Benzoxazole, 2-methyl

Benzoxazole, 2-carbonamidomethyl-5-methyl-, 1, 333 Benzoxazole, 2,3-dihydroring-chain tautomerism, 6, 186 structure, 6, 179 synthesis, 6, 227-228 Benzoxazole, 2-dimethylamino-synthesis, 5, 128 Benzoxazole, 2-mercapto-... 

Heating 2,3-dinitroaeetanlllde (5) with sodium ethoxide in DMF gave a mixture of 2-methyl-7-nitro-benzoxazole (6) and 2-nitro-6-aeetamidophenol (7) (Eq. 4). The latter is also formed under the same eonditions from 6. Consequently, the probable meehanism of the reaetion Involves primarily the denitroeyelization reaetion leading to 6, whleh is then partially hydrolyzed to 7 (80KGS417). 

Formation of the oxazole ring is not always the last step in synthesis of the brightener. Unsymmetrical compounds that contain both a benzoxazole group and an ethene linkage can be prepared by the anil synthesis [51], in which a compound possessing an activated methyl group reacts with a Schiff base. The preparation of brightener 11.31 is an illustration of this method (Scheme 11.12). 

In general, symmetrical oxo-squaraines having the same end-groups are synthesized by reacting squaric acid with two equivalents of quatemized indolenine, 2-methyl-substituted benzothiazole, benzoselenazole, pyridine, quinoline [39, 45, 46] (Fig. 4) in a mixture of 1-butanol - toluene or 1-butanol - benzene with azeotropic removal of water in presence [39, 45] or absence [47] of quinoline as a catalyst. Other reported solvent systems include 1-butanol - pyridine [48], 1-propanol - chlorobenzene, or a mixture of acetic acid with pyridine and acetic anhydride [49]. Low CH-acidic, heterocyclic compounds such as quatemized aryl-azoles and benzoxazole do not react, and the corresponding oxo-squaraines cannot be obtained using this method [23, 50]. 

Cashin, C. H., Dawson, W. and Kitchen, E.A. (1977). The pharmacology of benoxaprofen (2-[4-chlorophynl]-a-methyl-5-benzoxazole acetic acid), LRCL 3794, a new compound with anti-inflammatory activity apparently unrelated to inhibition of prostaglandin synthesis. J. Pharm. Pharmacol. 29 330-336. 

Auch die Herstellung von 3,4-Bis-[J, 2-benzoxazol-3-yl -furaza>i-2-oxid aus 3-(Carboxy-methyl)-1,2-benzoxazol mit Salpetersaure verlauft unter Decarboxylierung344. 

Erhitzt man 3-Azido-2-nitro-acetophenon, erhalt man nach Stickstoff-Abspaltung nicht das 4-Acetyl-benzofurazan-l-oxid (X), sondern 3-Methyl-7-nitro-2,l-benzoxazol (s. S. 788)272. 

HO h3c,J no2 L5s -xooh H11C6-N=C = N-C6H / (HsC2)20 h JU 0 3,7-Dioxo-6-methyl- 3,7-dihydro-2,I- benzoxazol-I-oxid E14b, 876 (1990)... 

The first step in the constmction of the terminal side chain in the first glitazones comprises a reaction of benzaldehyde (106-1) with the mono-oxime (106-2) from biacetyl to afford the benzoxazole Al-oxide (106-3). Reaction of that intermediate with phosphoms oxychloride leads the chlorination of the adjacent methyl group in a version of the Plonovski reaction to afford the choromethyl derivative (106-4). This is then used to alkylate the carbanion from the substimted acetoacetate... 

Fio. 1. Bronsted plot for azoles reacting with methylating agents in quaternization reactions. Pyridine is the reference substrate. 1, 1-methylimidazole 2, 1-methylbenzimidazole 3, thiazole 4, 1-methylpyrazole 5, 2-methylindazole 6, benzo-thiazole 7, oxazole 8, 1-methylindazole 9, benzoxazole 10, 2,1-benzisothiazole 11, isothiazole 12, 2,1-benzisoxazole 13, isoxazole and 14, 1,2-benzisoxazole. 

In the course of reduction experiments of methyl 12,14-dinitrodehydroabietate 3, a new benzoxazole resin add derivative 6 was synthesized and its structure established by spectroscopic data, chemical derivatization and X-ray analysis. 

This surprising reactivity of extremely weakly acidic methyl groups has resulted in extending the Anil Synthesis to a number of heterocyclic systems in which activation in the sense of the benzoxazole group would not be expected. 

Methyl-substituted thiophenes are also capable of reaction with benzalaniline, provided that the 5-position carries a carbo- or heterocyclic aromatic group, as, for example, 2-(benzoxazol-2-yl)-5-methyl-thiophene (109), which yields the styryl derivative 110.11 The isomeric compound 111 may be obtained analogously from 2-(/ -tolyl)benzox-azole and Schiff s base from 2-formylthiophene and p-chloroaniline. 

Nitrile oxides react with the methyl enol ethers of (Rs)-l -fluoro-alkyl-2-(p-tolylsulfinyl)ethanones to produce (45,5/f,/fs)-4,5-dihydroisoxazoles with high regio-and diastereo-selectivity.87 In the 1,3-dipolar cycloaddition of benzonitrile oxide with adamantane-2-thiones and 2-methyleneadamantanes, the favoured approach is syn, as predicted by the Cieplak s transition-state hyperconjugation model.88 The 1,3-dipolar cycloaddition reaction of acetonitrile oxide with bicyclo[2.2.l]hepta-2,5-diene yields two 1 1 adducts and four of six possible 2 1 adducts.89 Moderate catalytic efficiency, ligand acceleration effect, and concentration effect have been observed in the magnesium ion-mediated 1,3-dipolar cycloadditions of stable mesitonitrile oxide to allylic alcohols.90 The cycloaddition reactions of acryloyl derivatives of the Rebek imide benzoxazole with nitrile oxides are very stereoselective but show reaction rates and regioselectivities comparable to simple achiral models.91. 

The effects of a-, (3-, y-, and 2,6-di-o-methyl-(3-CDs on the ground- and excited-state properties of 2-(2 -hydroxyphenyl)benzoxazole (HBO), 2-(2 -hydrox-yphenyl)benzothiazole (HBT), and 2-(2 -hydroxyphenyl)benzimidazole (HBI) (42) in aqueous media have been investigated using fluorescence [184], The molecules form 1 1 complexes with a reasonably high association constant, and they enter the cavity axially from the wider-rim side of (3-CD with the benzazole... 

Whereas UL 94 delivers only a classification based on a pass-and-fail system, LOI can be used to rank and compare the flammability behavior of different materials. In Figure 15.2 the increasing LOI values are presented for different polymers as an example POM = poly(oxymethylene), PEO = poly(ethyl oxide), PMMA = poly(methyl methacrylate), PE = polyethylene), PP, ABS, PS, PET = polyethylene terephthalate), PVA = poly(vinyl alcohol), PBT, PA = poly(amide), PC, PPO = poly(phenylene oxide), PSU, PEEK = poly(ether ether ketone), PAEK = poly(aryl ether ketone), PES, PBI = poly(benzimidazole), PEI = poly(ether imide), PVC = poly(vinyl chloride), PBO = poly(aryl ether benzoxazole), PTFE. The higher the LOI, the better is the intrinsic flame retardancy. Apart from rigid PVC, nearly all commodity and technical polymers are flammable. Only a few high-performance polymers are self-extinguishing. Table 15.1 shows an example of how the LOI is used in the development of flame-retarded materials. The flame retardant red phosphorus (Pred) increases... 

Benzoin, IV, 87 Benzoquinone, oxime, IV, 101 —, phytochemical reduction of, IV, 89 o-Benzoquinone, tetrabromo-, IV, 89 p-Benzoquinone, tetrahydroxy-, III, 48 Benzoxazole, 5-acetamido-2-methyl-, III, 351... 

Phenylenediamine and 2-aminophenol initially give N-arylimidoyl fluoride. Elimination of hydrogen fluoride from the product and further intramolecular nucleophilic cyclization lead to perfluoroalkyl derivatives of benzimidazole and benzoxazole, respectively. In the case of 2-aminothio-phenol, the reaction occurs at the sulfur atom and forms a carbanion. If RF is fluorine, then the carbanion is destabilized by the interaction of the lone electron pairs of fluorine with the center, and the stabilization reactions occur with participation of the proton. If, however, RF is the trifluoro-methyl group, the negative charge is stabilized by it. The fluoride ion is eliminated with further intramolecular nucleophilic cyclization. 

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