A practical synthesis of new S,N-disubstituted derivatives of 5-(4-methylpiperidino)methyl-2-thiouracil

5-(4-Methylpiperidino)methyl-2-thiouracil (1) has been obtained via the Mannich reaction between 2-thiouracil, paraformaldehyde, and a cyclic secondary amine such as 4-methylpiperidine (4-MP) in ethanol. New S,N(1)-di-o-(m- and p-)bromo-(nitro-) benzyl-substituted derivatives have been synthesized successfully in the reactions of 1 with the corresponding o-(m- and p-)bromobenzyl bromides or o-(m- and p-) nitrobenzyl chlorides in DMF solution in the presence of K2CO3. The opposite method of synthesis, that is, the reaction between 2-o-(m- and p-)bromobenzylthio-1-o-(m- and p-)bromobenzyluracils and 2-o-(m- and p-)nitrobenzylthio-1-o-(m- and p-) nitrobenzyluracils (8), with paraformaldehyde and 4-methylpiperidine in ethanol failed, indicating the important role of the enol form of 2-thiouracil for the Mannich reaction to be successful.