Oxazolo pyrimidinone

The reaction of 3-aminopyridopyrimidin-4-one 330 with acetone in boiling dichloromethane in the presence of a catalytic amount of acetic acid for 5 hours followed by 24-hour stirring at room temperature or with 37% aqueous formalin in boiling ethanol for 2 hours afforded tricyclic oxazolo[5,4-c/]pyrido[l,2-a]pyrimidinones 462 [91IJC(B)839]. 

N-Alkylation in the azine ring is demonstrated by the preparation of 2-substituted 6-(jS-D-ribofuranosyl)oxazolo[5,4-rf]pyrimidin-7(6/T)-ones (181). In this case the silyl ether variant of the Hilbert-Johnson method for the synthesis of pyrimidine nucleosides has been used the pyrimidinone (180) is converted into its silyl ether using HMDS and the ether reacted with 2,3,5-tri-O-acetyl-D-ribofuranosyl bromide under Hg(II) catalysis. Deacetylation using methanolic ammonia gives the nucleoside with a /3-anomeric configuration (74JMC1282). 

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