Metal-Catalyzed [6 + 3] Cycloaddition of Tropone with Azomethine Ylides: A Practical Access to Piperidine-Fused Bicyclic Heterocycles

The first metal-catalyzed [6 + 3]
cycloaddition of tropone with
azomethine ylides has been developed. With the use of a chiral ferrocenylphosphine–copper­(I)
complex as the catalyst, the asymmetric variant of the [6 + 3] cycloaddition
has also been successfully achieved. The reactions proceeded smoothly
under mild conditions, affording piperidine-fused bicyclic heterocycles
in moderate to high yields with good to excellent diastereo- and enantioselectivies.
The procedures are operationally simple and the catalysts are cheap
and readily accessible, thus providing a practical approach to piperidine-fused
bicyclic heterocycles.