Lewis Acid Catalyzed Cyclization of Glycals/2-Deoxy-d-ribose with Arylamines: Additional Findings on Product Structure and Reaction Diastereoselectivity

The cyclization reactions of arylamines with 2-deoxy-d-ribose or glycals were reinvestigated in the current report. In the montmorillonite KSF- or InCl3-initiated reactions of 2-deoxy-d-ribose with arylamines, a pair of diastereomeric tetrahydro-2H-pyran-fused tetrahydroquinolines was obtained in a nearly 1:1 ratio where the structure of one diastereomer was incorrectly assigned in the literature. Meanwhile, the diastereoselectivity in InBr3-catalyzed cyclization of glycals with arylamines was also incorrectly reported previously. It was found that high diastereomeric selectivity was achieved only when a C5-substituted glycal was used; otherwise, a pair of diastereomers was obtained in moderate yield with 1:1 diastereomeric ratio. Furthermore, tetrahydrofuran-fused tetrahydroquinolines 5b and 5b′ were also prepared successfully by using TBDPS-protected ribose as the glycal precursor and montmorillonite KSF as the activator.

本研究重新考察了芳胺与2-脱氧-d-核糖（2-deoxy-d-ribose）或糖烯（glycals）的环化反应。在蒙脱土KSF（montmorillonite KSF）或三氯化铟（InCl3）引发的2-脱氧-d-核糖与芳胺的反应中，得到了一对非对映异构的四氢-2H-吡喃并四氢喹啉类产物，其比例接近1:1，且其中一个非对映异构体的结构在既往文献中存在错误指派。与此同时，既往文献中关于三溴化铟（InBr3）催化糖烯与芳胺环化反应的非对映选择性结果也存在错误报道。研究发现，仅当使用C5位取代的糖烯时，才能获得较高的非对映选择性；否则仅能以中等收率得到比例为1:1的一对非对映异构体。此外，本研究还以叔丁基二苯基硅基（TBDPS）保护的核糖作为糖烯前体、蒙脱土KSF作为活化剂，成功制备了四氢呋喃并四氢喹啉类产物5b与5b′。