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Pd(II)-Catalyzed ortho-C–H Olefination/Dearomatization of N‑Aryl Ureas: An Approach to Imine Derivatives

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posted on 02.03.2016 by Pingping Jiang, Yongbao Xu, Fuxing Sun, Xufei Liu, Feng Li, Renfu Yu, Yang Li, Qifeng Wang
An unprecedented approach for the synthesis of imine derivatives was achieved via a Pd­(II)-catalyzed dearomatization reaction of N-aryl ureas with internal alkynes. The corresponding spirocyclic imine derivatives were obtained with 20 examples in good to excellent yields. Mechanistic investigation indicated that an interesting 1,3-palladium migration process led to the α-regioselective dearomatization when 2-naphthyl ureas were used as the substrates. Fused ring products could also be obtained to further prove this migration process.