Nickel(ii)-hydrazineylpyridine catalyzed regioselective synthesis of α-benzyl substituted β-hydroxy ketones via a Fenton free radical reaction

Abstract

Ni(II)-hydrazineylpyridine (Ni(II)-PyH)-catalyzed regioselective synthesis of α-benzyl substituted β-hydroxy ketones from α,β-unsaturated ketones and alcohols is reported via a Fenton free-radical reaction. This protocol enables facile access to desired products in good to excellent yields in 12 h using toluene solvent at room temperature to 100 °C. The structural analysis of the products was confirmed by ¹H, ¹³C-NMR, GC-MS, and HRMS data. Hydrogen peroxide used in the reaction facilitates Ni-catalyst oxidation state variations by a disproportionate reaction, which makes the catalyst recyclable up to 4 catalytic cycles without loss of activity. The method has high functional group tolerance with both aliphatic and aromatic ketones and alcohols. The catalyst structure was fully characterized using IR, UV, EPR and XPS analyses. The thermal stability of the catalyst was up to 290 °C, which was confirmed via a TGA study. The green metrics of the reaction showed 90%atom economy with a turnover frequency of 165.