Benzoxazole 2-amino-6-nitro

In both syntheses the benzoxazole synthon 176 was prepared from methyl 5-hydroxyanthranilate (177), the amino group of which was trifluoroacetylated to give 178. Nitration of 178 gave the 6-nitro derivative 179 as the major product (in a 2 1 mixture with the 4-nitro compound) catalytic reduction to the 6-amino-5-hydroxy compound 180 was followed by refluxing with acetyl chloride in xylene to afford the benzoxazole 181, N-methylation of which yielded 176, the overall yield from 177 being 60% (94). 

It is interesting to note that 5-nitrobenzoxazole has two absorption maxima 224 (4.39) and 270 nm (3.84), while 6-nitrobenzoxazole shows only one maximum in area Amix 282 nm (4.01) [1200], A similar pattern is observed for 5-nitro- and 6-nitro-2-alkyl(aryl)benzoxazole too. The available experimental data are not enough to explain spectral differences of this kind. Apparently, it would be well to carry out quantum-chemical calculations or to involve other physical-chemical methods. An investigation of chromophoric 2-(4 -diphenyl)-5-nitrobenzoxazole with the help of UV (A 305 nm), fluorescence and laser spectroscopy has been reported by Chinese chemists [1201], Chromophores 2-(2 -hydroxy-4 -aminophenyl)-6-nitrobenzoxazole [ 1202], 2- [4-[4-(V,V-dihydroxyethyl-amino)-phenylazol]-phenyl -6-nitrobenzoxazole, 2-[4-(/V-mcthyl,V-hydroxyethyl-amino)... 

Benzimidazol-3-oxid 2-Cyan-5-nitro-E8c, 227 [(2,4-(N02)2—Ar] — NH — CH2— CN/Base 2,1-Benzoxazol 3-Amino-5-cyan-... 

Bei der Bildung der 2-Amino-benzamide aus 2-Nitro-benzonitrilen wird das Sauer-stoff-Atom vom intermediar-gebildeten N-Phenyl-hydroxylamin infolge voriibergehen-der Cyclisierung zum 3-Amino-l,2-benzoxazol auf die Cyan-Gruppe iibertragen1 2. 

The 1,3-dipolar cycloaddition reaction of non-stabilized azomethine ylides, derived from A-alkyl-cf-amino acids, with 3-nitro-2-trifluoro(trichloro)methyl-2//-chromenes produced l-benzopyrano[3,4-c]pyrrolidines in good yields." AgOAc-catalysed asymmetric 3 + 2-cycloaddition reactions of azomethine ylides with e-deficient alkenes yielded enr/o-adducts with up to 99% ee. New chiral ferrocenyl P,N-ligands possessing a benzoxazole ring as the Af-donor (35) are effective asymmetric catalysts... 

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