Cyclooctene, catalytic oxidation

In contrast to inactive iridium(TTI)-Peroxo complexes, Irm-hydroperoxo species have been shown to transfer oxygen to a coordinated alkene, for example in the slightly catalytic oxidation of cyclooctene to cyclooctanone by 02 + H2 mixtures in the presence of IrHCl2(CgH12) (equation 95). 68 Oxygen transfer presumably occurs as for palladium hydroperoxides in equations (89) and (90). 

This subject has recently been reviewed.647 Several additional papers have appeared on the catalytic oxidation of alkenes by 02 in the presence of PdCl(MeCN)2N02(148).64S Terminal alkenes and trans- cyclooctene yield the corresponding ketones, cyclopentene and cyclohexene the corresponding allyl alcohol, and bicyclic alkenes the corresponding epoxide. Heterometallacy-clopentanes such as (152) have been isolated from the reaction of (148) with norbornene (dicy-clopentadiene), and characterized by X-ray crystallography.6486 Glycol monoacetates were obtained from the reaction of (148) with terminal alkenes in acetic acid.649... 

The catalytic oxidation experiments were carried out in a round bottom flask equipped with condenser and stirrer. Typically, 6 or 12 mmol of substrate, 2 mmol bromobenzene (internal standard), 9 ml solvent (1,2-dichloroethane) and 100 mg zeolite (which contains typically around 2.9 pmol V (0.15wt%), TBHP/V ratio = 2070) were heated to 70°C, after which 6 mmol of TBHP in a 5.3 mmol chlorobenzene solution (which at the same time can function as an internal standard) were added to start the reaction. A sample was taken immediately afterwards. Before and during the reaction the mixture was purged with nitrogen for oxidations with cyclohexene and cyclooctene. Samples were filtrated over cotton wool and/or alumina, and triphenylphosphine was added to remove TBHP. In case of acetone as the solvent at 70°C, reactions were performed in a 50 ml autoclave and the reaction mixture was only purged with nitrogen before heating. After reaction TBHP was determined by iodometric titration. 

Gold-catalyzed oxidation of styrene was firstly reported by Choudhary and coworkers for Au NPs supported on metal oxides in the presence of an excess amount of radical initiator, t-butyl hydroperoxide (TBHP), to afford styrene oxide, while benzaldehyde and benzoic acid were formed in the presence of supports without Au NPs [199]. Subsequently, Hutchings and coworkers demonstrated the selective oxidation of cyclohexene over Au/C with a catalytic amount of TBHP to yield cyclohexene oxide with a selectivity of 50% and cyclohexenone (26%) as a by-product [2]. Product selectivity was significantly changed by solvents. Cyclohexene oxide was obtained as a major product with a selectivity of 50% in 1,2,3,5-tetramethylbenzene while cyclohexenone and cyclohexenol were formed with selectivities of 35 and 25%, respectively, in toluene. A promoting effect of Bi addition to Au was also reported for the epoxidation of cyclooctene under solvent-free conditions. 

Another non-heme system made use of hexadentate phenol ligands [98]. However, the catalytically active species was only formed upon ligand oxidation by excess of PhI=NTs. Furthermore, a large excess of the alkene was required (2000 equiv. vs. PhI=NTs). The reaction of cyclooctene and 1-hexene gave yields of about 50%, which represents a significant improvement over the earlier described copper systems [99]. 

Diederich et al. had postulated that the highly reactive iron-oxo species, arising from oxygen transfer from the oxidant to the Fem site [87], should be greatly stabilised by enclosure within a dendritic superstructure. The catalytic potential of the dendrimers 6 a-c was determined in the epoxidation of alkenes [83 a, 88] (1-octene and cyclooctene) and the oxidation of sulphides [83 a] ((methylsulphanyl)benzene and diphenyl sulphide) to sulphoxides - in dichloro-methane with iodosylbenzene as oxidising agent. Compared to the known metal-porphyrin catalysts, 6a-c exhibit only low TON (7 and 28, respectively, for... 

Asami and coworkers also investigated the deprotonation of cyclooctene oxide 97, which is known to undergo both a-deprotonation to yield transannular products and / -deprotonation to yield allylic alcohols 98 upon reaction with lithium amides. Using his catalytic system Asami and coworkers obtained the allylic alcohol in 27% yield and 54% ee of (,S )-98 (Scheme 68c). (Z)-4-Octene oxide 99 was deprotonated yielding the allylic alcohol 100 in 54% yield and 60% ee of the (5)-enantiomer (Scheme 68d)110. 

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