Dimethyl tetramethylpiperidine

Due to their tendency to form (Z)-enolates, ketones usually provide syn-aldols, and anti-se ec-tive chiral ketone enolates are rare. When, however, (S)-5,5-dimethyl-4-trimethylsiloxy-3-hex-anone is deprotonated with (V-(bromomagnesio)-2,2,6,6-tetramethylpiperidine, the (E)-enolate la is assumed to be formed. Subsequent addition to aldehydes delivers anh-aldols 2a and 3a in ratios of between 92 8 and 95 5 and yields of 75-85%53b. 

On the other hand, the predominant formation of the diastereomeric aldols 3 b results from the titanium enolate 1 b of (S )-5,5-dimethyl-4-tert-butyldimethylsilyloxy-3-hexanone. For this purpose, the ketone is first deprotonated with A-(bromomagnesio)-2,2,6,6-tetramethylpiperidine and the magnesium enolate, presumably (E) configurated, formed is thereby treated with hexamethylphosphoric triamide and triisopropyloxytitanium chloride. After sonification, the aldehyde is added to give predominantly aldol adducts 3b the diastereomeric ratio of 3b/2b surpasses 95 5 and the chemical yields range from 85 to 88%53b. 

All the aforementioned evidence for cluster formation is indirect. In this laboratory we have recently observed a special type of cluster formation that supports the notion that such clusters may exist. Rey and McConnell41 have described the preparation of two spin labels, N,N -dipalmitoyl-N,N -bis-(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-l, 10-diaminodecane (VII) and N,N -dimethyl-N,N -dihexadecyl-N,N -bis-(l-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-1,10-diammoniumdecane diiodide (VIII). 

In a subsequent investigation, the author, (3), prepared the nitroxide-mediated polymerization agent, 4,4-dimethyl-2- [ 1 -(2,2,6,6-tetramethylpiperidin-1 -yloxy)-ethyl] -4H-oxazol-5-one, (I), as a method of preparing telechelic polymers. 

Commercially important polyesters, e.g. poly[l-(2-ethylenyl)-2,2,6,6-tetramethyl-4-piperidinylbutane dioate] (146) [190] were synthesized from l-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidines and suitable dicarboxylic acids. Another polymeric HALS was prepared by transesterification of oligoesters of tetramethyl-butane-l,2,3,4-tetracarboxylate with 22,6,6-tetramethyl-4-hydroxypiperidine and 1,10-decanediol [191]. Compound 147 is a similar polyester type HALS. An ester-amide chain is created during esterification of 2-(2,2,6,6-tetramethyl-4-piperidinylamino)ethanol and dimethyl adipate [192]. 

Ozone is a dangereous deteriogen for unsaturated polymers. Its role in oxidation of PO is rather underrated. Little information is available on the influence of O3 on HAS. Photo-ozonization of tetramethylpiperidine yielded in the first step the respective nitroxide [223], 2,6-Dimethyl-2-hydroxy-6-nitroheptane 142 was isolated in 91-98% yield ... 

It has been reported that living radical polymerization of 4-acetoxystyrene with a TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl) adduct as the initiator, followed by base hydrolysis produces PHOSTs with narrow polydispersity, 1.1-1.4, which tend to have a 10-20°C higher 7g than their conventional PHOST counterparts (with polydispersity of 2.0-2.4), whose 7g ranges from 140 to 180°C. Hirao et al. have demonstrated the synthetic route to monodisperse PHOST, involving the living anionic polymerization of 4-tert-butyl(dimethyl)siloxystyrene... 

Fig. 2 Chemical structures of common nitroxide spin probes Fremy s salt (potassium nitrosodi-sulfonate) TEMPO and derivatives (2,2,6,6-tetramethylpiperidine-l-oxyl), DOXYL (4,4-dimethyl-oxazolidine-l-oxyl) PROXYL (2,2,5,5-tetramethylpyrrolidine-l-oxyl) Dehydro-PROXYL (2,2,5,5-tetramethylpyrroline-l-oxyl) 5-DSA (5-DOXYL stearic acid) 16-DSA (16-DOXYL stearic...

Since its discovery in 1993 [27], nitroxide-mediated polymerization (NMP) has been the most extensively studied technique from the dissociation-combination dass of LRP mechanisms (Scheme 13.7). This method is also commonly termed stable free radical polymerization (SFRP). NMP reactions are distinguished by the use of stable free radical nitroxide molecules (N ) as the controlling agent [e.g. 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO), (l-diethylphosphono-2,2-dimethyl)propyl nitroxide (DEPN)]. 

Cl H2bN5S3, 2-(1-Isopropyl-3,5-dimethyl-4,6-dithioxo-hexahydro-l,3,-5-triazine-2-ylideneamino)-N,N-dimethylthioisobutyramide, 43B, 302 Cl4H26N2 f 1,4-Bis(1,2,2-trimethylvinyl)piperazine, 45B, 238 C14H2 9NO, 4-t-Butyl-4-hydroxy-2,2,6,6-tetramethylpiperidine, 46B,... 

HYDROXYETHYL)-4-HYDROXY-2.2,6,6-TETRAMETHYLPIPERIDINE-SUCCINIC ACID. DIMETHYL ESTER, COPOLYMER (M.W.1500-5000)... 

Deprotonative alkylation of arene C-H bonds by alkyl iodides and bromides is achieved in the presence of catalytic amounts of iron(III) chloride, /ra s-A,Ar-dimethyl-cyclohexane-1,2-diamine, and 2,2,6,6-tetramethylpiperidin-l-ylmagnesium chloride lithium chloride complex (TMPMgCl LiCl) as a base. Furans, thiophenes, pyridines, and some electron-deficient arenes can be employed in this reaction (Scheme 4-241). ... 

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