The atropdiastereoselective torsion of a rapidly isomerizing axially prostereogenic biaryl unit, as present in the bridged naphthyl isoquinoline, (2R,4R)-3-benzyl-1,3,4,6-tetrahydro-8,9-dimethoxy-2,4-dimethyl-6-oxo-2H-naphtho [1′,2′: 4,5]pyrano[3,2-h]isoquinoline, (4) is described, by ring opening of the lactone function with simple achiral hydrogen nucleophiles. Profiting from an internal asymmetric induction, the reaction may be led to (1R,3R,7M) -2-benzyl-1,2,3,4-tetrahydro-7-(2-hydroxymethyl-4,5-dimethoxynaphth-1-yl)-1,3-dimethylisoquinolin-8-ol (5a), an intermediate in the stereocontrolled total synthesis of the liana alkaloid dioncophylline A (1a), or, optionally, to its atropdiastereomer 5b.
通过简单的不对映氢亲核试剂对内酯功能进行开环,可以得到快速异构化的轴向原位双芳基单元的旋光异构体选择性扭转,如桥联
萘基
异喹啉(2R,4R)-3-苄基-1,3,4,6-四氢-8,9-二甲氧基-2,4-二甲基-6-氧代-2H-
萘并[1′,2′:4,5]
吡喃并[3,2-h]
异喹啉(4)中所示。通过内部不对称诱导,该反应可以得到(1R,3R,7M)-2-苄基-1,2,3,4-四氢-7-(2-羟甲基-4,5-二甲氧基
萘-1-基)-
1,3-二甲基异喹啉-8-醇(5a),这是藤本植物
生物碱二氢
黄连素A(1a)的立体控制全合成中间体,或者可选择性地得到其旋光异构体5b。