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.