Catalytic Asymmetric 1,3-Dipolar [3 + 6] Cycloaddition of Azomethine Ylides with 2‑Acyl Cycloheptatrienes: Efficient Construction of Bridged Heterocycles Bearing Piperidine Moiety

Conjugated cyclic
trienes without nonbenzenoid aromatic characteristic
were successfully employed as fine-tunable dipolarophiles in the Cu­(I)-catalyzed
asymmetric azomethine ylide-involved 1,3-dipolar [3 + 6] cycloaddition
for the first time, affording a variety of bridged heterocycles bearing
piperidine moiety in good yield with exclusive regioselectivity and
excellent stereoselectivity. 2-Acyl group is the key factor that determines
the annulation preferentially through [3 + 6]-pathway, while 2-ester
group modulates the annulation through [3 + 2]-pathway.