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 crystalstructure analysis of 1 in combination with calculations on model compounds indicate the formation of a reactive
Cu II-(双)恶唑啉络合物1空气稳定且可回收,可有效催化β,γ-不饱和α-酮酸衍生物2和乙烯基醚之间的非对映和对映选择性杂Diels-Alder反应,用于合成取代的二氢吡喃3 [等式 (1)]。1的晶体结构分析结果与对模型化合物的计算相结合,表明通过用螯合底物取代两个H 2 O配体,形成了反应性中间体。X = OEt,N(OMe)Me;R =烷基,芳基,烷氧基,硫代苄基。
Cu(II) complexes of hydroxy oxazolines derived from (+)-(S)-ketopinic acidcatalyze the asymmetric hetero-Diels-Alder cycloaddition of enol ethers and β,γ-unsaturated α-keto esters. The reaction takes place with unprecedented exo selectivity providing 2,4-trans-disubstituted chiral 2,3-dihydropyrans with up to 88% ee.
Valuable substrates for the synthesis of natural products, compounds 3 (R1 =alkyl, aryl, alkoxy; R2 , R3 =alkyl) are formed from β,γ-unsaturated α-keto esters 1 and vinyl ethers 2 by the title reaction [Eq. (1)]. Copper(II) bisoxazolines act as catalysts, and in many cases enantiomeric excesses higher than 99.5 % are achieved.