3 oxazin-1 -one

The reactions of isoxazolin-5-ones (1379) with 1 mol of phosphoryl chloride and DMF in boiling chloroform for 1.5 hr afforded 1,3-oxazin-6-ones (1381) in 69-74% yields via aminomethylenemalonate derivatives (1380) (87JOC3426). If 2 mols of Vilsmeier-Haack reagent were used in boiling carbon tetrachloride for 2 hr, then 1381 (R = H) and the amino-methylenemalonamate derivative (1382) were obtained in 8% and 76% yields, respectively, from 1379 (R = H). 

From reaction mixtures of isoquinolinium ylides (164, R = H, COOEt, COPh), and diphenylcyclopropenone in benzene, the pyridazino[6,l-a]iso-quinolines 49,50,55, and 63 were isolated in 10-33% yields, including 1,3-oxazine-6-ones (83JOC1084). Pyridazino[6,l-a]isoquinolin-2-one (63) was isomerized into the 2-hydroxy derivative 56. The reactions of isoquinolinium ylides (164, R = COOEt, COPh) with W-tosyldiphenylcyclopropenimine led to 4//-pyridazino[6,l-a]isoquinolines 42 and 54. 

It is well known that l,3-thiazine-4,6-diones can exist in three tautomeric forms <1960CB671, 1976KGS1042>. Cycloaddition of chlorocarbonyl ketenes with thioamides has been reported to produce only the 4-hydroxy-l,3-thiazin-6-ones, whereas the same reaction with amides gives either 4-hydroxy-1,3-oxazin-6-ones or a mixture of tautomers depending on the substituents on the starting materials <2005ARK(xv)88>. 

According to Sasaki et al.,212 diphenylcyclopropenone reacts with A-iminopyridinium ylids on refluxing in benzene to produce 2,4,5-trisubstituted-6//-1,3-oxazine-6-one (69) [Eq. (54)]. Matsukubo and Kato213 described the reaction of diphenylcyclopropenone and benzo-nitrile oxide through a hypothetical spiro intermediate to give 69 (R = Ph) in 40% yield [Eq. (55)]. 

Another interesting formation of 6H-1,3-oxazin-6-one derivatives by the oxidation of pyrrole derivatives was described by Sprio215 [Eq. (57)] (see also Yee et a/.216). 

H-1,3-Oxazin-6-one (68) is readily hydrolyzed to an open-chain product. It is isomerized by UV irradiation to the bicycle with fused four-membered rings (100), which on heating reverted to 68.210,211 Prolonged irradiation decomposed the substance into hydrogen cyanide, carbon dioxide, and acetylene.211... 

S,5R)-2-tert-butoxy-4-phenyl-5-(1 -ethoxyethoxy)-4,5-dihydro-1,3-oxazin-6-one (XXII)... 

Oxazine-6-ones as intermediates in synthesis of heterocycles 86G361. 

The optical rotatory dispersion (ORD) curves of the diastereomers of l-(p-nitrophenyl)-3-methylperhydropyrido[l,2-c][l,3]oxazines, obtained from (-)-2-(2-hydroxypropyl)piperidine with p-nitrobenzaldehyde, are nearly mirror images of each other (68CJC1105). The absolute configurations in cyclohexane of the dextrorotatory cw-3,4fl-H-3-phenyl- and trans-3,4fl-H-3-phenylhydropyrido[l, 2-c] [1,3]oxazin-6-ones, containing 3S,AaR and 35,4a5 atoms, respectively, were determined on the basis of the presence of positive Cotton effects (85T2891). 

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