Chiral C2 -Symmetric CuII Complexes as Catalysts for Enantioselective Hetero-Diels-Alder Reactions.

Air-stable and recyclable, the CuII -(bis)oxazoline complex 1 efficiently catalyzes diastereo- and enantioselective hetero-Diels-Alder reactions between β,γ-unsaturated α-keto acid derivatives 2 and vinyl ethers for the synthesis of substituted dihydropyrans 3 [Eq. (1)]. Results of the crystal structure analysis of 1 in combination with calculations on model compounds indicate the formation of a reactive intermediate through replacement of the two H2 O ligands with a chelating substrate. X=OEt, N(OMe)Me; R=alkyl, aryl, alkoxy, thiobenzyl. © 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.