Diastereoselective Synthesis of Dihydrobenzofuran Spirooxindoles and Their Transformation into Benzofuroquinolinones by Ring Expansion of Oxindole Core

A mild and efficient approach for the diastereoselective synthesis of dihydrobenzofuran spirooxindoles using 3-chlorooxindoles and imines is presented. This process involves a formal [4 + 1] annulation, yielding the product with excellent diastereoselectivity. Furthermore, a novel method for constructing benzofuroquinolinone scaffolds through the ring expansion of oxindoles has been established. This method involves a lactam ring expansion to the quinolinone skeleton. Besides, a one-pot procedure for creating benzofuroquinolinone scaffolds from 3-chlorooxindoles and imines is also provided.