Tetramethyl piperidine oxide

The olefin metathesis of 3-hydroxy-4-vinyl-l,2,5-thiadiazole 112 and a McMurry coupling reaction (Ti3+ under reductive conditions) of the aldehyde 114 were both unsuccessful <2004TL5441>. An alternative approach via a Wittig reaction was successful. With the use of the mild heterogenous oxidant 4-acetylamino-2,2,6,6-tetramethyl-piperidine-l-oxoammonium perfluoroborate (Bobbitt s reagent), the alcohol 113 was converted into the aldehyde 114. The phosphonium salt 115 also obtained from the alcohol 113 was treated with the aldehyde 114 to give the symmetrical alkene 116 (Scheme 16) <2004TL5441>. 

As expected, 2-halo-l,3-dithianes react with nucleophiles under Sn conditions. Suitable nucleophiles are enamines <2002TL9517, 2004T6931> and phenols <1997MOL7>. The reaction with EtOC(S)S K, followed by oxidation, provided a xanthate which generated a 1,3-dithiane 1-oxide radical upon treatment with Bu3SnH (Scheme 69) <2004T7781>. An efficient one-carbon radical precursor has also been obtained by addition of 2,2,6,6-tetramethyl-piperidine-l-oxyl (TEMPO) to 2-lithio-l,3-dithiane. The reactivity of this compound has been demonstrated <2005S1389>. 

Optically active (—)-sparteine, a piperidine-derived alkaloid complexed with palladium chloride 33, has been used in the enantioselective oxidation of benzyl alcohol derivatives <2005JA14817>. 4-Hydroxy-TEMPO 34 serves as an efficient catalyst for the continuous production of aldehydes from alcohols and bleach in a tube reactor (TEMPO = 2,2,6,6-tetramethyl-piperidine-l-oxyl) <20050PD577>. 

However, PEG supported metal-free catalysts have also been shown to perform well in water. For example the synthesis of a PEG-supported TEMPO (2,2,6,6-tetramethyl-piperidine-l-oxyl), and its use as a highly efficient, recoverable and recyclable catalyst in oxidation reactions was described (Pozzi et al. 2004). 

Benzeneselenol is an extremely fast reducing agent for alkyl radicals. The rate constant for benzeneselenol trapping of alkyl radicals is 1.2 x 10 s at 20 °C [99]. This is faster than the coupling reaction of alkyl radicals with 2,2,6,6-tetramethyl-piperidine-N-oxide (TEMPO) [100]. This exceptionally large rate constant makes benzeneselenol a very useful radical clock for the measurement of very fast radical processes [99]. 

Triacetonamine and 2,2,6,6-tetramethyl-4-piperidinol are oxidized by the hydrogen peroxide-sodium carbonate system very selectively, giving practically a quantitative yield (45). For amine oxidation, the hydrogen peroxide-acetonitrile system is often effective enough (46,47), while for hindered piperidine oxidation, peracids can be also used. 

Auch Platin(IV)-oxid kann verwendet werden, so z. B. bei der Hydrierung von 4-Ath-oxycarbonylhydrazono-2,2,6,6-tetramethyl-piperidin (Athanol/Essigsaure, 20°/3 bar) zum 4-(2-Athoxycarbonyl-hydrazino)-2,2,6,6-tetramethyl-piperidin (52% d.Th.)1. Zur analogen Reaktion der Athoxycarbonyl-hydrazone von 3-Phenyl-butanon-(2) und (2-Chlor-phenyl)-aceton s. Lit.2. 

Selective oxidation of primary OH groups in carbohydrate derivatives has been achieved using A -oxoammonium salts generated from (2,2,6,6-tetramethyl-piperidin-l-yl)oxy (TEMPO) and its derivatives as catalysts. The stoichiometric oxidants employed include sodium hypochlorite [48-50], sodium hypobromite [51, 52], and ammonium peroxodisulfate (using silver on alumina as a co-catalyst) [53, 54]. A representative protocol is shown in Scheme 12. 

Conversion of substituted benzoins to corresponding benzils occurs in quantitative yield when ZnO—DABCO eomplex is used to catalyse aerobic oxidation by O2 in toluene in the presence of K2CO3. The use of chiral ligand (118), in the presence of ZnS04 7H20 and 4-acetylamino-2,2,6,6-tetramethyl-piperidine-l-oxoammonium perchlorate (TEMPO), resulted in isolation of benzil along with enantiomerically enriched benzoin (43% ee). ... 

The oxoammonium is generated in situ from its precursor, 2,2, 6,6 -tetramethyl-piperidine-N-oxyl (TEMPO), or derivatives thereof, which is used in catalytic quantities (see Figure 5.2). Various oxidants can be applied as the final oxidant [7-12]. In particular, the TEMPO-bleach protocol using bromide as co-catalyst introduced by Anelli et al. is finding wide application in organic synthesis [7]. TEMPO is used in amounts as low as 1 mol% relative to the substrate, and full conversion of substrates can commonly be achieved within 30 min. 

Piperidin-4-one N-oxide, 2,2,6,6-tetramethyl-solvent effects, 2, 146 Piperidinones stability, 2, 159-161 synthesis, 2, 81, 95 from S-aminopentanoic acids, 2, 402 Piperidin-2-ones IR spectroscopy, 2, 130 synthesis... 

Rearangement of furoxans leads to the formation of new heterocyclic systems derivatives of triazoles, diazoles, isoxazoles, and pyrimidinones. For example, on the basis of the experimental results using labeled compound 52-15N , the formation of 8-phenyltheophylline 53, the 1,3-dimethylalloxazines (54 n = 0, 1), and l,3,7,9-tetramethyl-l//,9//-pyrimido[5,4-g]-pteridine-2,4,6,8-tetraone 55 in the thermal reaction of the iV-oxide 52 with benzylamine, aniline, or piperidine and the generation of NO or NO-related species in the reaction with iV-acetylcysteamine were reasonably explained by... 

It is known that the nitrosonium cation is a strong oxidant (54). In (55) it was found by multinuclear NMR ( H, 13C, 19F and 14N) that the interaction of nitrosonium tetrafluoroborate with 2,2,6,6-tetramethyl-4-R-piperidine-1 -oxyl radicals 22a-e resulted in formation of 4-R-2,2,6,6-tetramethylpiperidine-l-oxoammonium tetrafluoroborates (Scheme 16). Cations 23a-e could be classified as nitrosonium complexes of biradicals 24a-e. 

While in most of the reports on SIP free radical polymerization is utihzed, the restricted synthetic possibihties and lack of control of the polymerization in terms of the achievable variation of the polymer brush architecture limited its use. The alternatives for the preparation of weU-defined brush systems were hving ionic polymerizations. Recently, controlled radical polymerization techniques has been developed and almost immediately apphed in SIP to prepare stracturally weU-de-fined brush systems. This includes living radical polymerization using nitroxide species such as 2,2,6,6-tetramethyl-4-piperidin-l-oxyl (TEMPO) [285], reversible addition fragmentation chain transfer (RAFT) polymerization mainly utilizing dithio-carbamates as iniferters (iniferter describes a molecule that functions as an initiator, chain transfer agent and terminator during polymerization) [286], as well as atom transfer radical polymerization (ATRP) were the free radical is formed by a reversible reduction-oxidation process of added metal complexes [287]. All techniques rely on the principle to drastically reduce the number of free radicals by the formation of a dormant species in equilibrium to an active free radical. By this the characteristic side reactions of free radicals are effectively suppressed. 

Some features of the behavior of 2,2,6,6-tetramethyl-4-piperidone oxime (39) (X = H) and its oxidized derivatives (X = OH, X = 6) in the reaction with acetylene in KOH/DMSO (Scheme 22) are discussed (88KGS3S0) along with experimental details dealing with the synthesis of new pyrrolo[3,2-c]piperidines (40), previously reported either briefly (84MI2) or in general (86ZC41). 

Primary alcohol groups can be exclusively oxidized to aldehyde groups with pyridinium dichromate [149,150] and to carboxyl groups with the 2,2,6,6-tetramethyl-1-piperidine oxoammonium ion (TEMPO) [151]. The aldehydes can then be reduced to primary alcohols by reaction with NaB H4 [150,152], giving radiolabeled H-starch and the carboxyl group can be inverted by the action of Azotobacter vinlandii poly- 8-D-marmuronic acid C-5-epimerase to give L-iduronic acid [153]. 

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