Catalytic aerobic oxidation of phenols to ortho-quinones with air-stable copper precatalysts

Abstract

A range of air-stable copper species was examined for catalytic activity in the catalytic aerobic transformation of phenols into ortho-quinones. Efficient catalysis was obtained with commercially available copper(II) acetate. The stability of all constituents before mixing makes for a practical process that advances previously reported copper(I)-based oxygenations.

A bio-inspired synthesis of oxindoles by catalytic aerobic dual C–H functionalization of phenols

“…S6 † ). These structural assignments are supported by previous work from us 24 , 25 and Stack, 22 ESI-MS characterization of the reaction mixture at short reaction times (Fig. S1–S2 † ), and the independent synthesis of SQ1–3 from Q1–3 , CuPF 6 and DBED ( Scheme 4 ).…”

“…11 b Inspired by the work of Stack 22 and others, 23 we developed conditions for the selective ortho -oxygenation of phenols that employ catalytic amounts of [Cu I (CH 3 CN) 4 ](PF 6 ) (abbreviated CuPF 6 ), N , N ′-di- tert -butylethylenediamine (DBED) and O 2 at room temperature. 19 , 24 , 25 Unlike the enzyme, however, which is selective for ortho -oxygenation, our conditions return coupled ortho -quinones that have undergone an additional C–H bond oxidation. This highlights important differences between the mechanism of our catalytic transformation and the mechanism of the enzyme, which we explore in the present work.…”

Tyrosinase and catechol oxidase activity of copper(I) complexes supported by imidazole-based ligands: structure–reactivity correlations

“…For a new ligand system, it is necessary to determine the active copper peroxide species. In the case of tyrosinase, the copper(I) ions are oxidized to copper(II) ions and bind dioxygen as peroxide in a characteristic side-on geometry (µ-η 2 :η 2 ) [12,22,65]. The intense absorption band between λ = 340-380 nm is due to an in-plane π σ * → d x 2 −y 2 charge transfer transition, and the less intense absorption feature between λ = 510-580 nm to an out-of-plane π v * → d x 2 −y 2 peroxo to copper(II) charge transfer transition [1,2,20].…”

“…This observation suggests the initial formation of 4-tertbutylquinone [58] and further reaction to the coupled ortho-quinone 4-(tert-butyl)-5-(3-(tert-butyl)phenoxy) cyclohexa-3,5-diene-1,2-dione [21,22] with a TON of 20 for CuL imz 1 and a TON of 6 for CuBIMZ (ε = 898 L mol −1 cm −1 at λ = 425 nm). The corresponding NMR spectra (Figs.…”

“…In 2013, Herres-Pawlis et al presented catalytic copper(I) model systems supported by bis(pyrazolyl)methane ligands which exhibit room temperature stable peroxo intermediates [20]. More recently, Lumb et al demonstrated catalytic conversions of different monophenols to a variety of organic products [21][22][23][24][25][26]. During the last years our group published a number of new copper(I) complexes functioning as model systems for tyrosinase [2,19,[27][28][29][30][31][32][33][34].…”