Synthesis of pyrimidines from β-dicarbonyl compounds and cyanogen: A metal-catalysed one-pot process

Highly functionalized pyrimidines can be prepared in good yields, by a one-pot procedure, from cyanogen and β-dicarbonyl compounds at ambient conditions in dichloroethane in the presence of catalytic amounts of Ni(acac)2 or Cu(acac)2. The pyrimidines obtained were fully characterized by a variety of physicochemical methods. The presence of at least one keto group in the substrate appears to be a necessary condition for the success of the synthesis, which fails, for instance, for dimethyl malonate. A kinetic study on the synthesis of 2-(1-amino-2-acetylbut-1-enonyl)-4- carboxamido-5-acetyl-6-methyl-1,3-diazine has been carried out by employing Cu(acac)2 as catalyst. A crucial step in the catalytic process is an insertion reaction of C2N2 into the C-H methine bond of a metal-co-ordinated 3-cyanoiminomethylpentane-2,4-dionato ligand, which leads to the formation of a carbon-carbon bond. This process characterizes this new pyrimidine synthesis, in that, as a rule, previously known ring-closure reactions implied only carbon-nitrogen bond formation. The simple addition product of C2N2 to acetyl-acetone, 3- cyanoiminomethylpentane-2,4-dione, is found to play an important kinetic role and its reaction with the organometallic ring mentioned above is a second critical process for the success of the ring closure.