Regioselective Synthesis of 1,2-Dihydropyridines by Rhodium-Catalyzed Hydroboration of Pyridines

Pyridine undergoes addition of pinacolborane at 50 degrees C in the presence of a rhodium catalyst, giving N-boryl-1,2-dihydropyridine in a high yield. The selective 1,2-hydroboration also takes place in the reactions of substituted pyridines. In the reaction of 3-substituted pyridines, 3-substituted N-boryl-1,2-dihydropyridines are formed regioselectively.