Study of Reaction between Activated Acetylenes and N,N′-Diethyl-2-thiobarbituric Acid in the Presence of Isocyanides or Triphenylphosphine

In a series of separate experiments reaction between N,N'-diethyl-2-thiobarbituric acid and acetylenic diesters in the presence of isocyanides or triphenylphosphine led to highly functionalized 4H-pyrano[2,3-d]thiopyrimidine or 1,4-di-ionic organophosphorus derivatives. The H-1 NMR spectra of diethyl-7-(2,6-dimethylphenylamino)-4-oxo-2-thio-1,3-diethyl-4H-pyrano[2,3-d]pyrimidine-5,6-dicarboxylate showed dynamic NMR effect that was attributed to restricted rotation around the aryl-nitrogen single bond. Activation free energy (Delta G(not equal)) for this process is about 54.85 +/- 2 kJ mol(-1) Betaines as 1,4-diionic organophosphorus compounds in this reaction are possessed of two vicinal stereo genic centers and exist in the solution as a mixture of two diastereoisomers. (C) 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:228-235, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20601