An enantioselective synthesis of cis-dihydropyrans as the formal HDA reaction products was achieved through the catalyst-controlled anti-selective conjugate addition of aldehydes to β,γ-unsaturated α-keto esters. The observed unusual cis-selectivity could be attributed to the stabilization of the less favorable transition state for anti-conjugate adducts by the hydrogen bonding between the hydroxy group of the amino diol catalyst and β,γ-unsaturated α-keto esters.

中文翻译：

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二氢吡喃形成过程中催化剂控制的非对映选择性逆转†

通过醛控制的反选择性共轭醛加成到β，γ-不饱和α-酮酯中，可以实现顺式-二氢吡喃类化合物作为对映体HDA反应产物的对映选择性合成。观察到的异常的顺式选择性归因于氨基二醇催化剂的羟基与β，γ-不饱和α-酮酯之间的氢键，使抗共轭加合物的较不利的过渡态稳定。