Eco-Friendly Synthesis of Aminophenoxazinones from Aminophenols Catalyzed by Polyoxovanadate-Based MOFs Using Molecular Oxygen.

Achieving eco-friendly and efficient synthesis of aminophenoxazinones (APXOs) is of great research significance and practical value due to their widespread presence in pharmaceuticals, dyes, and natural products. Herein, we report two polyoxovanadate-based metal-organic frameworks with the general formula [M(Htmtib)2][V6O17] (M = Co 1, Ni 2; tmtib = 2,4,6-trimethyl-1,3,5-tri(imidazol-1-ylmethyl)benzene). As heterogeneous catalysts requiring no additives, both compounds are capable of catalyzing the oxidative condensation of o-aminophenol (OAP) to 2-aminophenoxazinone using molecular oxygen (O2) as an oxidant and in green ethanol (EtOH) medium, with yields of >99.0% (1) and 69.3% (2). Mechanistic studies reveal that the excellent performance of catalyst 1 stems from the synergistic action of its Co and V sites, which facilitate a radical pathway involving superoxide radicals. Furthermore, catalyst 1 not only exhibits satisfactory substrate tolerance but can also be recovered and reused for at least five cycles without compromising performance. More importantly, the catalyst also performed excellently in a gram-scale reaction (100 mmol, 10.9 g), delivering a 98.0% yield (49.0 mmol, 10.4 g) with a turnover number (TON) of 4900 and a low E-factor of 0.83, thus demonstrating the process to be both efficient and environmentally friendly. A polyoxovanadate-cobalt framework with dual-active sites catalyzes the additive-free oxidative condensation of o-aminophenols to aminophenoxazinones using molecular oxygen as an oxidant in a green ethanol medium, demonstrating excellent performance, recyclability, and feasibility for gram-scale reactions.