Dihydro-4H-1,3-oxazines

As pointed out previously (Section II,B,l,e), 2-amino-5,6-dihydro-4H- 1,3-oxazines are tautomeric with 2-imino-tetrahydro-1,3-oxazines125 [Eq. (23)]. 

Addition to the side-chain of the aldimine from 4-anisaldehyde and aniline occurred in its reaction with the furan-2,3-dione shown with toss of carbon monoxide by heating in benzene during 2 hours to give 2-(4-methoxy-phenyl)-3,6-diphenyl-2,3-dihydro-4H-1,3-oxazine-4-one in 93% yield (ref.131)... 

C1bH1eBrNO, 2-Phenyl-4-(4-bromophenyl)-5,6-dimethyl-5,6-dihydro-4H-1,3-oxazine, 39B, 262... 

Benzyl-4,4,6-trimethyl-5,6-dihydro-4H-1,3-oxazine dissolved in tetrahydro-furan-ethanol (1 1), 9 N HGl added to pH 7, then aq. NaBH4 added at -30° with simultaneous addition of more HGl to keep the pH at 7, and stirred 1 hr. at -30° after the addition 2-benzyl-4,4,6-trimethyltetrahydro-l,3-oxazine. Y 88%. - Via this reduction, aldehydes, inch deuterioaldehydes, can be prepared from carboxylic acids and nitriles. F. e. s. A. I. Meyers and A. Nabeya, Ghem. Gommun. 1967, 1163. 

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