2,4,6-Trisubstituted pyrimidines, formation

After carbonylative alkynylation of aryl iodides 34 with terminal alkynes 4 and in the presence of carbon monoxide under ambient pressure the subsequent addition of an amidinium salt 32 gives rise to the formation of 2,4,6-trisubstituted pyrimidines 33 in the sense of a four-component reaction (Scheme 25) [143]. 

Pyridine can become involved in nucleophilic substitution when very reactive triflates are being synthesized. One approach to minimize this disadvantage is to replace it with ster-ically hindered bases, such as 2,6-di-r-butyl-4-methylpyridine, 2,4,6-trisubstituted pyrimidines, or nonnucleophilic aliphatic amines (usually N,(V-diisobutyl-2,4-dimethyl-3-pentylamine). No salt formation appears to take place under these conditions. The triflic anhydride seems to be the direct triflating agent and the base only neutralizes the triflic acid formed. Numerous alkyl triflates have been prepared in the literature by the above method. Some recent examples of triflates prepared from alcohols are illustrated in eqs 2 and 3. As an exception, 2,6-dinitrobenzyl alcohol does not react with Tf20 although similar sulfonyl esters could be prepared. ... 

A rapid synthesis of trisubstituted l,2,4-triazolo[4,3-b]pyridazines has been devised to give selective variation of the three substituents through combinations of silicon-directed anion formation, palladium-catalyzed couplings and SnAt displacements <00TL781>. The synthesis of new l,2,4-triazolo[l,5-a]pyrimidines <00M1435>, 1,2,3-triazolo[4,5-(f]... 

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