Heterogeneous Cobalt-Catalyzed Direct N-Formylation of Isoquinolines with CO2 and H2

Isoquinolines (IQs) are an abundant feedstock, and N-formyl-1,2,3,4-tetrahydroisoquinolines (FTHIQs) are valuable fine chemicals and key intermediates. Herein, we report for the first time the Co0/ZnCl2-catalyzed direct N-formylation of IQs by using CO2 with H2 to produce FTHIQs. It was discovered that the Co catalyst and ZnCl2 worked synergistically in catalyzing the N-formylation reactions, and moderate to high yields of the desired products could be obtained, depending on the nature of the substrates. The Co0 catalyst could be reused at least five times without a notable decrease in activity. A possible reaction mechanism is proposed on the basis of control experiments.