We began our experimental optimization with the coupling between benzaldehyde (1a) and N-Boc pyrrolidine (2a), where control experiments confirmed the necessity of catalyst, oxidant, and reductant (Table , entry 2). Ligand screening revealed that N-donor types together with Ni(II) pre-catalysts generally resulted in enhanced reactivities compared with NHC and phosphine ligands with Ni(COD)2, though further modification of the bis(pyrazole) pyridine (bpp) scaffold