An unprecedented synthetic approach
involving umpolung allylation/aza-Prins
cyclization of N-2,2,2-trifluoroethylisatin ketimines
is described. The reactions proceed smoothly with allyl bromide in
the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene, H2O,
and trimethylsilyl bromide; this one-pot protocol allows access to
six-membered spiro azacyclic oxindole derivatives in good to excellent
yields. Notably, while the general aza-Prins cyclization involves
amines and aldehydes, the present synthetic strategy represents the
first aza-Prins cyclization that utilizes the umpolung property of N-2,2,2-trifluoroethylisatin ketimines.
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