Synthesis of 1,5‐Diketones Using Benzyl Alcohols and Methyl Ketones Mediated by Phosphine Free Nickel(II) Complexes

In this research, we report two air stable, phosphine free nickel(II) based complexes, 1a and 1b comprised of the ligands, 2‐((mesitylimino)methyl)phenol ( HLA 1 ) and 2,4‐dibromo‐6‐((mesitylimino)methyl)phenol ( HLB 2 ). These complexes were employed as catalysts for the one‐pot coupling reaction of acetophenones with benzyl alcohols, to afford a series of substituted 1,5‐diketones. The desired diketones were produced in moderate to excellent isolated yield. The coupling reactions were carried out utilizing 5 mol% of the catalyst and 0.5 equivalents of t ‐BuOK at 115°C under aerial reaction conditions. The proposed mechanism for this coupling reaction was supported by 1 H NMR and mass spectral analyses of probable intermediates and various controlled experiments. These nickel complexes also demonstrated high catalytic efficacy in the coupling reaction of 2‐aminobenzyl alcohols with methyl ketones to produce quinolines with excellent yields.