Oxazines and their Fused Derivatives

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.  

N-Methyl-tetrahydro-l,3-oxazine exists as a mixture of ring and open-chain tautomers in TFA the analogous oxazolidine behaves similarly. Of interest is the fact that ring-chain interconversion is more rapid for the oxazolidine, in converse to the predictions of Baldwin s vectorial rules. 

Salicylic acid, upon treatment with triphenylphosphine dithiocyanate, gives the benzo[ ]-l,3-oxazine (389) the cadmium-acetate-catalysed addition of N- p- 

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.  

Skvortsova, Z. V. Stepanova, and L. V. Andriyankova, Chem. Heterocycl. Compd. (Engl. Transi), 1979,15, 1036. 

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Oxazines and their Fused Derivatives.—Acid-catalysed rearrangement of the cyclopropyl ketoximes (371) affords 5,6-dihydro-4//-l,2-oxazines (372) (Scheme 143). ... 

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