2,2,6,6-tetramethylpiperidine N-oxide

Spectroscopic techniques such as electron spin resonance (ESR) offer the possibility to "probe" the chemical environment of the interlayer regions. With the ESR technique, an appropriate paramagnetic ion or molecule is allowed to penetrate the interlayer, and chemical information is deduced from the ESR spectrum. Transition metal ions, such as Cu2+, and nitroxide radical cations, such as TEMPAMINE (4-amino-2,2,6,6-tetramethylpiperidine N-oxide) have been used as probes in this manner (6-14). Since ESR is a sensitive and non-destructive method, investigations of small quantities of cations on layer silicate clays at various stages... 

Reactions of Germylenes with Stabilized Radicals. The stable germylene Ge[C4H4(SiMe3)4] reacts with 2 equivalents 2,2,6,6-tetramethylpiperidine N-oxide (TEMPO, -ONR2) to... 

SCHEME 11.3 Random copolymerization of propylene with TEMPO-functionalized alkenes (TEMPO tetramethylpiperidine N-oxide). The product is suitable for heat-induced radical grafting of styrene. 

Tetramethylpiperidine-N-oxide(Tempo) traps R but not the Co(IT) unit in a Costa-type model B12 system, and has been used by Finke s group to obtain kinetic parameters for reaction (17) for R = PhCH2 and Mc3CH2 (see Table 11.2). (Further data on the saloph, cobalamin, and... 

We wish to report here on a new and highly efficient catalyst composition for the aerobic oxidation of alcohols to carbonyl derivatives (Scheme 1). The catalyst system is based on 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO), Mg(N03)2 (MNT) and N-Bromosuccinimide (NBS), utilizes ecologically friendly solvents and does not require any transition metal co-catalyst. It has been shown, that the described process represents a highly effective catalytic oxidation protocol that can easily and safely be scaled up and transferred to technical scale. 

The mechanism of the aerobic oxidation of alcohols depends on the particular catalyst used. Two general mechanisms can be considered (1) the direct oxygenation of alcohols by 02 through a free-radical chain process initiated by the catalyst, and (2) the direct oxidation of the alcohol by the catalyst, which is then regenerated by 02. Both mechanisms are well illustrated [6] by the aerobic oxidations catalyzed by the persistent tetramethylpiperidine-N-oxyl (TEMPO) radical 1 and the nonpersis-tent phthalimide-N-oxyl (PINO) radical 2. 

Table 14 Solvent Effects in ESR Spectra of 2,2,6,6-Tetramethylpiperidin-4-one N-Oxide (159)...

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. ... 

FD-MS oxidation studies of N-alkyl-3,3-dialkyldecahydroquin-oxalin-2-ones show that only the N-oxide form and no hydrogen atoms are lost. Similarly, the oxidation of 2,2,6,6-tetramethylpiperidines gives only the nitroxyl radical and no hydrogen atoms are lost. The facts prove that both a nitroxyl radical and hydrogen atoms on the bicyclic bridge are necessary for the oxidation of the hydrogen atoms to occur. 

TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) as an important reagent in alcohol oxidation and its application in synthesis of natural products between 2000 and 2004 06MRO155. 

Highly efficient rhodium-catalyzed direct arylations were accomplished through the use of 2,2, 6,6 -tetramethylpiperidine-N-oxyl (TEMPO) as terminal oxidant [17]. Thereby, a variety of pyridine-substituted arenes was regioselectively functionalized with aromatic boronic acids (Scheme 9.5). However, in order for efficient catalysis to proceed, 4equiv. of TEMPO were required. The use of molecular oxygen as terminal oxidant yielded, unfortunately, only unsatisfactory results under otherwise identical reaction conditions. However, a variety of easily available boronic acids could be employed as arylating reagents. 

Pyridylbenzenes are directly ortfio-arylated with tetra-arylstannanes in the presence of a rhodium(I)-phosphine complex as catalyst [140]. A mechanistic pathway was proposed based on the oxidative addition of a rhodium] I) complex to the ortho position of the phenyl ring directed by the pyridine nitrogen, followed by arylation by the tetra-arylstannane. A somewhat related reaction of arylboronic acids was achieved with a [RhCl(C2H4)2]2/P[p-(CF3)QH4]3 catalyst system [141]. In this instance, the 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) radical was used as a stoichiometric oxidant. Arylboronic acids also arylate benzophenone imines in the presence of Rh(I) catalysts [142]. 

A soln. of 85%-m-chloroperoxybenzoic acid in methylene diloride added to a stirred ice-cooled soln. of 5-norbornen-2-ol in the same solvent, after 2 hrs. treated with a soln. of 2,2,6,6-tetramethylpiperidine hydrochloride in methylene chloride followed by additional m-chloroperoxybenzoic acid soln., and the product isolated after 1.5 hrs. exo-5,6-epoxy-2-norbornanone. Y 86%. J. A. Celia, J. A. Celia, J. A. Kelley, and E. F. Kenehan, J. Org. Chem. 40, 1860 (1975) oxidation of alcohols with N-oxide radicals cf. B. Ganem, ibid. 40, 1998 ketones from sec. alcohols with m-chloroperoxybenzoic acid/HCl cf. J. A. Celia, J. P. McGrath, and S. L. Regen, Tetrah. Let. 1975, 4115 review of N-oxide radicals s. H. G. Aurich and W. Weiss, Topics Curr. Chem. 59, 65 (1975). 

The iodine atom in a 2-deoxy-2-iodo-gIycoside can be replaced by a hydroxyl group by radical deiodination in the presence of 2,2,6,6-tetramethylpiperidine-A -oxide, resulting in adducts such as 88 and its C-2 epimer, the N-0 bond in which can then be reductively cleaved (Zn, HOAc). ... 

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