A Multicatalytic Domino Heteroannulation Approach to Dihydroquinolines

Significance

Reported is the synthesis of dihy­droquinolines 3 from propargyl amines 1 and arylboronic acids 2 using a mixed Rh/BINAP and Pd/X-Phos catalyst system. The reaction proceeds first via the Rh-catalyzed addition of the boronic acid to the alkyne to give 4, followed by a Pd-­catalyzed C-N coupling. Each of the two catalytic processes was optimized independently. Detailed control experiments showed that both phosphine ligands are required for efficient reaction since rhodium binds to BINAP and not X-Phos, while only Pd/X-Phos was capable of catalyzing the C-N coupling process. Interestingly, no unwanted Suzuki coupling products were observed under the optimized multicatalytic system, even when excess boronic acid was used. From further control experiments, it appears that the two catalytic cycles are independent of each other, with no direct interaction between the active metal complexes.