2-Methylthio-6,7-dihydro-4//-pyrimido

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. 

USP3969506]. Reductive cyclization of 2-methylthio-l-(2-nitrobenzyl]-6-pyrimidines (515) with stannous chloride gave 6,1 l-dihydro-4//-pyrimido[2,l-fc]quinazolin-4-ones (516) (78JHC77). 

First representatives of the previously unknown tricyclic annulated system, viz., ethyl 7-methylthio-4,5-dihydro-3//-thieno[2,3,4-step synthesis from 4,6-dichloro-2-me-thylthiopyrimidine-5-carbonitrile (2000MI3). 

Cl3H13N3O3, Methyl 1,2,3,4-tetrahydro-1-methyl-2-oxo-pyrimido[1,2-a]benzimidazol-4-carboxylate, 4OB, 249 Cl3H14N4OS, 6,6-Dimethyl-3-methylthio-6,7-dihydro-as-triazino[1,6-c]quinazolin-5-ium-1-olate, 4IB, 343 Cl3H15NO2, trans-1 -Hydroxy-spiro[pyrrolidine-2,2 -tetralin]-5-one, 45B, 311... 

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