Exoselective 1,3-Dipolar [3 + 6] Cycloaddition of Azomethine Ylides with 2‑Acylcycloheptatrienes: Stereoselectivity and Mechanistic Insight

A highly exo-selective
1,3-dipolar [3 + 6] cycloaddition
of azomethine ylides with 2-acylcycloheptatrienes was realized with
a Cu­(I)/(S,Rp)-PPF-NHMe
complex as the catalyst, leading to a diverse range of bridged piperidines
with multiple functionalities in good yield with excellent stereoselectivity
control. Theoretical calculations indicated a stepwise mechanism for
this exo-selective [3 + 6] annulation, which accounts
for the remarkable feature of this annulation: all of the larger substituent
groups occupy the axial positions in the six-membered chairlike conformation
of the piperidine ring.