Thieno oxazines

The acetic anhydride-induced cyclodehydration of the symmetrical diamide 411, derived from the tetrahydro-benzothiophene / -amino ester 410 and diethyl malonate, afforded the thieno[2,3-r7 [h3]oxazine derivative 413 rather than the expected bis-oxazine 412 (Scheme 78). The reaction probably takes place through sequential cyclizations, in which the pyridine ring of 413 is produced by condensation of the exocyclic double bond of the enamine tautomeric form of the 1,3-oxazine moiety and the mixed anhydride formed by the carboxylic group and acetic anhydride <2003PS245>. 

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. 

In recent years, procedures were devised for the synthesis of thienopyrimidines using recyclization of derivatives of thieno[2,3-J]oxazinones (2002JCR(S)5, 2002MI2, 2002JCR(S)0149), thieno[3,2-<7]oxazines (1998P775), and pyrano[3,4-<7lpy-rimidines (1999P858). 

Dihydro-l,2-oxazine ring. Aq. 30%-H2O2-soln. added to a mixture of methyl 5-p-tolyl-5,6-dihydro-4H-thieno[2,3-c]pyrrole-2-carboxylate and formic acid, stirred 36 hrs. whereby the solid dissolves after 1-2 hrs. and an exothermic reaction ensues -> methyl 5-p-tolyl-4,5-dihydro-7H-thieno[3,2-d] [l,2]oxazine-2-carboxyl-ate. Y 74%. F. e. s. J. Feijen and H. Wynberg, R. 89, 639 (1970). 

NHC-catalysedreactions of nitrosoarenes with4-(2-aroylvinyl)furan-3-carbaldehydes, 4-(2-aroylvinyl)thiophene-3-carbaldehydes, or 2-(2-aroylvinyl)nicotinaldehydes have been reported to give furo[3,4-fin[l,2]oxazin-4-ones, thieno[3,4-d][l,2]oxazin-4-ones, or pyrido[3,2-fiG[l,2]oxazin-5-ones, respectively (Scheme 196). " ... 

Thiophene as the first ring named in a fused system is shortened to thieno. 2-Methyl-2//-thiazolo [4,5 -e] -1,2-oxazine... 

Scheme 22. Synthesis of substituted thieno[2,3-cf [l,3]oxazin-4-ones 65 [136],...

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