis but that Cu(II) is probably also a competent system.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo025515i