1,3-Dipolar cycloaddition of α-alkoxycarbonylnitrones with vinyl ethers and allyl alcohols in the presence of Eu(fod)3:: selective activation of (Z)-isomers of the nitrones

Uncatalyzed cycloaddition of alpha-alkoxycarbonylnitrones 1 with vinyl ethers 7 gave mixtures of cis- and trans-cycloadducts 8, whereas Eu(fod)(3)-catalyzed cycloaddition of 1 with 7 gave the trans-cycloadducts trans-8 in a highly stereoselective manner. NMR studies indicated that Eu(fod)3 selectively activated (Z)-nitrones (Z)-1 in E,Z-equilibrium mixtures of nitrones 1. In contrast, the reaction of I with allyl alcohols 12 in the presence of Eu(fod)3 resulted in sequential transesterification and intramolecular cycloaddition to give intramolecular cycloadducts 13. (c) 2006 Elsevier Ltd. All rights reserved.