Direct Synthesis of Dibenzotropones from o-Alkynylaryl Nitriles via Pd(II)-Catalyzed Cascade Reaction.

Abstract

Herein, we report a one-step Pd(II)-catalyzed strategy for the synthesis of synthetically challenging and medicinally important functionalized dibenzotropone scaffolds from readily accessible o-alkynylaryl nitriles and electron-rich aryl boronic acids. The cascade process involves regioselective 1,2-syn-carbopalladation, 1,4-palladium migration, unusual cis-trans isomerization of o-aryl-palladium species and intramolecular cyclization. Electronic tuning of aryl boronic acids enables the difficult cis-trans isomerization process. The protocol features good substrate scope with optimal functional group tolerance and is supported by control experiments and DFT studies elucidating the reaction mechanism and regioselectivity.