Piperidine, 2,2,6,6-tetramethyl

Ethyl 1-naphthylacetate 1-Naphthaleneacetic acid, ethyl ester (8,9) (2122-70-5) Lithium 2,2,6,6-tetramethylpiperidide Piperidine, 2,2,6,6-tetramethyl-, lithium salt (9) (38227-87-1)... 

Piperidin-4-one, 1-hydroxy-2,2,6,6-tetramethyl-conformation, 2, 117 Piperidin-4-one, 2,2,6,6-tetramethyl-hydrochloride conformation, 2, 114... 

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... 

Chemical name(s) Dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-l-piperidine... 

Fig. 3 Detail of the O- - I interaction in the binary system associating the 4-amino-2,2,6,6-tetramethyl(piperidin-l-yloxyl) radical 7 with pTFDIB... 

In addition, Robbins and Eastman were able to trap the intermediate phenyl-acetyl radicals by photolysis in the presence of the 2,2,6,6-tetramethyl-piperidine-l-oxyl free radical,... 

The u.v.-visible spectrum of the 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl-methyl-cobinamide is very similar to methyl-cobin-amide itself and as a result this technique cannot be used to rigorously identify the spin labeled derivative. The spin labeled compound does show a spectral change with pH between pH 7.0 and pH 2.0 which methyl-cobinamide does not exhibit. Despite the similarities between methyl-cobinamide and nitroxylmethylcobinamide, the circular dichroism spectrum of the two derivatives are quite different. Fig. 23 shows the marked difference in C. D. spectra of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, methylcobinamide, and a methylcobinamide solution containing an equimolar amount of uncoordinated nitroxide. 

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... 

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>. 

Later on, other hydroxylamine derivatives such as 1-hydroxy-2,2,6,6-tetramethyl-4-oxo-piperidine (TEMPONEH) and l-hydroxy-3-carboxy-pyrrolidine (CP-3) have been used for superoxide detection [26]. It was found that these spin traps react with both superoxide and peroxynitrite and that they might be applied for quantification of these reactive species [27]. The CP-3 radical is less predisposed to reduction by ascorbic acid and therefore is probably more suitable for superoxide detection in biological systems. 

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. 

Registration of ROS was carried out by electron paramagnetic resonance (EPR) technique using spin trap l-hydroxy-2,2,6,6-tetramethyl-piperidine-4-OH (2 x 10 3 M). EPR spectra in the samples were registered at room temperature in quartz cuvette with the volume of 200 pi (Burlaka et al., 1994). 

Monobasic solutes that have no carbinyl hydrogens may also show nonequivalence. 3-Methyl-2-butanone, 4-methyl-2-pentanone, 2-methylpropanal, methyl 2-methylbutyrate, 2,2,6,6-tetramethyl-piperidine, methyldiisopropylcarbinol, and methylethyl-n-butyl-carbinol in TFAE-saturated benzene all show nonequivalence of sufficient magnitude (0.01-0,03 ppm) to allow nonequivalence sense determination at 220 MHz. An especially striking example is that provided by pyrazolines 26. With only a severalfold excess of (S)-TFAE, 3(5),5(S)-enriched samples of these compounds show nonequivalence in their methyl resonances (downfield sense for the singlets and upfield sense for the triplets) sufficient for enantiomeric purity determination at 90 MHz (52). 

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. 

The system RuCl3(PPh3)3/TEMPO/O3(10 atm air)/CgH3Cl (TEMPO=2,2, 6,6 -tetramethyl-piperidine-iV-oxyl radical. Fig. 1.40) oxidised primary alcohols to aldehydes and secondary alcohols to ketones. Hammett correlation studies and primary... 

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>. 

For a,a-dialkylamino acids enantiomerization is not a problem. The preparation of 4,4-dimethyl-2-[(9-fluorenylmethyl)oxy]-5(4F/)-oxazolone, an intermediate used in the synthesis of ( )-mirabazole C has been described. Recently, two new 2-aIkoxy-5(4F/)-oxazolones derived from Toac (2,2,6,6-tetramethyl-4-amino-l-oxy-piperidine-4-carboxylic acid) that incorporate Z or 9-fluorenylmethoxycarbonyl (Fmoc) protection at C-2 have been described. The Toac analogues were synthesized as part of a study of the crystal structure and ab initio calculations for these interesting systems. 

Distortion of the chair conformation by substitution occurs in 2,2,6,6-tetramethyl-piperidin-4-one hydrochloride (45) (71AX(B)932), in which steric interaction between axial methyl groups leads to flattening of the ring. The resultant C(2)—C(6) intramolecular distance is 3.2 A, to be contrasted with 2.4 A in the non-methylated compound. A similar effect is to be found in other 2,2,6,6-tetramethyl derivatives (81AX(B)1771). In the related free radical nitroxide (46) the steric interactions are reduced by adoption of a symmetric twist chair form (74AX(B)790). 4-Chloro-5-methylamino-2,3,6-pyridinetrione monohydrate... 

In order to find the initiation rate, a set of polymerizations, in the presence of inhibitor (2,2,6,6-tetramethyl-4-hydroxy-piperidine-l-oxy), was carried out. Inhibition period was measured for polymerization with poly(dimethylmethacrylate), polyethylene glycol, or without any template. The results are presented on the Figure 8.10. The plot of concentration vs. inhibition time is a straight line — the same for all experimental points. It means that initiation rate is the same, independent of the presence of tern-... 

Water-soluble iminoxyl free radical - 2,2,6,6,-tetramethyl-4-oxo-piperidin-l-oxyl (commercial trade name TEMPON) was used as a paramagnetic probe. 

Observations Poly(2,2,6,6-tetramethyl piperidine-4-vinyloxy-l-oxyl) was prepared... 

---