2-Substituted 3-ethynylquinoxalines can be rapidly synthesized in generally excellent yields by a consecutive four-component synthesis starting from electron-rich π-nucleophiles, oxalyl chloride, terminal alkynes, and 1,2-diaminoarenes. The title compounds are highly fluorescent with a pronounced emission solvatochromism. The photophysical properties and electronic structure were additionally corroborated by computations on the DFT level of theory.
One step back, two steps forward! Starting from diverse heterocycles, the title reaction furnishes ynediones under very mild conditions in a direct and preparatively simple one‐pot process. The key to avoiding decarbonylation is the CuI‐catalyzed Stephens–Castro alkynylation rather than the usually more efficient Sonogashira coupling. In addition, novel highly atom‐economical four‐component syntheses of various heterocycles can be achieved.
Professor Akira Suzuki zum 80. Geburtstag gewidmet Kupfervermittelte Reaktionen spielen seit über einem Jahrhundert eine herausragende Rolle in der organischen Chemie, was durch viele wichtige Transformationen und Namensreaktionen zum Ausdruck kommt. Tatsächlich kann man Ullmann-Reaktionen auch als Vorläufer der modernen Kreuzkupplungen betrachten. Jedoch wurden die kupfervermittelten Prozesse nahezu vollkommen durch die dramatische Entwicklung der Palladiumchemie in den Schatten gestellt. Im letzten Jahrzehnt tauchten aber wiederum viele bemerkenswerte kupferkatalysierte Prozesse auf, sodass man heute von einer Renaissance der Kupferkatalyse sprechen kann.
SummaryA novel one-pot four-component synthesis of pyrimidyl- and pyrazolylazulenes through the use of glyoxylation–decarbonylative alkynylation–cyclocondensation sequences starting from azulene or guaiazulene as substrates, gives rise to the formation of the target compounds in moderate to good yields.
A novel consecutive three-component synthesis of 3-(hetero)aryl-1H-pyrazoles via room temperature Sonogashira arylation of propynal diethylacetal used as a propargyl aldehyde synthetic equivalent has been disclosed. The final acetal cleavage-cyclocondensation with hydrazine hydrochloride at 80 °C rapidly furnishes the title compounds in a one-pot fashion.
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