Pyrimidines, 1,2-dihydro-, synthesis from

Pyrimidine-4,6(lH,3H)-dione, 5-ethyl-2,5-dihydro-2,5-diphenyl-synthesis, 3, 108 Pyrimidine-2,4( 1 H,3H)-diones thiation, 3, 89 Pyrimidine-4,5-diones purine synthesis from, 5, 582 Pyrimidine-4,6-diones tautomerism, 2, 27... 

The preparation of 9-niethyl and 9-butyl-2-hydroxy-8,9-dihydro-7H-purine-8-thione (XXVa Table 7) is somewhat unusual. Brown [45) has obtained these compounds from carbon disulfide and respectively f-methyl and 1 -butyl-5,6-diamino-1,2-dihydropyrimidin-2-one (XXIVa.). Evidently a shift of the alkyl group from the 3-N to the 9 N atom must occur during the ring closure. The structure of these two purines has been confirmed by their independent synthesis from 4-methylamino and 4-butylamino-5-amino-2-hydroxy pyrimidine. 

Reaction of pyridines with dialkyl acetylenedicarboxylates in the presence of isocyanates in dry CH2C12 at room temperature produced 1-substituted 2-oxo-l,9a-dihydro-2/7-pyrido[l,2-tf]pyrimidine-3,4-dicarboxylates <2004TL1803>. One-pot, three-component synthesis of 1-substituted 2-oxo-l,llb-dihydro-2//-pyrimido[2,l- ]iso-quinoline-3,4-dicarboxylates and 4-(3-chloro-4-methylphenyl)-3-oxo-4,4a-dihydro-3/7-pyrimido[l,2-tf]quinoline-l,2-dicarboxylate was realized by the reaction of isoquinoline and quinoline with isocyanates and dialkyl acetylenedicarboxylates <2004S861>. Diastereomeric mixtures of l-tosyl-2-aryl-l,llb-dihydro-2/7-pyrimido[2,Ttf]isoquinoline-3,4-dicarboxylates were obtained from isoquinoline, iV-tosyl-benzaldehyde imines, and DMAD <2002OL3575>. 

Partly saturated pyrazino[l,2-r-]pyrimidines were prepared by formation of the pyrazine ring. 2-Substituted-8-hydroxy-3,4-dihydro-177,277-pyrazino[l,2-r-]pyrimidin-l-ones were prepared by a [6+0] synthesis involving cyclization of 6-hydroxy-pyrimidine-4-(fV-hydroxyethyl)carboxamides <2005W02005/087766>. The 2/7-pyra-zino[l,2-c]pyrimidine-3-carboxamide 164 (Y = NH) was formed from [5+1] atom fragments via the uracil derivative 163 (Y = NH) and DMF-dimethyl acetal. Compounds 163 were prepared from 6-chloromethyluracil and glycine methyl ester 162 (Y = NH) (Scheme 20) <2004W02004/014354>. 

The one-step synthesis of further tri- and tetracyclic pteridine derivatives from 2-aminopyrazine 153 has also been described <2001JHC1173>. Cyclic analogues of A -[bis(methylthio)methylene]amino reagents such as 2-(methylthio)-2-thiazoline, 5,6-dihydro-2-(methylthio)-4//-l,3-thiazine, 2-(methylthio)-2-imidazoline, 2-(methylthio)-l,4,5,6-tetrahydro-pyrimidine, 2-(methylthio)-2-pyrazine, and 2-chloropyrimidine reacted with aminopyrazine 153 to afford thiazolo/thia-zino[2,3-3]- 159 ( = 1 (53%), n = 2 (42%)), imidazo/pyrimidino[2,l-/ ]- 160 ( = 1 (53%), = 2 (57%)), pyrazino[2,l-/ ]-161 (21%), and pyrimido[2,l-/ ]-pteridine 162 (42%) derivatives, respectively. 

Azole approach. A one-pot synthesis of substituted 2,3-dihydro-5-oxo-5H-oxazolo[2,3-b ]quinazolines (273) consists of reacting esters of anthranilic acid with a 2-chloro- or 2-bromoalkyl-isocyanate the initially formed urea (271) is cyclized to the acid salt of the oxazoline (272), which on addition of piperidine as base forms the pyrimidine ring (76S469). In a similar reaction the aziridinyl urea (274), which is available from aziridinyl isocyanate... 

---