Stereoselective Dynamic Cyclization of Allylic Azides: Synthesis of Tetralins, Chromanes, and Tetrahydroquinolines

This
report describes the stereoselective synthesis of 3-azido-tetralins,
-chromanes, and -tetrahydroquinolines via a tandem allylic azide rearrangement/Friedel–Crafts
alkylation. Exposure of allylic azides with a pendant trichloroacetimidate
to catalytic quantities of AgSbF6 proved optimal for this
transformation. This cascade successfully differentiates the equilibrating
azide isomers, providing products in excellent yield and selectivity
(>25 examples, up to 94% yield and >25:1 dr). In many cases,
the reactive
isomer is only a trace fraction of the equilibrium mixture, keenly
illustrating the dynamic nature of these systems. We demonstrate the
utility of this process via a synthesis of hasubanan.