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doi:10.1016/S0040-4039(00)61588-5 
Copyright © 1993 Published by Elsevier Science Ltd. All rights reserved.
Bis(imine)-copper(II) complexes as chiral lewis acid catalysts for the Diels-Alder reaction
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Received 14 July 1993;
Abstract
We report the Diels-Alder reactions of imide-derived dienophiles 2a–2d and 4b–4d with cyclopentadiene catalysed by square-planar Cu(OTf)2-bis(imine) complexes. The 2,6-dichlorophenyl-substituted ligand 1a was found to be generally the most effective for a range of substrates, affording products from 83–94% enantiomeric excess. Although endo:exo diastereoselectivity for the oxo-substituted imides 2a–2d is low, significant improvement is achieved with the thiazolidine-2-thione analogues 4b–4d, which provide enhanced dienophile reactivity and enhanced endo:exo diastereoselection.
Graphical Abstract
Diels-Alder reactions of the illustrated imides with the Cu(II) complexes of bis(imine) 1 are reported. With dienophiles 2a–2d, enantioselection is good (83–94% ee); however, the endo/exo selectivity is low. On the other hand, the sulfur analogues 4b–4d, exhibit excellent enantioselection (88–92% ee) and endo diastereoselection
