101161-85-7Relevant academic research and scientific papers
Inverse electron demand diels-alder reactions of 1,2,3-triazines: Pronounced substituent effects on reactivity and cycloaddition scope
Anderson, Erin D.,Boger, Dale L.
, p. 12285 - 12292 (2011/09/16)
A systematic study of the inverse electron demand Diels-Alder reactions of 1,2,3-triazines is disclosed, including an examination of the impact of a C5 substituent. Such substituents were found to exhibit a remarkable impact on the cycloaddition reactivity of the 1,2,3-triazine without altering, and perhaps even enhancing, the intrinsic cycloaddition regioselectivity. The study revealed not only that the reactivity may be predictably modulated by a C5 substituent (R = CO2Me > Ph > H) but also that the impact is of a magnitude to convert 1,2,3-triazine (1) and its modest cycloaddition scope into a heterocyclic azadiene system with a reaction scope that portends extensive synthetic utility, expanding the range of participating dienophiles. Significantly, the studies define a now powerful additional heterocyclic azadiene, complementary to the isomeric 1,2,4-triazines and 1,3,5-triazines, capable of dependable participation in inverse electron demand Diels-Alder reactions, extending the number of complementary heterocyclic ring systems accessible with implementation of the methodology.
Intramolecular Diels-Alder Reactions of 1,2,4-Triazines. Synthesis of 2,3-Cyclopentenopyridines and 5,6,7,8-Tetrahydroquinolines
Taylor, Edward C.,Macor, John E.,French, Larry G.
, p. 1807 - 1812 (2007/10/02)
2,3-Cyclopentenopyridines and 5,6,7,8-tetrahydroquinolines are prepared by intramolecular Diels-Alder reactions of appropriately substituted 1,2,4-triazines.Two general routes to the requisite triazine precursors are described.
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.
Ammonia-induced Cyclization of Vinamidinium Systems
Jeyashri, B.,Balasubrahmanyam, S. N.
, p. 341 - 349 (2007/10/02)
In the course of adapting known reactions of vinamidinium (aminoiminopropenium) systems for preparing certain 2,3-cycloalkenopyridines bearing aryl substituents in the hetero ring, the concomitant formation of 3,5-diarylpyridines (A) is noticed.It has been confirmed that products A arise from a direct reaction of ammonia with 3-aryl-1,1,5,5-tetramethyl-1,5-diazapentadienium salts (B), the vinamidiniums taken.In the mechanism envisaged this direct reaction is thought to be initiated by the displacement of a dimethylamino group in B by ammonia.The formed species undergo branched dimerization, eventually yielding dienes for which both concerted and stepwise pathways are available for forming C5-N cyclates which can aromatize to yield A.Features of this mechanism, postulated for species B which are C-2 substituted propeniums, are compared with those of mechanisms considered as operative in cases of C-1 substituted ethenyl systems known to yield pyridines of structures similar to A on reaction with ammonia.The vantage provided by the apparent generality of these features has enabled an explanation for variation of product composition from exclusively a 3-acetylpyridine to exclusively 2-acetylaniline through a mixture thereof when the nitrogen atom of the monoenamine of acetylacetone is progressively alkylated and made to undergo cyclizing reactions.
