Sustainable Synthesis of Pyrimidines by [NNO]-Pincer-Supported Nickel(II) Complexes via Dehydrogenative Annulation of Alcohols.

Abstract

An efficient strategy for the multicomponent synthesis of pyrimidine analogues has been demonstrated via acceptorless dehydrogenative annulation (ADA) of alcohols utilizing new Ni(II)-NNO pincer complexes as catalysts. The newly formed Ni(II) complexes (C1-C4) featuring N^N^O chelating hydrazone ligands are well established through analytical and spectral methods (FT-IR and NMR). Single-crystal X-ray diffraction analysis precisely reveals the NNO coordination fashion and square planar geometry around the metal center. The catalytic performance of the complexes is validated through the smooth and efficient synthesis of pyrimidine derivatives from the dehydrogenative coupling of primary alcohols, benzamidines/guanidines/acetamidines, and 1-phenylethanol and delivers the desired products up to 92% with a catalyst loading of 2 mol %. Time-dependent control experiments evidence the formation of probable intermediates such as aldehyde, ketone, and chalcone. The catalytic system displaces a variety of 2,4,6-trisubstituted pyrimidines (27 examples) and H₂O and H₂ are the sole byproducts. Additionally, a successful gram-scale synthesis highlights the industrial applicability of this catalytic protocol.