Tetrapropylammonium perruthenate, alcohols

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). 

The second example involves straightforward doping of methyl modified silica, denoted as ormosil, with tetrapropylammonium perruthenate via the sol-gel process [102] (Table 3). A serious disadvantage of this system are the low TOFs of 1.0 and 1.8 h 1 observed for a primary aliphatic alcohol and allylic alcohol, respectively. 

Fig. 14.14. TPAP oxidation of an alcohol to an aldehyde TPAP stands for tetrapropylammonium perruthenate.

There are problems associated with the expensive disposal of toxic waste from metal-based oxidations of alcohols. Thus, the focus has been largely on catalytic reactions as typified by Ley and Griffith s tetrapropylammonium perruthenate oxidant (section 7.1.6). Completely metal-free oxidations have much potential for environment-friendly oxidations, particularly if the reagent can be recovered and recycled. The most common metal-free oxidation of alcohols are TEMPO/oxone or TEMPO/N-chlorosuccinimide oxidation, Dess-Martin periodane oxidation (section 7.1.5) and Swern oxidation (section 7.1.4) and its several variants. 

Limitations of the reaction due to the substitution pattern of the allylic alcohols were overcome by the use of tetrapropylammonium perruthenate (TRAP) as a catalyst and monosubstituted, disubstituted and trisubstituted allyl alcohols were converted into the corresponding saturated aldehydes and ketones [5]. Intermediacy of the ruthenium alkoxide in this reaction was evidenced from the complete lack of reactivity of the trimethylsilyl ether derived from the allylic alcohol. 

The following Swern oxidation is an inexpensive, mild and fast transformation. It provides aldehydes starting from primary alcohols in the absence of water, exclusively. Other mild oxidation methods for the formation of aldehydes are known Dess-Martin periodinane (DMP), o-iodoxybenzoic acid (IBX), chromium(III) reagents, tetramethylpiperidine 7V-oxide and sodium hypochlorite (TEMPO/NaOCl), tetrapropylammonium perruthenate and N-methylmorpholine 7V-oxide (TPAP/NMO), " and palladium(II)-catalyzed oxidations are reported. ... 

Griffith, W. P., Ley, S. V., Whitcombe, G. P., White, A. D. Preparation and use of tetrabutylammonium perruthenate (TBAP reagent) and tetrapropylammonium perruthenate (TPAP reagent) as new catalytic oxidants for alcohols. J. Chem. Soc., Chem. Common. 1987,1625-1627. 

Hasan, M., Musawir, M., Davey, P. N., Kozhevnikov, I. V. Oxidation of primary alcohols to aldehydes with oxygen catalyzed by tetrapropylammonium perruthenate. J. Mol. Catal. A Chemical 2002, 180, 77-84. 

Practical Cr -catalyzed oxidations of alcohols have not been adopted widely, but Pr4N+ Ru04 (TPAP, tetrapropylammonium perruthenate) catalyzes the oxidation of alcohols to aldehydes by a stoichiometric oxidant such as NMO, H2O2, or O2 itself. The Ru(VII) complex oxidizes alcohols by the same mechanism described earlier for stoichiometric Cr species. The stoichiometric oxidant then reoxidizes the Ru(V) by-product back to Ru(VII). 

Tetrapropylammonium perruthenate Pr4N+Ru04 and N-methylmorpholine-N-oxide (NMO) as catalytic oxidants of primary, secondary, allylic and benzylic alcohols to carbonyl derivatives. The same catalyst polymer supported perruthenate (PSP) used as efficient oxidant (see 1st edition). 

F.i. Tetrapropylammonium Perruthenate-Ley Oxidation. Ruthenium derivatives have been used for oxidation reactions. A particularly useful one is TPAP, introduced by Ley for the oxidation of alcohols and called Ley oxidation. 1 2 a very mild oxidizing agent that is compatible with many sensitive... 

As a further extension, the Kim group very recently developed the aerobic oxidation and [l,5]-hydride transfer/cyclization sequence starting from readily available ortho tertiary amine substituted cinnamyl alcohols 24 (Scheme 4.12). The tetrapropylammonium perruthenate (TPAP) was identified as the competent catalyst for the initial aerobic oxidation of the allylic alcohols. The synthetically useful tetrahydroquinoline derivatives 25 were prepared in moderate yields and high level of enantioselectivity. 

Scheme 7.2 Oxidation of benzyl alcohol by tetrapropylammonium perruthenate.

The oxidation of alcohols with (l,l-dimethylethyl)benzene-sulfenamide is extremely mild and many sensitive functional groups such as epoxides and alkenes are tolerated hy the reaction conditions (eq 5). In the case of alcohol 1, oxidation with tetrapropylammonium perruthenate (TPAP) resulted in only 58% yield and Swern oxidation was unsuccessful. Epimerizable aldehydes such as the protected phenylglycinol 2 do not undergo racemization when oxidized (eq 6). ... 

Solandelactones A, B, E, and F have been synthesized by White et al., in which the diene side chain was installed using a Nozaki-Hiyama-Kishi reaction. Aldehydes 48 and 49 were prepared by tetrapropylammonium perruthenate oxidation of the corresponding alcohols and were immediately treated with CrCla and NiCl2 to afford the natural products solandelactone A, B, E, and F (Scheme 12.36). ... 

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