Benzo-2,3-dihydro-1.3-oxazines

Oxo.2-r6-nitio-3.4.uiethylen[Pg.1123]

The compounds with one double bond are dihydro-1,3-oxazines, and the structures shown in Fig. 1 are possible. The conformations of dihydro-1,3-oxazine rings arc based on analogy with cyclohexcne and also on the conformational analysis of several benzo-1,3-oxazine derivatives. 

Information concerning the spectral characteristics of 1,3-oxazinium derivatives discussed above is scant. Systematic investigations have not been carried out. In work devoted to the synthesis of 5,6-dihydro-l,3-oxazinium, 1,3-oxazinium, and benzo-l,3-oxazinium salts, these products underwent deprotonation without identification or even isolation. Such articles contain only the spectra of the corresponding uncharged 1,3-oxazines. A few recent publications describe these salts as individual compounds. 

Dihydro-1,4-oxazines, -thiazines and their benzo derivatives 1012... 

Another interesting reaction of benzoxazines 114 (115) is the reductive opening of the oxazine ring with simultaneous dehydrogenation of the pyrazoline moiety [170]. This process is carried out in a KOH suspension of a mixture of dimethyl sulfoxide and dimethylformamide. For instance, this treatment involving 2,5-diary l-l,10b-dihydro-177-pyrazolo[l,5-c]benzo[e]-l,3-oxazines 116 leads to the formation of pyrazoles 117 (Scheme 2.32). Similar disproportionation reactions have also been described for some bezopiranes, for example, pyrazole derivative 118 [91, 170]. 

Oxo-2,3-dihydro-4H- benzo-1,4-oxazin) entsteht durch Reduktion der N- 2-Ni-tro-phenoxyacetyl)-amino-sauren in schwach alkalischem Milieu iiber Platin(IV)-oxid4 ... 

Dihydro-(benzo-l,4-oxazine) werden mit Eisen/Salzsaure aus -(2-Nitro-phenoxy)-alkoholen erhalten (s. Bd. VIM, S. 555, Tab. S. 559, 560). 

Die Umsetzung von 2,4-Dioxo-l,2-dihydro-4H- (Isatosaureanhy-drid) mit Natriumhydrogensulfid liefert unter Decarboxylierung Natrium-2-amino-thiobenzoat45 47 ... 

Thermal decarboxylation (at 150 °C) of 3-carboxy-5,6-dihydro-4/f-l,2-oxazines (376) proceeds with concomitant ring-opening to give y-hydroxy-nitriles (377) in excellent yields. 4-Aryl-benzo[ (][l,2]oxazin-l-ones (378) have been prepared by treatment of monosubstituted benzenes with N-hydroxyphthalimide under Friedel-Crafts conditions (AICI3, heat for 15 min) reaction occurs para to the substituent. ... 

Mandelaldehyde, PhCH(OH)CHO, can be condensed with 7V-phenyl-ethanolamine under acid catalysis to afford the 5,6-dihydro-1,4-oxazine (393) (80%) none of the isomeric oxazolidine is formed.""" Oxidation of isatins with peroxodisulphate gives excellent yields of 2,3-dioxo-benzo[Z>]-l,4-oxazines (394), in contrast to the formation of isatoic anhydrides by oxidation with a peroxide." Benzo[f>]-l,4-oxazines that are functionalized with methylene at position 2, i.e. (395), are obtained in good yields by the mercuric-oxide-promoted cyclization of o-(propargylamino)phenols." ... 

In an earlier report, Gabriele and co-workers used similar reaction conditions in the synthesis of 2,3-dihydrobenzo[l,4]dioxine and 3,4-dihydro-2ff-benzo[1.4]oxazine derivatives 170 from 2-prop-2-ynyloxyphenols and 2-prop-2-ynyloxyanilines, respectively (Scheme 79) (141). 

ChIor-2-hydrazino-8-oxo-2-phenyl-2.3-dihydro-[benzo-l. 2 4.5-(1.3-oxazin)] 27 II497. 

Oxo-2-[4-di thylamino. enyl]-3 aoetyl-3.6-dihydro-4.5-benzo-1.3-oxazin 2711480. 

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