126215-89-2Relevant academic research and scientific papers
INTRAMOLECULAR DIELS-ALDER REACTIONS OF 2-(ALKYNYL)PYRIMIDINES AND 2-(ALKYNYL)PYRIDINES
Frissen, A. E.,Marcelis, A. T. M.,Geurtsen, G.,Bie, D. A. de,Plas, H. C. van der
, p. 5151 - 5162 (2007/10/02)
Pyrimidines 3,7 and 13 carrying an ο-alkynyl side-chain -CR2(CH2)nCH2CCH (R=H, CN; n=1,2) at the 2-position undergo intramolecular inverse electron demand Diels-Alder reactions across the C-2 and C-5 positions.Loss of hydrogen cyanide, caused by a retro-Diels-Alder reaction, from the intermediate cycloadducts leads to annelated pyridines 5,9 and 15, respectively.Similarly, from the nitropyridines 16 the 2,3-dihydronitro-1H-indenes 18 are obtained.The influence of electronic and steric effects on the rate of cycloaddition is discussed.Gem-disubstitution on the chain connecting the reaction centers leads to a considerable rate enhancement for compounds 3 vs 13.Compounds 7, having an extra methylene group in the tether between diene and dienophile, react much slower than compounds 3 due to decreased entropic assistance.
SUBSTITUENT EFFECTS IN THE INTRAMOLECULAR INVERSE ELECTRON DEMAND DIELS-ALDER REACTIONS OF 5-(P-SUBSTITUTED PHENYL)-2-(1,1-DICYANOPENT-4-YN-1-YL)PYRIMIDINES.
Frissen, A. E.,Marcelis, A. T. M.,Melger, W. C.,Plas, H. C. van der
, p. 6891 - 6900 (2007/10/02)
2-(1,1-dicyanopent-4-yn-1-yl)-5-phenylpyrimidines and some p-substituted phenyl derivatives undergo an intramolecular inverse electron demand Diels-Alder reaction to give the corresponding 3-aryl-7,7-dicyano-6,7-dihydro-5H-1-pyrindines.A Hammett plot of l
