TEMPO-oxidized

Treatment of D-glucose with nitromethane and sodium methoxide afforded nitrosugar 46 which, on reduction of the nitro group, protection of the resulting amine with Fmoc-Cl and TEMPO oxidation afforded 47 in a three-step sequence. 

Bean, cultivar Tempo Oxidant Benomyl (0.24% spray) Fungicide 32-41 303... 

Immobilized TEMPO has been used for the one-pot oxidation of alcohols to carboxylic acids as well.26 For this purpose TEMPO resin 1 was combined with two ion-exchange resins loaded with chlorite anions and hydrogen phosphate in the presence of catalytic amounts of potassium bromide and sodium hypochlorite in solution. The reaction required work-up for the removal of salts, but tolerated several protecting schemes and afforded pure products in good to excellent yields. The reaction is initiated by catalytic TEMPO oxidation of alcohols to aldehydes driven by dissolved hypochlorite followed by oxidation to the carboxylic acids effected by chlorite. 

Celluloses oxidized to an aldehyde at C6 are found for instance as intermediates of the TEMPO oxidation [50]. Depending on the reaction conditions a large number of such groups may survive in the final products, the poly-glucuronic acids, and also in partially TEMPO-oxidized pulps materials it is highly likely that a large number of carbonyl groups are present as C6-aldehyde. 

Fig. 17,16. Mechanism of the TEMPO oxidation of alcohols to aldehydes (TEMPO stands for tetramethylpiperidine nitroxyl).

Researchers at Tibotec patented a synthesis of racemic bis-THF alcohol ll.33 This synthesis used the multicomponent reaction developed by Ghosh and co-workers.34 As shown in Scheme 7, multicomponent reaction of dihydrofuran 12 and glyoxalate 28 provided 29 in 70-92% yield by GC. Reduction of 29 by NaBH4 gave 30 in 76% yield, which underwent an acid-catalyzed cyclization to give ( )-ll. This was subjected to a three-step process that included a TEMPO oxidation, NaBH4 reduction, and lipase resolution to provide optically active bis-THF (-)-ll. 

Tahiri, C. and Vignon, M. R., TEMPO-oxidation of cellulose Synthesis and characterisation of polyglucuro-nans. Cellulose 2000,1 (2), 177-188. 

Synthesis of the Repeating Unit of Streptococcus pneumoniae Type 3 through a Regioselective Tempo-Oxidation... 

The by-product could be avoided by choosing an alternative glycosyl donor, 61 [89], which, after coupling to 1,6-anhydro acceptor 45 and debenzylidenation, allowed the TEMPO-oxidation on a derivative with a protected 2,3-glycol... 

A novel one-pot Dess-Martin oxidation was developed for the construction of the y-hydroxy lactone moiety of the CP-molecules in the laboratory of K.C. Nicolaou. Bicyclic 1,4-diol was treated with 10 equivalents of DMP in dichloromethane for 16h to promote a tandem reaction first, the bridgehead secondary alcohol was selectively oxidized to the ketone, followed by a ring closure to afford the isolable hemiketal, which was further oxidized by DMP to give a keto aldehyde. Trace amounts of water terminated the cascade to give a stable diol, which was not further oxidized with DMP. Subsequent TEMPO oxidation furnished the desired y-hydroxy lactone. 

The following is typical—the aldehyde is used crude, and therefore the yield for the TEMPO oxidation is combined with the yield in the next step. 

In contrast to enzymatic or metal-catalyzed oxidation, the TEMPO-oxidation process is highly effective in the conversion of high molecular weight polysaccharides. Other advantages of this catalytic process are the high reaction rate and yield, the high selectivity, and little degradation of the polysaccharides [12]. 

Figure 7.18 Mechanisms of TEMPO oxidations. The top line shows the disproportionation of TEMPO in acid and the rest of the figure the acidic and basic mechanisms for oxidation of alcohols, with the reaction of hydrated aldehydes also indicated.

A multipolymer version of the aerobic TEMPO oxidation of alcohols in the presence of Cu(II) was also developed in the Toy group using immobilized TEMPO and polymer-supported 2,2 -bipyridine, which form the oxidative organometalhc complex with copper [31],... 

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