Selective copper(II)-catalyzed aerobic oxidative cleavage of aromatic gem-disubstituted alkenes to carbonyl compounds under neutral and mild conditions

Three copper(II) catalytic systems, CuC12.2H2O, CuC12 center dot 2H(2)0+phenanthroline, and [Cu(mu-Cl)Cl(phen)](2) were used to cleave alkenes to their corresponding carbonyl compounds under aerobic and neutral conditions. [Cu(mu-Cl)Cl(phen)](2) shows enhanced selectivity over the other two catalytic systems. The oxidative cleavage reactions were carried out in mixed H2O/THF solvent system under oxygen (4 atm) at 60 C. The real oxidant is 2-hydroperoxytetrahydrofuran, which is generated in situ in the process through the reaction between THF and oxygen catalyzed by copper(II). The cleavage reactions are selective for aromatic gem-disubstituted alkenes. Aromatic internal alkenes are slow to be oxidized, and both aliphatic terminal and internal alkenes are inert to oxidative cleavage. Free radical scavenger 2,2,6,6, tetramethylpiperidinyl-1-oxyl (TEMPO) deactivates the reaction indicating the involvement of free radical path in the reaction mechanism. (C) 2013 Elsevier Ltd. All rights reserved.