Pyrimidines 4-acylamino- from

Unsaturated pyrazino[l,2-tf]pyrimidines were synthesized by formation of two bonds from [3+3] atom fragments. The 3-carbethoxy- and 3-acylamino-pyrazino[l,2-tf]pyrimidin-4-ones 81 and 87 were prepared from the 2-aminopyrazines 78 and 84 as depicted in Schemes 9 and 10, respectively. The mesoionic 95 was prepared as shown in Equation (8). 

The H mode of the pyrimidine ring construction assuming the stepwise formation of the N(l)-C(2) and C(2)-N(3) bonds as a result of the insertion of a component serving as the source of the C(2) atom is more often used in practice. The simplest modification involves intramolecular condensation of 3-(acylamino)thienopyri-dines produced by acylation of 3-amino-2-carbamoylthieno[2,3-Z>]pyridines or their structural analogs (1995PS83). An example is the synthesis of pyrimidothienobenzo-quinoline 98 from chloroacetamide 99. 

A multistep preparation of a thieno[3,2-e]-l,4-diazepin-2(3//)-one (285) has been accomplished, starting from the thienooxazinone 284 obtained from methyl 3-acetylaminothiophene-3-carboxylate (283) and phosphorus pentachloride.154 Similarly, 3-methylthieno[2,3-d]pyrimidin-4-(3//)-ones (288) were obtained in an exothermic reaction by heating methyl 2-acylamino-3-thiophenecarboxylates (286) with N,AT-dimethylphosphordiamidate (287) up to 250°C155 (Scheme 78). Ethyl 2-acylamino-3-pyridinecarboxylate (289) gave, on heating with excess amine hydrochloride and phosphorus pentoxide/iV,AP-dimethylcyclohexylamine, a series of pyrido[2,3-d]pyrim-idine-4(3if)-ones (290).156... 

The synthesis of purines from monoacyl pyrimidine-4,5-diamines is a commonly used method (for example, [2252]). Similarly, 8-hydroxymethylpurin-6-one is synthesized from S-acylamino-6-aminopyrimidin-4-one and ethyl glycoiate but... 

Thieno[2,3- /]pyrimidines have been synthesized from 5-acylamino-2,3-dialkylthiophen-4-aldehydes. 2-Amino-3-cyano-thiophens have been transformed into the 2-cyanamino-3-cyano-thiophens and ring-closed to 4-aminothieno[2,3-Raney nickel to the 4-oxo-pyrimidine (263). ... 

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