1.3- Oxazin-6-ones reaction with amines

Reaction of the pyrido[2,3- [l,3]oxazin-4-one 215 with hydrazines and various primary amines in boiling ethanol yielded the corresponding 2-acetylaminopyridine derivatives 216 (Equation 17) <1994H(38)57>. 

Mesoionic pyrido[2,l- >][1,3]oxazines (54) afforded 4-oxo-4//-pyrido[l,2-a]pyrimidin-l-iumolates (55) and 4//-quinolizin-4-one (56) with phenyl iso(thio)cyanates [78LA1655 79CB1585 82ZN(B)222] and dimethyl acetylenedicarboxylate (79CB1585), respectively. Reaction of 2-cyano-3-methyl-lH,6//-pyridol[l,2-a][3,l]benzoxazine-l,6-dione with ammonium acetate and hydroxylamine, hydrazines, primary aliphatic or aromatic amines, and (thio)ureas gave 5-unsubstituted and 5-substituted 2-cyano-3-methyl-l//,6H-pyrido[l,2-a]quinazoline-l,6-diones (93CCC1953). 

One remarkable process is the photochemical synthesis of 3,4-dihydro-2H-l,3-oxazin-4-ones from a-sulfonyloxy-(3-keto amides (obtained by coupling of P-keto-carboxylic acids with amines, followed by treatment with an iodanyl mesylate). This allows the regioselective oxidation of less-activated C—H bonds and a C—O bond formation which is unusual for a Norrish-Yang reaction [69]. The formation of a 1,6-0—C biradical has been postulated as an intermediate (Scheme 9.42). 

A variety of amines, both aliphatic and aromatic, as well as ammonia, hydroxylamine, and hydrazine give an immediate reaction with 2-methyl- or 2-phenylpyrido[3,2-rf][l,3]oxazin-4-one. In the 2-phenyl series, the product is invariably a benzamidopyridine-2-carboxamide, whose cyclization to the pyrido[3,2-rf]pyrimidine is effected by dissolution in phosphoryl chloride424 (see Section 7.2.2.2.1.1.1.). 

Briel et al. (90GEP282011) describe the transformation of thieno[3,2-d]-l,3-oxazin-4-ones 361 into thieno[3,4-d]pyrimidines 362 by heating with ammonia saturated DMF or with primary amines. This transformation is an example of an ANRORC reaction. 

In a similar way, 2-oxazolidinones and tetrahydro-2//-l, 3-oxazin-2-ones have been prepared by the reaction of primary allyl amines and homoallyl amines10, respectively, with carbon dioxide and iodine in methanol via an intramolecular cyclization. Prolonged reaction for a week in the presence of cesium carbonate increases the yield to 70-90%. This reaction has a large applicability and the ease of the method makes it useful in organic synthesis. 

Pyridine-2-carboxamides may be prepared in a ring-opening reaction of 2-methyl- or 2-phenylpyrido[3,2-d][l,3]oxazin-4-one with various amines.424... 

Chloro-5-cyano-2-(WA -dimethylamino)-l,3-oxazin-6-one (264) is available through the reaction of the salts (263) of alkyl 2,2-dicyanoacetates and dichloromethyleninimium chloride. The chlorine atom of the oxazinone can be displaced by alkanols to give the alkoxy derivatives (265 R = O-alkyl). Similar treatment with primary and secondary amines yields the corresponding diamino-1,3-oxazinones (e.g. 265 R = Et2N, NHPh or NHBu) (Scheme 75) <905959). 

As base. Numerous reactions that are initiated by deprotonation have been conducted with KF-AI2O3. These include the synthesis of diaryl ethers, amines, and sulfides by nucleophilic aromatic substitutions, AJ-alkylation of 2,4-dinitrophenyl-hydrazones, condensation of 3-phenylisoxazol-5-one with aldehydes, and ring closure of /V-(w-chloroalkyl) carboxamides to afford 1,3-oxazolines and 1,3-oxazines. ... 

---