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

Abstract

Herein, we report regio- and stereoselective intramolecular direct arylations of N -(2-bromophenyl)-2-furancarboxamides 1 to produce spirooxindoles 2 and 5 H -furo[2,3- c ]quinolin-4-ones 3 under different reaction conditions. Specifically, in the presence of Pd(PPh 3 ) 4 as a catalyst, PPh 3 as a ligand, and K 2 CO 3 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 R 1 was an aryl group, the reaction favored E - 2, possibly via an electrophilic palladation pathway. In contrast, in the presence of PdCl 2 as a catalyst, ( o -OMePh) 3 P as a ligand, and PivOH as an additive, substrates 1 underwent intramolecular β-arylation to provide 3, possibly via a concerted metalation–deprotonation process.