Oxazoles nitro

From Table 1, below, no signs of thermal decomposition were observed below 400 °C for nitrile and sulfonyl substituted di-and triaryl oxazoles. Nitro compounds, in contrast, exhibited marked thermal decomposition exotherms with decomposition onset temperatures of 360-365 °C, conditions only marginally compatible with polyimide curing conditions. Nitro aromatics are also oxidants which may lead to long-term stability problems. As a result of these experiments nitrile and sulfonyl substituted diaryl oxazoles were selected for polymer doping studies. 

In 1972, van Leusen, Hoogenboom and Siderius introduced the utility of TosMIC for the synthesis of azoles (pyrroles, oxazoles, imidazoles, thiazoles, etc.) by delivering a C-N-C fragment to polarized double bonds. In addition to the synthesis of 5-phenyloxazole, they also described reaction of TosMIC with /7-nitro- and /7-chloro-benzaldehyde (3) to provide analogous oxazoles 4 in 91% and 57% yield, respectively. Reaction of TosMIC with acid chlorides, anhydrides, or esters leads to oxazoles in which the tosyl group is retained. For example, reaction of acetic anhydride and TosMIC furnish oxazole 5 in 73% yield. ... 

Treatment of a 3-aminotriazolopyridine with acid gave the imidazopyridine 242 (81T1787), also obtained from the 3-nitro derivative by catalytic reduction (83AHC79). Quaternary salts derived from compound 2, when treated with tri-ethylamine and subsequently heated give 2-pyridylcyanamides 243 or 2-(oxazol-l-yl)pyridines 244 depending on the alkyl group (86H(24)2563) the ylides are presumably intermediates (see also Section IV.I). 

Nitro-bcnzaldehyd wird unter RingschluB zu Benzo-[c]-l,2-oxazol reduziert (Bd. X/l, S. 878). 

Nitro-benzophenon wird an Blei (geteilte Zelle, Athanol/Wasser/Natriumacetat) zu 3-Phenyl-(benzo-[c]-l,2-oxazol) (86% d.Th.) cyclisiert4 ... 

Auf ahnliche Weise erhalt man aus 2-Nitro-benzaldehyd in waBrig-alkoholischer Ace-tatpuffer-Losung Benzo-[c]-l,2-oxazol (51% d.Th.)1 ... 

In neutraler gepufferter Losung erhalt man aus l-Nitro-2-cyan-naphthalin 3-Atni-no- naphtho-[l, 2-c]-l, 2-oxazol)4 5 ... 

Bei —0,15 bis -0,4 V entsteht 3-Hydroxy-(naphtho-[ ,2-c]-oxazol) bzw. I-Hydr-oxy- (naphtho-[2,l-c]-l,2-oxazol) aus l-Nitro-2-aminocarbonyl- bzw. 2-Nitro-l-amino-carbonyl-naphthalin5 ... 

Analog reagieren 3-Nitro-2-aminocarbonyl- und 8-Nitro-l-aminocarbonyl (bzw. carboxy)-naphthalin5 zum 1 -Hydroxy-(naphtho-[2,3-c -1,2-oxazol) bzw. 8-Amino-naphthalin-1 -carbonsaure-lactam ... 

The base-catalysed reaction of a-bromo-a,P-unsaturated ketones with aliphatic nitro compounds leads to 2-isoxazoline A-oxides by tandem conjugate addition-ring closure (Scheme 5) <95JOC6624>. A -Acyl-3-isoxazolin-5-ones are transformed into oxazoles by photolysis or by flash vacuum pyrolysis (Scheme 6) <96TL675>. 

The synthesis of 3-H-oxazol-2-ones was described by Nam et al. [69]. The substituted benzoin 89 was formed from the coupling of 3,4,5-trimethoxy-benzaldehyde 18 with 3-nitro-4-methoxybenzaldehyde, Scheme 22. Reaction with PMB-isocyanate and subsequent cyclization gave the protected oxazolone derivative 90. The PMB group was removed by reflux in TFA and reduction of the nitro-group was performed using Zn to give the combretoxazolone-aniline 91. 

The electron impact mass spectra of 3-methyl-4-nitro-5-styryl-isoxazoles exhibit, on the contrary, only negligible loss of OH"80. This has been interpreted in terms of an isoxazole-to-azirine rearrangement80. The latter fragments directly to an abundant cinnamoyl ion as well as rearranges to oxazole and an epoxide through an intramolecular oxidation of the ethylenic bond by the nitro group80 see Scheme 10. 

The meso-ionic 1,3-oxazol-S-ones show an incredible array of cycloaddition reactions. Reference has already been made to the cycloaddition reactions of the derivative 50, which are interpreted as involving cycloaddition to the valence tautomer 51. In addition, an extremely comprehensive study of the 1,3-dipolar cycloaddition reactions of meso-ionic l,3-oxazol-5-ones (66) has been undertaken by Huisgen and his co-workers. The 1,3-dipolarophiles that have been examined include alkenes, alkynes, aldehydes, a-keto esters, a-diketones, thiobenzophenone, thiono esters, carbon oxysulfide, carbon disulfide, nitriles, nitro-, nitroso-, and azo-compounds, and cyclopropane and cyclobutene derivatives. In these reactions the l,3-oxazol-5-ones (66)... 

Of the many substituted and functionalized alkenes that have been combined with diazo dipoles to give A -pyrazolines or products derived from them (i.e., A -pyrazolines, pyrazoles, cyclopropanes), only a selection will be mentioned. These include ot-alkylidene-cycloalkanones (62), -flavanones, -thioflavanones, -chroma-nones, and thiochromanones (63,64) a-arylidene-indanones and -indolones (65) diarylideneacetones (66) l-benzopyran-2(77)-ones (coumarins) (67,68) 4-nitro-1,2-oxazoles (69) 2-alkylidene-2-cyanoacetates (70) dimethyl 2,3-dicyanofuma-rate (71) tetracyanoethylene (72) tetraethyl ethylenetetracarboxylate (72) 1,4-quinones (35,73-75) 2-X-l,l,l-trifluoro-2-propene [X = Br, (76), SPh, SOPh, S02Ph (77)] nitroalkenes (78) including sugar nitroalkenes (79) 1-diethoxyphos-phoryl-1-alkenyl-sulfoxides (80) methyl 2-(acetylamino)cinnamate and -acrylate... 

Nitro-2-phenyloxazole 271a undergoes Diels-Alder [4 + 2] cycloaddition with both electron-rich and electron-poor dienophiles to give an oxazoline 273 that may not be isolable due to the facile aromatization to a fused oxazole 274. Examples are shown in Table 8.22 (Scheme 8.77). 

Aus 4(5)-Nitro-imidazol erhalt man mit 2-Methyl-4,5-dihydro-oxazol unter Saurekatalyse... 

In Gegenwart von 2-Amino-1-nitro-1 -alkenen liefern 3,4-Diacyl-furazan-2-oxide bei der Ther-molyseuber 3-Acyl-5-dimethylamino-4-nitro-4,5-dihydro-l,2-oxazole unter Abspal-tung von Dimethylamin 3-Acyl-4-nitro-l,2-oxazole455 ... 

Aryl-4,5-dihydro-l,2-oxazole aligemeine Arbeitsvorschrift2 0,02 mol (/ )-l-Nitro-l-alken in 20 m/ trockenem Ether werden tropfenweise unter starkem Riihren zu einer Losung von 0,01 mol Benzonitril-oxid in 80 ml trockenem Ether bei 0° gegeben. Nach 12 h Riihren bei 25° wird die Mischung 2 h zum RiickfluB erhitzt, i.Vak. eingeengt und dcr Riickstand i.Vak. destilliert oder umkristallisiert. 

Telranitro-ethen addiert Ethen nach cinem Diradikal-Mechanismus zu 3-Nitro-4,5-dihydro-l,2-oxazol (32%)2 ... 

Mit Propen wird ein Gemisch aus 5-Methyl-3-nitro- und 4-Methyl-3-nitro-4,5-dihydro-l,2-oxazol (95 5 12%) und mit Ethenyl-trimethyl-silan 3-Nitro-5-trimethylsilyt-4,5-dihydro-1,2-oxazol (20%)2 erhalten. 

Nitriloxide konnen auch durch Umwandlung von primaren Nitro-aliphaten mit Chlor-ameisensaure-ethylester (Methode (a)) bzw. mit Benzol- oder Methansulfonsaure-chlorid (Methode ) in Gegenwart von Triethylamin und anschlieBender 1,3-dipolarer Cycloaddition mit Allyl-aryl-ethern in 5-Aryloxymethyl-4,5-dihydro-l, 2-oxazole iiberge-fiihrt werden2 ... 

Eulite (Eulyt, in Ger) or 5-Methyt-4-nitro-3 (l,1.dinitroethyl) i oxazole, Beil name 4-Nitro-5-methyl-3 [a,0-diniuoathyli-isoxazoI. Called by Quilico et al y-Metbyl-a-isoxazole-1 -d ini tTO 2-dinitToe thane,... 

Nucleophilic aromatic substitutions 1,3-azoles are more reactive than pyrrole, furan or thiaphene towards nucleophilic attack. Some examples of nucleophilic aromatic substitutions of oxazole, imidazole and thiazoles and their derivatives are given below. In the reaction with imidazole, the presence of a nitro-group in the reactant can activate the reaction because the nitro-group can act as an electron acceptor. 

Methyl-4-[3-iodo-5-nitro-(4-methoxy-phenoxy)-benzylidene]-4-H-oxazol-5-one... 

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