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 <i>N</i>-(2-bromophenyl)-2-furancarboxamides <b>1</b> to produce spirooxindoles <b>2</b> and 5<i>H</i>-furo­[2,3-<i>c</i>]­quinolin-4-ones <b>3</b> 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 <b>1</b> underwent intramolecular α-arylation, possibly via a Heck insertion pathway, to provide <b>2</b>, with the <i>Z</i>-isomer being favored. When the base was <i>t</i>-BuOLi and R^<b>1</b> was an aryl group, the reaction favored <i>E</i>-<b>2</b>, possibly via an electrophilic palladation pathway. In contrast, in the presence of PdCl₂ as a catalyst, (<i>o</i>-OMePh)₃P as a ligand, and PivOH as an additive, substrates <b>1</b> underwent intramolecular β-arylation to provide <b>3</b>, possibly via a concerted metalation–deprotonation process