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

Abstract

Three copper(II) catalytic systems, CuCl2·2H2O, CuCl2·2H2O+phenanthroline, and [Cu(μ-Cl)Cl(phen)]2 were used to cleave alkenes to their corresponding carbonyl compounds under aerobic and neutral conditions. [Cu(μ-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.