Alcohols, reaction with perruthenate

An efficient and convenient methodology for the aerobic oxidation of alcohols catalysed by sol-gel trapped perruthenate and promoted by an encapsulated ionic liquid in supercritical carbon dioxide solution has been reported. The reaction is highly selective and useful for substrates otherwise difficult to oxidize.263 A four-component system consisting of acetamido-TEMPO-Cu(C104)2-TMDP-DABCO has been developed for aerobic alcohol oxidation at room temperature. The catalytic system shows excellent selectivity towards the oxidation of benzylic and allylic alcohols and is not deactivated by heteroatom-containing (S, N) compounds. The use of DMSO as the reaction medium allows the catalysts to be recycled and reused for three runs with no significant loss of catalytic activity.264... 

The oxidation of the alcohol was performed with supported perruthenate (8.48, Fig. 8.46) to produce clean aldehydes 8.91 after filtration. The Henry reaction was performed in the presence of a commercially available, supported strong base 8.92 and an excess of volatile nitroalkenes, giving clean nitroalcohols 8.93 after filtration and evaporation. The reaction mixtures from the trifluoroacetylation/elimina-tion steps were purified with commercially available amino PS resin 8.58 to scavenge the trifluoroacetates and with acidic ion-exchange resin 8.76 to remove the TEA-derived salts. Again, the nitrostyrenes 8.94 were obtained cleanly after filtration and evaporation. Cycloaddition with isocyanoacetate was promoted by the commercially available, supported guanidine base 8.95, while the subsequent N-alkylation of the pyrroles 8.96 was performed with an excess of halide in the presence of the commercially available, supported phosphazene 8.97. In this case, the excess halide was removed by treatment with supported 8.58, and filtra-... 

A catalytic method which promises to find wide application in view of its mildness and ease of execution uses a catalytic amount of tetra-n-propylammonium perruthenate (TPAP) with A7-methylmorpholine -oxide (NMO) as the cooxidant. ° l4imary (and secondary) alcohols which contain a range of ftinc-tional groups (alkenes, tetrahydropyran ethers, epoxides, lactones, silyl ethers and indoles inter alia) can be oxidized without interference by the other functional group (equations 21-23). The performance of the reagent is improved further by including molecular sieves in the reaction mixture. ... 

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. 

Tetra-A-propylammonium perruthenate (TRAP) has been known as a homogenous and versatile reagent for the catalytic oxidation of alcohols. One of the problems in the use of TRAP is its removal from the reaction ntixture. Ley et al. disclosed a system that permits recycling and reuse of TRAP [39]. They used TRAP and alcohol in CH Cl in the presence of l-ethyl-3-methyl-lH-imidazolium hexafluorophosphate ([emim][PFg]) and Et NBr accompanied with A-methylmorpholine A-oxide (NMO) as cooxidant. They demonstrated that both Et NBr and [anim][PF ] may be used to enable the recovery and reuse of TRAP. Also, performing the reaction under moderate oxygen pressure (30-40 bar) in dichloromethane and Et NBr at room temperature resulted in rapid and clean oxidation of sec-phenethyl alcohol. 

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... 

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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