Pyrimidine reactions. VIII. Methiodides formed from some dimethylaminopyrimidines

4.Dimethylaminopyrimidine and its 2-chloro-, 2-dimethylamino-, 6-chloro-, 6-methylthio-, and 6-dimethylamino-derivatives are quaternized by methyl iodide at N 1. The structures of the resulting methiodides are proven by alkaline degradation to known oxopyrimidines. 4-Dimethylamino-2-(and 6-)methoxypyrimidine and 2-dimethylamino-4-methoxypyrimidine all undergo quaternization on a nuclear nitrogen atom followed by spontaneous loss of methyl iodide to yield oxopyrimidines (cf. the so-called Johnson and Hilbert nucleoside synthesis). The unique lability of the dimethylamino group in these quaternary compounds is exemplified in the con- version of 2-dimethylamino-1,6-dihydro-1,3-dimethyl-6-oxopyrimidinium iodide into 1,3-dimethyluracil by mere dissolution in water or aqueous ethanol, and by the reaction of 2,4-bisdimethylamino-I-methylpyrimidinium iodide with ethanolic sodium hydrogen sulphide to give 4-dimethylamino-1,2-dihydro-1-methyl-2-thio- pyrimidine.