114880-30-7Relevant articles and documents
Pyrazine- and pyridine-substituted prop-2-yn-1-ols, but-3-yn-2-ols, and but-3-yn-2-ones –purification, stability, and handling revised
Schindler, Claudia,Schulzke, Carola
, p. 1008 - 1013 (2015)
A short series of alkynyl-substituted pyrazine and pyridine derivatives was synthesized by the palladium-catalyzed Sonogashira cross-coupling reactions between aryl halides and alkynes. All the products are either white solids or colorless liquids, which is partly in contrast to previous reports. After purification, a color change or intense darkening was observed, in some cases starting almost immediately. Both, the nature of the heteroaromatic ring and the substituents of the alkyne moiety affect their stability. Herein details of synthesis, characterization, and, most importantly, purification and handling are reported.
Activating Pyrimidines by Pre-distortion for the General Synthesis of 7-Aza-indazoles from 2-Hydrazonylpyrimidines via Intramolecular Diels-Alder Reactions
Le Fouler, Vincent,Chen, Yu,Gandon, Vincent,Bizet, Vincent,Salomé, Christophe,Fessard, Thomas,Liu, Fang,Houk,Blanchard, Nicolas
supporting information, p. 15901 - 15909 (2019/10/22)
Pyrimidines are almost unreactive partners in Diels-Alder cycloadditions with alkenes and alkynes, and only reactions under drastic conditions have previously been reported. We describe how 2-hydrazonylpyrimidines, easily obtained in two steps from commercially available 2-halopyrimidines, can be exceptionally activated by trifluoroacetylation. This allows a Diels-Alder cycloaddition under very mild reaction conditions, leading to a large diversity of aza-indazoles, a ubiquitous scaffold in medicinal chemistry. This reaction is general and scalable and has an excellent functional group tolerance. A straightforward synthesis of a key intermediate of Bayer's Vericiguat illustrates the potential of this cycloaddition strategy. Quantum mechanical calculations show how the simple N-trifluoroacetylation of 2-hydrazonylpyrimidines distorts the substrate into a transition-state-like geometry that readily undergoes the intramolecular Diels-Alder cycloaddition.
