2,2,6,6 tetramethylpiperidine-1 -oxyl

The second synthesis of crystalline 43 was reported by Mori as summarized in Scheme 62 [93]. The building block (4.R,5S)-A was prepared by an enzymatic process, while another building block C was synthesized via Sharpless asymmetric epoxidation. Coupling of A with C gave D, which was cyclized under Op-polzer s conditions to give crystalline E. When E was oxidized with Dess-Martin periodinane or tetra(n-propyl)ammonium perruthenate or Jones chromic acid, crystalline 43 was obtained. Swern oxidation or oxidation with 2,2,6,6-tetramethylpiperidin-1 -oxyl of E afforded only oily materials. Accordingly, oxidation of E to 43 must be executed extremely carefully. A synthesis of oily 43 was reported by Gil [94]. 

A double mediatory system consisting of A-oxoammonium salts and active bromine species, generated from 2,2,6,6-tetramethylpiperidine-1 -oxyl derivatives... 

A convenient procedure for the oxidation of primary and secondary alcohols was reported by Anelli and co-workers (8,9). The oxidation was carried out in CH2CI2 with an aqueous buffer at pH 8.5-9.5 utilizing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 1) as the catalyst and KBr as a co-catalyst. The terminal oxidant in this system was NaOCl. The major disadvantage of using sodium hypochlorite or any other hypohalite as a stoichiometric oxidant is that for each mole of alcohol oxidized during the reaction one mole of halogenated salt is formed. Furthermore,... 

Tetramethylpiperidin-1-oxyl from Nacalai Tesque, Inc., Kyoto, Japan, also available from Janssen Chimica, Beerse, Belgium, was used. 4-Methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl, prepared according to the procedure of Endo,3 can also be used.4... 

Washing with hydrochloric acid and potassium iodide removes 2,2,6,6-tetramethylpiperidin-1-oxyl from the organic phase.6 Because of its volatility, the catalyst cannot be eliminated in the distillation of crude aldehyde. 

Tetramethylpiperidln-1 -oxyl 1 -Piperidinyloxy, 2,2,6,6-tetramethyl- (9) (2564-83-2) 4-Methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl 1-Piperidinyloxy, 4-methoxy-2,2,6,6-tetramethyl (11) (95407-69-5)... 

Tetramethylpiperidin-1-oxyl radical (TEMPO) immobilized on aminopropyl-modified silica gel... 

TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl TBACI = tetrabutyl ammonium chloride NCS = A/-chlorosuccinimide... 

Oxidation of the primary alcoholic group to a carboxyl group in diols with primary and secondary hydroxyls is accomplished by silver carbonate [377]. Unfortunately, an extremely large excess of the reagent is needed. Similar results are obtained with a rather exotic oxidant, 4-methoxy-2,2,6,6-tetramethyl-l-oxopiperidinium chloride, which is prepared by treatment with chlorine of a stable radical, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl. The compound oxidizes 1,4-butanediol to y-butyrolactone in 100% yield (isolated yield 81%) and 1,5-pentanediol to 8-valerolactone in 61% yield (isolated yield 40%) [995] (equation 292). 

Vicinal tricarbonyl compounds have been obtained from 2,3-dihydroxy-alkanoic esters with NaBr02 in combination with 4-benzoyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl. In an alternative method bromide ion is used to mediate electrooxidation. Epoxidation of alkenes. This reaction proceeds at room temperature in the... 

The stable, commercially available nitroxyl radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) 51 is an excellent catalyst, in conjunction with a co-oxidant, for the oxidation of alcohols. The most popular co-oxidant is buffered sodium hypochlorite (NaOCl). Oxidation of the nitroxyl radical gives the oxoammonium ion 52, which acts as the oxidant for the alcohol to form the carbonyl product. Primary alcohols are oxidized faster than secondary and it is often possible to obtain high chemoselectivity for the former. For example, oxidation of the triol 53 gave the aldehyde 54, with no oxidation of the secondary alcohols (6.44). The use of TEMPO is particularly convenient for the oxidation of primary alcohols in carbohydrates, avoiding the need for protection of the secondary alcohols. 

At this juncture, the stereochemistry of the amine-substituted carbon required inversion to the correct configuration of the natural product. Toward this end, lactone 354 was treated with tetramethylguanidine and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) under an air atmosphere in THE. These conditions led to oxidation to yield enamine 355, which was subsequendy reduced with sodium cyanoborohydride to complete the epimerization process. These conditions were also sufficiently hydridic to reduce the ketone carbonyl. Heating in ethyl acetate then led to cycHza-tion to yield lactam 356. Oxidation using IBX next provided ketone 357, which was employed as a coupling partner for 2-iodoanihne in the key indolization step (Scheme 51). 

One of the limitations of anionic polymerization with respect to preparation of block copolymers is the rather limited range of monomers that can be polymerized anionically to form polymers with well-defined stmctures. One solution to this problem is to utilize anionic polymerization to form a well-defined polymer that is functionalized with an end group that can be used to initiate polymerization via another polymerization method, for example, controlled free-radical polymerization. One such functional group is the aminoxy group which can be used to initiate nitroxide-mediated radical polymerization (NMP). °° PSLi has been reacted with 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl (MTEMPO), a stable nitroxide free radical, in THF at -78 °C as shown in eqn [30]. The mechanism of this functionalization was presumed to occur... 

The spin probe method was one of the first methods used to evaluate the free volume in polymers [1,7]. It is based on the principle that the rotational frequency of spin probes, usually stable nitroxyl radicals such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) is sensitive to the free volume. The relatively complex correlation between spectral data and FV makes this method more suitable for qualitative comparison of different polymers than for quantitative analysis of the FV [1,8]. 

The phenomenon of selective inhibition of chain reactions was for the first time explained by N.M. Emanuel, E.A. Bliunberg, L.A. Tavadyan and S.A. Maslov [11]. It was experimentally observed in a mnnber of liquid-phase oxidation reactions. Thus, introducing small amoimts of an additive stable nitroxyl radical (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPOL) and a heterogeneous inhibitor (WSc2) makes it possible to increase the selectivity of formation of imsaturated acids and epoxides in chain oxidation reactions of a-methylacrolein, 2-ethylhexenal, as well as co-oxidation of aldehydes and olefins (Table 5.1). 

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