Regioselective and Stereoselective Pd-Catalyzed Intramolecular Arylation of Furans: Access to Spirooxindoles and 5H-Furo[2,3-c]quinolin-4-ones.

Herein, we report regio- and stereoselective intramolecular direct arylations of N-(2-bromophenyl)-2-furancarboxamides 1 to produce spirooxindoles 2 and 5H-furo[2,3-c]quinolin-4-ones 3 under different reaction conditions. Specifically, in the presence of Pd(PPh3)4 as a catalyst, PPh3 as a ligand, and K2CO3 as a base, substrates 1 underwent intramolecular α-arylation, possibly via a Heck insertion pathway, to provide 2, with the Z-isomer being favored. When the base was t-BuOLi and R1 was an aryl group, the reaction favored E-2, possibly via an electrophilic palladation pathway. In contrast, in the presence of PdCl2 as a catalyst, (o-OMePh)3P as a ligand, and PivOH as an additive, substrates 1 underwent intramolecular β-arylation to provide 3, possibly via a concerted metalation-deprotonation process.