2H-1,4-Benzoxazin

A. Horti, D.E. Redmond, R. Soufer, No-carrier-added (nca) synthesis of 6-[F-18] fluoro-L-DOPA using 3,5,7,8,8a-hexahydro-7,7,8a-trimethyl-[6S-(6-alpha, 8-alpha, 8-alpha-beta]-6,8-methano-2H-1,4-benzoxazin-2-one, J. Label. Compds Radiopharm. 36 (1995) 409 23. 

H- 1,4-Benzoxazines (241) are available by the cyclization of acetals (240 X = 0) in acid solution (79M257). Similarly the reduction of 2-nitrophenoxyacetophenones (242) with zinc dust and ammonia affords the corresponding JV-oxide derivatives (243) (79T1771). 

Nair 482 reacted benzoxazole with a molar quantity of DM AD at room temperature for 10 days, then he heated the product for 6 hours at 100°, and obtained 3-methoxycarbonylmethylene-2-oxo-3,4-dihydro-2H-1,4-benzoxazine (18), identical with that obtained from o-amino-phenol and the acetylenic ester his benzoxazole may have hydrolyzed before or during reaction. 

Considerable effort has been made by us to detect the supposed precursor of 4-acetyl-BOA (4-ABOA) in plants of the Canadian maize variety Funks G 4106 from kernels of which it was isolated22 and shown to be bioactive.51 52 Though we eventually succeeded in the synthesis of the supposed corresponding 5-acetyl-2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one, which indeed rapidly decomposed to form 4-ABOA in solution,21 we were unable to detect this aglucone or its glucoside in juvenile plant material. 

Atkinson, J., Morand, P., Arnason, J. T., Niemeyer, H. M. and Bravo, H. R. 1991. Analogues of the cyclic hydroxamic acid 2,4-dihydroxy-2H-1,4-benzoxazin-3-one decomposition to benzoxazolinones and reaction with -mercaptoethanol. J. Org. Chem. 56, 1788-1800... 

Grambow, H. J., Luckge, A., Klausener, E., and Muller, Z. 1986. Occurrence of 2-(2-Hydroxy-4,-7-dimethoxy-2H-1,4-benzoxazin-3-one)-P-D-glucopyra-... 

Hartenstein, H., Klein, J. and Sicker, D. 1993. Efficient isolation procedure for (2R)-2-P-D-Glucopyranosyloxy-4-hydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one from maize. Ind. J. Heterocycl. Chem. 2, 151-153... 

Sicker, D. and Hartenstein, H. 1993. A new general approach to the 2-hydroxy-2H-1,4-benzoxazin-3(4H)-one skeleton via diisobutylaluminum hydride reduction of 2,3-dioxo-1,4-benzoxazines. Synthesis, 771-772... 

Thunecke, F., Hartenstein, H., Sicker, D., and Vogt, C. 1994. Separation of enantiomers and diastereomers of 4-hydroxy-2H-1,4-benzoxazin-3(4H)-one derivatives by capillary electrophoresis. Chromatographia 38, 470-474... 

Azine approach. Heteroaromatic TV-oxides will undergo 1,3-dipolar cycloaddition as a nitrone. Thus quinoxaline 1-oxide reacts with a variety of dipolarophiles, e.g. in the formation of the adduct (85). The 1,4-dioxide can form cycloadducts at both N-oxide functions. The adduct from 2H-1,4-benzoxazine 4-oxide and acrylonitrile is the isoxazolo[3,2-c][l,4]benzoxazine (86) (79T1771). 

Benzoxazol 2-Hydrazinocarbo-nyl- E8a, 1138 (3-C1 —2-oxo — 2H-1,4-benzoxazin + N2H4) Essigsaure, Azido-phenyl- E21e, 5135 (CO-NR2 COOH)... 

Similarly, nucleophilic substitution by thiourea of 2-bromo-4-hydroxy-2H-1,4-benzoxazin-3 (4//)-one, and 2-bromo-4-hydroxy-2/f-1,4-benzo-thiazin-3(4//)-one, gave rise to S-[4-hydroxy-2//-l,4-benzoxazin-3(4i )-on-2-yl]-isothiouronium bromide and S-[4-hydroxy-2fiM,4-benzothiazin-3(4/i/)-on-2-yl]-isothiouronium bromide, respectively. On alkaline cleavage the four isothiouronium bromides showed a different behaviour. 

The 2-amino and 2-mercapto derivatives of the 2H-1,4-benzoxazin-3(4/f)-one and 2H-1,4-benzothiazin-3 (4//)-one skeletons have not yet been described. We prepared them from the starting 2-bromo-2//-l,4-benzoxazin-3(4//)-one and 2-bromo-2//-l,4-benzothiazin-3(4//)-one, respectively [126] (Fig. (16)). 

Schema 51. Die Biosynthese des Tryptophans und des 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-on...

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