61416-99-7Relevant articles and documents
1,3-Diaza-1,3-butadienes. Synthesis and conversion into pyrimidines by [4π + 2π] cycloaddition with electron deficient acetylenes. Synthetic utility of 2-(trichloromethyl)pyrimidines
Guzman,Romero,Talamas,Villena,Greenhouse,Muchowski
, p. 2470 - 2483 (2007/10/03)
Methods have been devised to generate 1H-1,3-diaza-1,3-butadienes bearing a leaving group at position-4 in latent, masked, and unprotected forms. A hallmark of these azadienes is that they undergo thermal [4π ± 2π] cycloaddition reactions with electron deficient acetylenes to give adducts which are aromatized to pyrimidine derivatives under the reaction conditions. Thus, 1-(methoxycarbonyl)-3-acylamidines 17 on heating in solution are converted in situ into the 1,3-diaza-1,3-dienes 18 and/or 19 which react with dimethyl acetylenedicarboxylate (DMAD) to produce the pyrimidines 26. The 1-Boc-1,3-diaza-1,3-dienes 24 are masked forms of the 1H-dienes inasmuch as they react with DMAD under relatively mild conditions to give the dihydropyrimidine adducts 25, which are easily detectable by 1H NMR spectroscopy, and which aromatize to pyrimidines 20 at higher temperatures. The 4-methylthio compounds 31 and 33, and the 2-(trichloromethyl) compounds 37, are isolable, relatively stable, 1H-1,3-diaza-1,3-butadienes. These easily prepared compounds react with electron deficient acetylenes under mild conditions to provide the pyrimidines 20, 34, and 38, respectively, in fair to excellent yields. The 2-(trichloromethyl)pyrimidines 38 are very useful precursors of a wide variety of other 2-substituted pyrimidines 46-52.
