A-acetoxystyrene

Another example is that of a-acetoxystyrene (7.13), which yields acetic acid and acetophenone (7.14) upon hydrolysis. This compound is quite stable... 

J. P. Patel, A. J. Repta, Enol Esters as Potential Prodrugs. I. Stability and Enzyme-Mediated Hydrolysis of a-Acetoxystyrene , lnt. J. Pharm. 1980, J, 329-333. 

Recently, Noyce and Pollack306 have found kinetic evidence for a changeover from acyl to alkyl-oxygen cleavage in the hydrolysis of a-acetoxystyrenes. At low acidities (1 M H2S04) compounds with electron-withdrawing substituents are hydrolyzed in a reaction which behaves as expected for the Aac2 mechanism. The solvent deuterium isotope effect, kH/kD = 0.75, and the effect of substituents on the rate is small. As the acidity of the medium is increased... 

Also, a-fluoroketones were prepared from a-acetoxystyrene and l-acetoxy-3,4-dihy-dronaphthalene [39,40] ... 

Poly(a-acetoxystyrene) is an acetophenone enol ester and its acidolysis involves the polymer backbone in contrast to the side chain deprotection discussed earlier (Fig. 30). Protonation of the side chain carbonyl oxygen results... 

Frequently used substrates include a-acetoxystyrene (AXS) and a-acet-amidostyrene (AS). Hydrogenation of enol esters leads to chiral acetates, which can be easily hydrolysed to the parent alcohols. Hydrogenation of enamides is equally interesting because the obtained amines are extremely important synthetic precursors. Some results with those and related substrates are listed in Table 7.3. 

Electrochemical fluorination of olefins provides mono- and/or difluorinated products. In the cases of a-acetoxystyrene and 1-acetoxy-3,4-dihydronaphthalene, the corresponding a-fluoroketones are formed as shown in Scheme 3 [7],... 

The oxidative coupling of alkenes which have two substituents at the 2 posi-tion, such as isobutylene, styrene, 2-phenylpropene, 1,1-diphenylethylene, and methyl methacrylate, takes place to give the 1,1,4.4-tetrasubstituted butadienes 285 by the action of Pd(OAc)2 or PdCF in the presence of sodium acetate[255-257]. Oxidation of styrene with Pd(OAc)2 produces 1.4-diphenylbutadiene (285, R = H) as a main product and a- and /3-acetoxystyrenes as minor pro-ducts[258]. Prolonged oxidation of the primary coupling product 285 (R = Me) of 2-phenylpropene with an excess of Pd(OAc)2 leads slowly to p-... 

In some instances, the resist polymer can be prepared in a single step by direct polymerization of the protected monomer(s) (37,88), entirely avoiding the intermediate PHOST. HOST-containing resist polymers have also been prepared by free-radical copolymerization of a latent HOST and a stable, acid-labile monomer, eg, the copolymerization of acetoxystyrene with tert-huty acrylate, followed by selective removal of the acetoxy group (89) (Fig. 30). 

Several 4-(3-alkyl-2-isoxazolin-5-yl)phenol derivatives that possess liquid crystal properties have also been obtained (533-535). In particular, target compounds such as 463 (R = pentyl, nonyl) have been prepared by the reaction of 4-acetoxystyrene with the nitrile oxide derived from hexanal oxime, followed by alkaline hydrolysis of the acetate and esterification (535). A homologous series of 3-[4-alkyloxyphenyl]-5-[3,4-methylenedioxybenzyl]-2-isoxazolines, having chiral properties has been synthesized by the reaction of nitrile oxides, from the dehydrogenation of 4-alkyloxybenzaldoximes. These compounds exhibit cholesteric phase or chiral nematic phase (N ), smectic A (S4), and chiral smectic phases (Sc ), some at or just above room temperature (536). 

A reactor flask was charged with methacrylate ester of 9-anthracene methanol (4.2 g), 4-acetoxystyrene (13.8 g), 2,2 -azobisisobutylonitrile (0.8 g), and propyleneglycol monomethylether and then vented for 15 minutes. The reaction mixture was then heated to 70°C for 5 hours and then cooled to ambient temperature and treated with 26 wt% aqueous tetramethylammonium hydroxide (7 g). The reaction temperature was then raised to 40°C for 3 hours and then further raised to 60°C for 8 hours. The mixture was then recooled to ambient temperature and acidified to a pH of 6 using acetic acid. The polymer was precipitated in 600 ml of methanol and the solid filtered, washed with methanol and deionized water, and dried. The precipitated polymer was redissolved in propyleneglycol monomethylether (60 g) and reprecipitated in 600 ml methanol. The solid was refiltered, rewashed, dried at 40°C, and the product isolated having an Mw of 12,800 Da with an Mn of 5400 Da. 

This reaction sequence is satisfactory although the overall yield is approximately 50%. A different route for the preparation of poly(p-acetoxystyrene) involves the direct acetylation of poly (p-hydroxystyrene) with acetic anhydride. The main problem with this approach is the lack of commercial availability of high purity poly(p-hydroxystyrene). 

Reactive Pendant Groups on Styrene Backbones. The photolysis of p-acetoxystyrene (III) in acetonitrile solution gives results which are similar to those obtained in a comparable study in the solid-state using 1 /tm thick films in both cases the expected rearrangement is taking place as shown on Scheme 7. 

Fries rearrangement of aromatic formate esters suggests that phenols are the major products (.24) obtained in the reaction. As poly(p-hydroxystyrene) is remarkably clear in the deep UV, it is likely that poly(p-formyloxystyrene) will not suffer from the same problem of photostabilization upon exposure as was the case with poly (p-acetoxystyrene). This expectation was confirmed by our study of the photo-Fries reaction of p-cresyl formate no ortho rearranged product was isolated after reaction while p-cresol and a small amount of starting material were obtained. 

Preparation of p-Acetoxystyrene This compound was prepared by a modification of the procedure of Corson et al. (14), using p-hydroxyacetophenone as a starting material. Fractional distillation of the crude material gave a 46% yield of p-acetoxystyrene with b.p. 69-72 °C/0.5 mm Hg (lit. 73-75°C/0.6 mm Hg14). 

Preparation of Poly(p-Acetoxystyrene) (III) A 9.95 g aliquot of p-acetoxystyrene and 0.0997 g AIBN were added to 60 ml of toluene in a 100 ml 2-necked round-bottomed flask equipped with a water-cooled condenser, nitrogen inlet and outlet. The mixture was heated to 70-75"C under nitrogen for 24 hours. Precipitation of the polymeric solution in methanol and subsequent filtering and washing with additional methanol gave a white powder. Drying in the vacuum oven overnight at room temperature, afforded 5.46 g (55%) of poly(p-acetoxystyrene) (III). (Mn = 1.17 x 104, Mz = 2.06 x 104, polydispersity — 1.76 (gpc), Mn — 1.85 x 4). 

Solution Photolysis of Poly(p-acetoxystyrene) A 2.576 g sample of III was dissolved in 350 ml of acetonitrile and placed in a 500 ml Hanovia reactor equipped with a water-cooled quartz finger and 500 watt mercury arc lamp, condenser, nitrogen inlet and bubbler. The solution was irradiated for a total of... 

The precipitate was filtered, washed with additional methanol and dried overnight in the vacuum oven at 40°C to give 1.82 g of polymer (71% recovery). H-NMR spectral analysis of the product confirmed that it contained both p-acetoxystyrene and 2-hydroxy-5-vinylacetophenone repeating units in a molar ratio of 0.52 0.48. The polymer had M = 4.50 x 10, Mz — 3.62 x 5, polydispersity = 8.06 (gpc). The spectral data which is listed below corresponds to the product after 39.5 hrs. of irradiation. 

A reaction flask was charged with 2-ethyl-2-adamantyl methacrylate (0.24 mol), p-acetoxystyrene (0.56 mol), and isopropanol (279 g) and then heated to 75°C. This mixture was next treated with dimethyl-2,2 -azobis(2-methylpropionate) (0.048 mol) dissolved in isopropanol (22.11 g), stirred 20 minutes, and finally refluxed for... 

Xu et al. have investigated Tg of poly(acetoxystyrene-co-isobutylstyryl-POSS) (PAS-POSS) copolymers [175]. It was foimd that the presence of POSS at a relatively lower content actually reduces the dipole-dipole interactions of PAS molecules and plays an inert diluent role to decrease the self-association interactions of PAS molecules. The Tg of the PAS-POSS decreases with the increase of the POSS content (up to 1.47%) in the hybrid polymer (Fig. 5). 

Block copolymers with hydroxyl segments were prepared by various ways An example utilizes the copper-catalyzed sequential copolymerizations of nBA and 2-[(trimethylsilyl)oxy]ethyl acrylate by the macroinitiator method into B-31 to B-33. The copolymers were then hydrolyzed into amphiphilic forms by deprotection of the silyl groups.313 A direct chain-extension reaction of polystyrene and PMMA with HEMA also afforded similar block copolymers with hydroxyl segments (B-34 and B-35).241-243 In block polymer B-36, a hydroxy-functionalized acrylamide provides a hydrophilic segment.117 Block copolymers of styrene and p-acetoxystyrene (B-37 to B-39), prepared by iron... 

Flydroxyl-capped poly (ethylene-co-butylene), a so-called Kraton, was converted into a macroinitiator via esterification with 2-bromopropionyl chloride, and then employed for the block copolymerizations of styrene and />acetoxystyrene (B-116 and B-117).403 A similar method is utilized for B-l 18 to B-121 where the esterification is with 2-bromoisobutyroyl bromide.341 A commercially available polybutadiene is also employed for B-122 via a similar transformation into the chloroacetyl group.404... 

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