Azobis ethers

The radical alkylation of ketones is achieved by their conversion into the desired N-silyloxy enamines 81 (Scheme 13). The reaction of 81 with diethyl bromomalonate in the presence of EtsB (0.5 equiv) in benzene was performed in open air and stirred at room temperature for 3h. With nitro compounds it is achieved by their conversion into the desired ]V-bis(silyloxy)enamines (82) (Scheme 13). When the reaction is carried out with 82 and alkyl iodides with an electron-withdrawing substituent at the a-position, using V-70 as radical initiator (2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile)), it underwent a clean radical alkylation reaction to yield an oxime ether. Successful radical alkylation of... 

If the photoequilibrium concentrations of the cis and trans isomers of the photoswitchable ionophore in the membrane bulk and their complexation stability constants for primary cations are known, the photoinduced change in the concentration of the complex cation in the membrane bulk can be estimated. If the same amount of change is assumed to occur for the concentration of the complex cation at the very surface of the membrane, the photoinduced change in the phase boundary potential may be correlated quantitatively to the amount of the primary cation permeated to or released from the membrane side of the interface under otherwise identical conditions. In such a manner, this type of photoswitchable ionophore may serve as a molecular probe to quantitatively correlate between the photoinduced changes in the phase boundary potential and the number of the primary cations permselectively extracted into the membrane side of the interface. Highly lipophilic derivatives of azobis(benzo-15-crown-5), 1 and 2, as well as reference compound 3 were used for this purpose (see Fig. 9 for the structures) [43]. Compared to azobenzene-modified crown ethers reported earlier [39 2], more distinct structural difference between the cis... 

To conclusively disprove the involvement of the chromanol methide radical, the reaction of a-tocopherol with dibenzoyl peroxide was conducted in the presence of a large excess of ethyl vinyl ether used as a solvent component. If 5a-a-tocopheryl benzoate (11) was formed homolytically according to Fig. 6.6, the presence of ethyl vinyl ether should have no large influence on the product distribution. However, if (11) was formed heterolytically according to Fig. 6.9, the intermediate o-QM 3 would be readily trapped by ethyl vinyl ether in a hetero-Diels-Alder process with inverse electron demand,27 thus drastically reducing the amount of 11 formed. Exactly the latter outcome was observed experimentally. In fact, using a 10-fold excess of ethyl vinyl ether relative to a-tocopherol and azobis(isobutyronitrile) (AIBN) as radical... 

N-4-(Pyridyl) bis(methacrylimide) (8.6 g, 37 mmol) was dissolved in dimethylformamide (35 ml). The solution was degassed under argon and azobis(isobutyronitrile) (0.4 g, 2 mmol) was added. The reaction mixture was heated to 75°C under argon. After 24 hrs, another portion of AIBN (0.4 g, 2 mmol) was added and the reaction continued for another 24 hrs. The resulting polymer was isolated by precipitation from ether in 65% yield. DSC of the polymer indicated a Tg at 110°C. TGA showed onset of... 

The EtsSiH/tetracyanoethylene combination reduces acetals and ketals to the corresponding ethers but the yields are mixed.500 The full reduction of benz-aldehyde acetals to the toluene derivatives is realized by the initial reduction with Et3SiH/SnBr2-AcBr followed by Bu3SnH/AIBN (azobis(isobutyronitrile)) or LiAlH4.479 The overall yields are excellent. 

Tin-based reagents are not always snitable owing to the toxicity of organotin derivatives and the difficulties often encountered in removing tin residues from the final product. Therefore, the same authors have carried out additional experiments with 17d and several different alkyl halides under tin-free conditions. The treatment of 16d with tert-butyldiphenylsilyl chloride (TBDPSCl) and triethylamine in the presence of silver triflate in CH2CI2 affords the bis(silyloxy)enamine 17d in 92% yield (Scheme 17). When the radical reaction was carried out with ethyl iodoacetate in the presence of 2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as the initiator in CH2CI2, the oxime ether 19 was obtained in 83% yield (Scheme 17). 

Because the size of the emulsion droplets dictates the diameter of the resulting capsules, it is possible to use miniemulsions to make nanocapsules. To cite a recent example, Carlos Co and his group developed relatively monodisperse 200-nm capsules by interfacial free-radical polymerization (Scott et al. 2005). Dibutyl maleate in hexadecane was dispersed in a miniemulsion of poly(ethylene glycol)-1000 (PEG-1000) divinyl ether in an aqueous phase. They generated the miniemulsion by sonication and used an interfacially active initiator, 2,2 -azobis(A-octyl-2-methyl-propionamidine) dihydrochloride, to initiate the reaction, coupled with UV irradiation. 

For this puq)ose, the photoswitchable bis(crown ether)s 88 and 89 as well as the reference compound 90 have been synthesized. Compounds 88 and 89 are highly lipophilic derivatives of azobis(benzo-15-crown-5). The parent azobis crown ether was originally developed by Shinkai and its photoresponsive changes in complexation, extraction, and transport properties thoroughly examined. Compared to 87, more distinct structural difference between the cis and trans isomers can be expected for 88 and 89 because in the latter compounds the 15-crown-5 rings are directly attached to the azobenzene group. The photoequilibrium concentrations of the cis and trans forms and the photoinduced changes in the complexation constants for alkali metal ions are summarized in Table 7. 

A 200-ml flask was charged with ethylene glycol monobutyl ether (30 g) and then heated to 85°C and treated with the step 4 product (40 g) and 2,2 -azobis(2,4-dimethylvaleronitrile) (1.5 g) over a period of 4 hours. Thereafter, a mixture of ethylene glycol monobutyl ether (30 g) and 2,2 -azobis(2,4-dimethylvaleronitrile) (0.5 g) was added over a period of 3 hours in the identical manner. After stirring an additional hour, the mixture was cooled to ambient temperature and a viscous liquid obtained. The percent solids of the liquid was 40.3% with a 98% reaction conversion. 

A solution of the step 2 product (1.0 g), methyl methacrylate (6.2 g), and 2,2 -azobi-sisobutyronitrile (0.06 g) dissolved in 60 ml of 1-pentanol was deoxygenated and then heated to 70°C for 24 hours. The product was isolated after precipitating from diethyl ether and drying in an oven at 50°C. 

A 25-ml Schlenk tube was charged with the step 2 product mixture (1.76 or 2.00 g) dissolved in 2 or 9 ml of either THF or toluene. All samples were free radically initiated using either 2,2 -azobis(isobutyrylnitrile) (Vazo 64) or l,l -azobis(cyclo-hexanecarbonitrile) (Vazo 88). Each tube was then sealed with a rubber septum and then degassed by three cycles of freeze-thaw pumping and then heated to 60°C for selected times. After cooling to ambient temperature, the mixture was precipitated in 20 ml petroleum ether and then isolated and washed with cold petroleum ether and the product isolated. 

A-Vinyl-2-pyrrolidone (1.8 mol), 2,2 -azobis(2-methyl-N-(2-hydroxyethyl)-propio-namide) (0.018 mol), and 2-mercaptoethanol (0.072 mol) were dissolved in 3000 ml of 2-propanol degassed for 1 hour. The free radical polymerization was carried out at reflux while stirring for 44 hours. The mixture was concentrated and then dissolved in 400 ml of 4-methyl-2-pentanone and slowly precipitated into 5000 ml of t-butyl methyl ether. The suspension was filtered and the filter cake washed twice with 200 ml of -butyl methyl ether. The solid was purified by dissolving in 400 ml of... 

The bisbarium complex of azobis(berizo-18-crown-6) ether 28 exhibits catalytic properties that can be reversibly activated-deactivated by light-induced changes in molecular geometry [32]. The azobenzene unit is a well-known photochromic [33], often used in the construction of molecular switches [34]. 

A series of azobis(benzocrown ethers) called butterfly crown ethers such as 9 and 10 were synthesized [11-15]. The photoresponsive molecular motion is... 

Shinkai et al.111-151 synthesized a series of azobis(benzocrown ethers) called butterfly crown ethers , of which compounds 9 and 10 are examples. Their photoresponsive molecular motion resembles that of a flying butterfly. It was found that the proportion of their Z forms at the photostationary state increases remarkably with increasing concentration of Rb+ and Cs+, which interact with two crown rings in a 1 2 sandwich fashion. This is clearly due to the bridge effect of the metal cations with the two crowns, results that support the view that the Z forms make an intramolecular 1 2 complex with these metal cations. As expected, the Z forms extracted alkali metal cations with large ion radii more efficiently than did the corresponding E forms. In particular, the photoirradiation effect on 9 is quite remarkable for example, ( )-9 (n= 2) extracts Na+ 5.6 times more efficiently than (Z)-9 (n= 2), whereas (Z)-9(n= 2) extracts K+ 42.5 times more efficiently than ( )-9(n= 2). l ... 

Recently, carboxyl- and amino-functionalized polystyrene latex particles were synthesized by the miniemulsion copolymerization of styrene and acrylic acid or 2-aminoethyl methacrylate hydrochloride (AEMH) [70, 71]. The reaction was started by using an oil-soluble initiator, 2,2 -azobis(2-methylbutyronitrile) (V-59). Two types of surfactant, i.e., ionic negatively charged SDS or positively charged CTMA-Cl, and nonionic Lutensol AT50 (which is a PEO hexadecyl ether with an EO block length of about 50 units) were used to stabilize the initial droplets and final particles. 

Ac, acetyl AIBN, azobis(isobutanonitrile) All, allyl AR, aryl Bn, benzyl f-BOC, ferf-butoxycarbonyl Bu, Butyl Bz, benzoyl CAN, ceric ammonium nitrate Cbz, benzyloxycarbonyl m-CPBA, m-chloroperoxybenzoic acid DAST, diethylaminosulfur trifluoride DBU, l,8-diazabicyclo[5.4.0]undec-7-ene DCC, /V. /V - d i eye I oh e x y I c ar bo -diimide DCM, dichloromethyl DCMME, dichloromethyl methyl ether DDQ, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone DEAD, diethyl azodicarboxylate l-(+)-DET, L-(+)-diethyl tartrate l-DIPT, L-diisopropyl tartrate d-DIPT, D-diisopropyl tartrate DMAP, 4-dimethylaminopyridine DME, 1,2-dimethoxyethane DMF, /V./V-dimethylformamide DMP, 2,2-dimethoxypropane Et, ethyl Im, imidazole KHMDS, potassium hexamethyldisilazane Me, methyl Me2SO, dimethyl sulfoxide MOM, methoxymethyl MOMC1, methoxymethyl chloride Ms, methylsulfonyl MS, molecular sieves NBS, N-bromosuccinimide NIS, /V-iodosuccinimide NMO, /V-methylmorpho-line N-oxide PCC, pyridinium chlorochromate Ph, phenyl PMB, / -methoxvbenzyl PPTs, pyridiniump-toluenesulfonate i-Pr, isopropyl Py, pyridine rt, room temperature TBAF, tetrabutylammonium fluoride TBS, ferf-butyl dimethylsilyl TBDMSC1, f-butylchlorodimethylsilane Tf, trifhioromethylsulfonyl Tf20, trifluoromethylsulfonic anhydride TFA, trifluoroacetic acid THF, tetrahydrofuran TMS, trimethylsilyl TPAP, tetra-n-propylammonium perruthenate / -TsOH. / -toluenesulfonic acid... 

Indeed, 4,4 -azobis-(4-cyanopentanoyl)-bis-benzoin (ACPB) and 4,4 -azobis-(4-cyano ntenoyl)-bis-(a-methylolbenzoin methyl ether) (ABME) have been used in the synthesis of poly(styrene )s possessing benzoin or benzoin methyl ether end groups (Scheme 38) ... 

S. Shinkai, K. Shigematsu, M. Sato and O. Manabe, Photoresponsible crown ethers. Part 6. Ion transport mediated by photoinduced cis-trans interconversion of azobis-(benzocrown ether), J. Chem. Soc., Perkin Trans. I, 1982, 2735-2739 J. Anzai, H. Sasaki, A. Ueno and T. Osa, Photo-induced potential changes across poly(vinyl chloride)-crown ether membranes, J. Chem. Soc., Chem. Commun., 1983, 1045 J. Anzai, H. Sasaki, K. Shimokawa, A. Ueno and T. Osa, Photocontrol of alkali metal ion permeability through the poly(vinyl chloride)/crown ether membranes, Nippon Kagaku Zasshi, 1984, 338. 

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