Exoselective 1,3-Dipolar [3 + 6] Cycloaddition of
Azomethine Ylides with 2‑Acylcycloheptatrienes: Stereoselectivity
and Mechanistic Insight
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Abstract
A highly <i>exo</i>-selective
1,3-dipolar [3 + 6] cycloaddition
of azomethine ylides with 2-acylcycloheptatrienes was realized with
a Cu(I)/(<i>S</i>,<i>R</i><sub>p</sub>)-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 <i>exo</i>-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
