Cobalt-Catalyzed Selective Dearomatization of Pyridines to N–H 1,4-Dihydropyridines

Catalytic reduction of pyridines to N–H 1,4-dihydropyridines is exceptionally challenging because they are essential intermediates to form tetrahydropyridines. Using a facile dihydrogen source H3N·BH3 to activate the pyridine ring in situ, we have achieved selective transfer hydrogenation of nicotinate derivatives to N–H 1,4-dihydropyridines by cobalt-amido cooperative catalysis. The reactions operate smoothly under mild conditions to produce a variety of N–H 1,4-dihydropyridines with high chemo- and regioselectivity. This catalytic method also provides a practical protocol to regenerate Hantzsch analogues after delivery of H2.