Boron Tribromide-Assisted Chiral Phosphoric Acid Catalyst for a Highly Enantioselective Diels–Alder Reaction of 1,2-Dihydropyridines

BBr3–chiral phosphoric acid complexes are highly
effective and practical Lewis acid-assisted Brønsted acid (LBA)
catalysts for promoting the enantio­selective Diels–Alder
(DA) reaction of α-substituted acroleins and α-CF3 acrylate. In particular, the DA reaction of α-substituted
acroleins with 1,2-dihydro­pyridines gave the corresponding optically
active isoquinuclidines with high enantio­selectivities. Moreover,
transformations to the key intermediates of indole alkaloids, catharanthine
and allocatharanthine, are demonstrated.

三溴化硼（BBr₃）-手性磷酸复合物是一类高效且实用的路易斯酸辅助布朗斯特酸（Lewis acid-assisted Brønsted acid，LBA）催化剂，可用于催化α-取代丙烯醛与α-三氟甲基丙烯酸酯的对映选择性狄尔斯–阿尔德（Diels–Alder，DA）反应。
尤为值得关注的是，α-取代丙烯醛与1,2-二氢吡啶类化合物的DA反应可生成具有高对映选择性的光学活性异奎宁环类产物。
此外，本催化体系还可用于合成吲哚类生物碱的关键中间体卡特南碱（catharanthine）与别卡特南碱（allocatharanthine），相关转化过程已得到证实。