Alcohols perruthenate

Ley et al. reported oxidation of alcohols catalyzed by an ammonium perruthenate catalyst dissolved in [NEtJBr and [EMIM][PFg] [60]. Oxygen or N-methylmorpholine N-oxide is used as the oxidant and the authors describe easy product recovery by solvent extraction and mention the possibility of reusing the ionic catalyst solution. 

For example, whereas the solid oxidation catalyst MCM-41-entrapped perruthenate can be used for the conversion of benzyl alcohols only, a similarly perruthenated-doped amorphous ORMOSIL is equally well suited for a variety of different alcohol substrates.35 On the other hand, a uniform pore structure ensures access to the active centres, while in an amorphous material made of non-regular porosity hindered or even blocked sites can well exist (Figure 1.16), rendering the choice of the polycondensation conditions of paramount importance. 

R. Ciriminna and M. Pagliaro, Tailoring the Catalytic Performance of Sol-Gel-Encapsulated Tetra-n-propylammonium Perruthenate (TPAP) in Aerobic Oxidation of Alcohols, Chem. Eur. J., 2003, 9, 5067. 

Catalytic oxidant.1 In combination with N-methylmorpholine N-oxide (7,244) as the stoichiometric oxidant, this ruthenium compound can be used as a catalytic oxidant for oxidation of alcohols to aldehydes or ketones in high yield in CH2C12 at 25°. Addition of 4A molecular sieves is generally beneficial. Racemization is not a problem in oxidation of alcohols with an adjacent chiral center. Tetrabutylammonium perruthenate can also be used as a catalytic oxidant, but the preparation is less convenient. 

The protocol for the oxidation of alcohols (10.6.20) has been improved by the use of molecular oxygen as the oxidant in the presence of a catalytic amount of the perruthenate catalyst (10.6.21). Yields are extremely high with relatively short... 

A molecular sieves (0.5 g) and polymer-supported perruthenate (0.1 g), prepared by adding KRu04 (10 mg, 1 mmol) to Amberlyst IR-27 resin (1 g), in CH2C12 or MeCN (5 ml) at room temperature until TLC analysis indicates complete consumption of the alcohol (ca. 16 h). The mixture is filtered and the filtrate evaporated to yield the carbonyl compound [e.g. PhCHO, >95% (16 h) PhCH=CHCHO, >95% CH2=CH(CH2)2CHO, 62% n-C7HI5CHO, 54% cyclohexanone, 50%]. The resin can be reused without loss of activity. 

The perruthenate oxidation of alcohols has been incorporated into a one-pot conversion of alkenes into carbonyl compounds via their initial hydroboration [44], Overall yields can be as high as 98%. Where the initial alkene also contains carbonyl groups these are reduced in the first step and are reoxidized by the perruthenate. 

Unambigous structural confirmation was obtained by converting 53a to diol carbonate 56, which was independently synthesised from baccatin III. Selective deprotection of 53a with TBAF gave alcohol 54, which was oxidised with tetra-n-propylammonium perruthenate/)V-methylmorpholine A -oxide (CH2CI2, molecular sieves, 25 °C, 1.5 h) to ketone 55 in 86% overall yield from 53a. Deprotection (HF, pyridine, CH3CN, 96%) of gave diol carbonate 56, identical to the compound prepared from baccatin III. 

Ley et al. performed oxidations of activated (benzyhc, allylic) alcohols by employing polymer-attached perruthenate catalysts and oxygen as oxidant. Triethylammo-... 

R. Lenz, S. V. Ley, Tetra-n-propyl ammonium perruthenate ( TPAP)-Catalyzed Oxidations of Alcohols using Molecular Oxygen as a Co-oxidant, J. Chem. Soc., Perkin Trans. 1, (1997) 3291-3292. 

D. L. Wu, A. P. Wight, M. E. Davis, Shape Selective Oxidation of Primary Alcohols using Perruthenate-Containing Zeolites, Chem. Commun. 6 (2003) 758-759. 

M. Hasan, M. Musawir, P. N. Davey, I. V. Kozhevnikov Oxidation Of Primary alcohols to aldehydes with Oxygen Catalyzed by Tetra-n-propyl ammonium perruthenate,, J. Mol. Catal. A Chem. 180 (2002) 77-84. 

R. Cirimiima, P. Hesemaim, J. J. E. Moreau, M. Carraro, S. Campestrini, M. Pagliaro, Aerobic Oxidation of Alcohols in Carbon Dioxide with Silica- Supported lonie Liquids Doped with Perruthenate, Chem. Eur. J. 12 ( 2006) 5220-5224. 

H. Hamamoto, M. Kudoh, H. Takahashi, H. Natsugari, S. Ikegami, Polyaerylamide-based Functional Polymer-Immobalized Perruthenate for Aerobic Alcohol Oxidation, Chem. Lett. 36 (2007) 632-633. 

Hydroboration occurred from the less hindered top face of rac-29 and resulted in the formation of alcohol rac-30. After a three-step sequence which included oxidation with tetrapropylammonium perruthenate (TPAP), methyl lithium addition and repeated oxidation with TPAP, ketone rac-31 was isolated. Finally, epimerization of the stereogenic center at C-7 to the correct configuration and methylenation with the Lombardo reagent led to the formation of racemic kelsoene (rac-1). 

Various solid-supported perruthenate reagents have been designed for the oxidation of alcohols.Solid-supported NMO has also been used. A number of perruthenate systems employing O2 as the terminal oxidant have also been reported. The use of ionic liquids based upon substituted imidazolium cations as alternative solvent media for the selective oxidation of alcohols to aldehydes and ketones has also been investigated. ... 

Polymer supported sodium ruthenate is able to catalyze the oxidation of alcohols with iodosobenzene or tetrabutylammonium periodate in CH2CI2.8 It is not clear whether the primary oxidant is ruthenate or perruthenate. 

In fact, equilibria between ruthenium ions in different oxidation states in aqueous solution add complexity to the mechanistic analysis of these oxidations. Thus, Burke and Healy presented mechanistic evidences9 suggesting that putative oxidations of alcohols with ruthenate ion are in fact produced by perruthenate originated by dismutation of ruthenate. 

Griffith, Ley et al.n discovered that, in variance with the instability and complex behaviour of perruthenate and ruthenate ions in aqueous solution, TPAP in organic media is quite stable and behaves as a very good oxidant for alcohols. Normally, it is employed in catalytic quantities in dry CH2CI2 with addition of TV-methylmorpholine /V-oxide (NMO) as the secondary oxidant. Catalytic TPAP in the presence of NMO is able to oxidize alcohols to adehydes and ketones under very mild conditions in substrates adorned by complex functionalities, and it has become one of the routine oxidants for alcohols in most Synthetic Organic Chemistry laboratories. 

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