Selective aerobic oxidation of hydroxy compounds catalyzed by photoactivated ruthenium‐salen complexes (selective catalytic aerobic oxidation)

Abstract

Selective oxidation of alcohols to the corresponding carbonyl compounds is one of the most fundamental reactions in organic synthesis. Traditional methods for this transformation generally rely on stoichiometric amount of oxidants represented by Cr(VI) or DMSO reagents, though their synthetic utility is encumbered by unpleasant waste materials. From ecological and atom-economic viewpoints, catalytic aerobic oxidation is much more advantageous because molecular oxygen is ubiquitous and the byproduct is basically non-toxic water or hydrogen peroxide. On the other hand, phenol derivatives undergo oxidative coupling, forming C-C or C-O bond, through radical intermediates coupled with an electron-transfer process. Molecular oxygen is also well known to serve as electron acceptor in this reaction. Thus, a variety of transition metal complexes have so far been examined for aerobic oxidations of alcohols and phenols, and high catalytic activities have been achieved in some cases. However, stereo- and chemo-selective aerobic oxidations are still limited in number and are of current interest. Presented in this paper is our recent studies on catalytic aerobic oxidations with photoactivated nitrosyl ruthenium-salen complexes, including asymmetric oxidation of secondary alcohols to ketones (kinetic resolution), enantioselective oxidative coupling of 2-naphthols to binaphthols and oxygen-radical bicyclization of 2,2'-dihydroxystilbene, chemoselective oxidation of primary alcohols to aldehydes and diols to lactols, and asymmetric desymmetrization of meso-diols to lactols.

Environment Friendly Protocol for Enantioselective Epoxidation of Non-Functionalized Alkenes Catalyzed by Recyclable Homochiral Dimeric Mn(III) Salen Complexes with Hydrogen Peroxide and UHP Adduct as Oxidants

“…The catalytic activity (TOF) of complexes 1 and 2 was reasonably good for styrene (entries 1,2,13,14), 2,2-dimethylchromene (entries 7,8,19,20), 6-methoxy-2,2-dimethylchromene (entries 9,10,21,22) and 6-cyano-2,2-dimethylchromene (entries 11,12,23,24) with both the oxidants while indene showed good efficiency only with UHP (entries 15,16). However, the epoxidation reaction was slower with substrate spiro [cyclohexane-1,2¢-[2H] [1] chromene] (entries 5,6,17,18) with both the oxidants (figure 2).…”

“…Clearly, molecular oxygen is the most ideal oxidant for a number of oxidation reactions [3]. However, mostly only one oxygen atom of an oxygen molecule is used productively for epoxidation (50% atom efficiency) [4][5][6][7][8][9][10], thus at least stoichiometric amounts of unwanted by-products are generated during the reactions. Apart from molecular oxygen, hydrogen peroxide is highly attractive oxidant because of its low cost, high oxygen contents and environment friendly nature as water is the sole by-product [11,12].…”

Aerobic Oxidations in Asymmetric Synthesis: Catalytic Strategies and Recent Developments

“…Therefore, the most prominent examples have been judiciously selected among the research works published in the last 20 years. However, for a more detailed overview of the field, especially earlier contributions, a number of comprehensive reviews (Uchida and Katsuki, 2013;Bryliakov, 2015;Bryliakov, 2017;Ottenbacher et al, 2018), and personal accounts (Mukaiyama and Yamada, 1995;Irie and Katsuki, 2004) can be recommended for further reading.…”

Synthesis, structural characterization, and catalytic activity of ruthenium(II) monocarbonyl complexes with bidentate Schiff base and triphenylphosphine ligands

“…Ruthenium complexes containing tri-and tetradentate Schiff bases have been well studied [6][7][8][9], whereas, those with bidentate Schiff base ligands have received comparatively less attention [10]. There has been an increasing interest during recent years in ruthenium complexes with bidentate ligands containing π-acceptor and σ-donor groups [10,12].…”