Department of Chemistry, Zhejiang University, 20 Yugu Road, Hangzhou 310027, People's Republic of China.
J Org Chem. 2012 Mar 16;77(6):2959-65. doi: 10.1021/jo202633c. Epub 2012 Feb 28.
A quinidine-derived squaramide Ib catalyzed cyclization reaction of β-oxo aldehydes 1 and aliphatic or aromatic β,γ-unsaturated α-keto ester 2 is described. Using cyclic aldehyde substrates, this procedure provided a promising approach to a variety of spiro-3,4-dihydropyrans bearing three continuous quaternary and tertiary stereocenters in moderate to good yield with high stereoselectivities. Substituents on the nitrogen atoms of the squaramide moiety of the catalyst proved crucial to the reaction outcome. The stereochemistry of the three newly formed chiral centers (trans-selective) of the major product indicates a Micheal addition/hemiacetalization domino sequence for the present annulations.
一种来源于奎尼丁的双酰胺 Ib 催化了β-氧代醛 1 和脂肪族或芳香族β,γ-不饱和α-酮酯 2 的环化反应。使用环状醛底物，该方法为各种螺-3,4-二氢吡喃提供了一种很有前途的方法，这些螺-3,4-二氢吡喃带有三个连续的季碳和叔碳立体中心，产率中等至良好，立体选择性高。催化剂中双酰胺部分的氮原子上的取代基对反应结果至关重要。主要产物中三个新形成的手性中心（反式选择性）的立体化学表明，目前的环化反应是迈克尔加成/半缩醛化的多米诺序列。
