Thieno -1,3-oxazin-4-ones pyrimidines

Oxo-4//-thieno[2,3-(/][l,3]oxazines (332), which are available from 2-aminothiophene-3-carboxylic acids by introduction of a one-carbon unit either from acetic anhydride or from ethyloxalyl chloride, react with amines to give thieno[2,3-d]pyrimidin-4(3/i)-ones (Scheme 94) (72JMC106,79JMC505). 

Thieno[2,3-d]pyrimidines can also be synthesized by cyclic transformations from other ring systems. Thieno[2,3-d]oxazin-4-ones 123 were transformed into 3-substituted thieno[2,3-d]pyrimidin-4-ones 19a-d by treat-... 

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. 

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