2- Amino-5- -1,4-benzoquinone-3 carboxylic acid

Benzonitrile, 2,6-dimethoxy-, 22, 35 Benzophenone, 23, 99 Benzophenone azine, 24, 55 Benzophenone hydrazone, 24, 54 1,2-Benzopyran-3-carboxylic acid, 2-oxo-, ethyl ester, 28, 24 Benzopyrrole, 23, 42 Benzo(j) )quinolizine, 1,2,3,5,6,7-HEXAHYDRO-, 26, 40 -Benzoquinone, 26, 25 Benzothiazole, I-amino-5-methyl-, 22,16... 

The overall autoxidative pathway for HA is shown in Fig. (2). Note that the further autoxidation of the intermediate D and the successive cyclisation and aromatisation reactions leading to the substituted phenox-azinone CA 7 all show the features already pointed out for the autoxidation of HA to its quinonoid counterpart l-benzoquinone-2-imine-3-carboxylic acid C [17], CA is the main, albeit certainly not the only, product of HA autoxidation under a wide range of experimental conditions [17,34], At pH 7, significant amounts of another quinonisation product, 2- amino- 5- [(2 - carboxy- 6 - hydroxyphenyl)- amino]- 1,4-benzoquinone- 3- carboxylic acid, I in Fig. (4) were found. 

Further X-my and electron diffraction studies are reported. Analysis of 3-diazocamphor by X-ray diffraction shows some contribution of the enolate which provides a means of stabilization by charge delocalization. The observed C-1—C-7—C-4 angle of 92° agrees well with values obtained earlier by diffraction methods and by analysis of the n.m.r. spectrum of partly oriented nor-bornadiene. The 2-aminonorbornane-2-carboxylic acids show biological activity in inhibiting the Na -independent transport of non-polar amino-acids across cell membranes. The structure of 2-exo-aminonorbornane-2-carboxylic acid has been determined. The adduct of cyclopentadiene dimer with N-sulphinylaniline has structure (50). As (50) was obtained after several crystallizations it is probable that other isomers, which have not been reported, are present in the reaction mixture and the reaction is not fully regiospecific. The structure of the photoadduct of the butadiene-p-benzoquinone Diels-Alder adduct has been confirmed by a diffraction study as (51). 

The base-catalyzed cyclization of ethyl 3-[alkyl(4-cyanopyridazin-3-yl)amino]propanoates gives ethyl 8-alkyl-5-amino-7,8-dihydropyridazine-6-carboxylates 1, which by acidic hydrolysis were converted to the corresponding ends 2. Due to their air sensitivity, ends 2 are partly converted into ethyl 8-alkyl-5-oxo-5,8-dihydiopyiido[2,3-c]pyridazine-6-carboxylates 3. To avoid mixtures, the oxidation is completed by treatment with tetrachloro-l,2-benzoquinone (o-chloranil).20... 

Benzoquinone (1.71 g, 15.8 mmol) and 3.5 g ethyl 3-amino-3-(4-biphenylyl)-propenoate (9.8 mmol) in 50 mL acetic acid were refluxed for 1 h. After cooling, the crude product was precipitated out with light petroleum ether and Altered off, which was purified by column chromatography (EtOAc) and recrystallization (EtOAc) to yield 4.21 g ethyl 2-(4-biphenylyl)-5-hydroxyindole-3-carboxylate as a colorless solid, in a yield of 90%, m.p., 260-262°C. 

---