Synthesis of Six-Membered Spiro Azacyclic Oxindole Derivatives via a One-Pot Process of Umpolung Allylation/Aza-Prins Cyclization

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.