BF₃-Mediated Acetylation of Pyrazolo[1,5-a]pyrimidines and Other π-Excedent (N-Hetero)arenes

Abstract

An operably simple microwave-assisted BF3-mediated acetylation reaction of pyrazolo­[1,5-a]­pyrimidines and a plausible mechanism based on density functional theory (DFT) theoretical calculations for this transformation are reported. Remarkably, and to the best of our knowledge, this is the first example of the direct acetylation for the functional pyrazolo­[1,5-a]­pyrimidine (PP) core. The synthesis of this essential building block is reported in high yields using mild reaction conditions, inexpensive reagents, and even substrates with electron-deficient or highly hindered groups. In addition, one of the new methyl ketones was successfully used as a substrate for producing novel and valuable bis-electrophilic compounds with yields of up to 90%. Notably, the discovered acetylation method was successfully applied in other π-excedent (N-hetero)­aromatic substrates.

Photophysical and anion sensing properties of a triphenylamine–dioxaborinine trimeric compound

“…Consequently, our previous results on constructing the dioxaborinine ring are a reliable starting point for accessing various derivatives of this heterocyclic core. 20 Additionally, it was possible to establish that the optimum temperature to treat the acetylating mixture (an excess of Ac 2 O/BF 3 ·OEt 2 ) is 60 °C. Finally, we could verify our hypothesis that the formation of the DB ring in a one-pot manner is enhanced when long reaction times are used.…”

“…During the optimizing reaction conditions process, we observed that the uorescent by-product 6, bearing the pyrazolo[1,5-a]pyrimidine-dioxaborinine hybrid system resulting from the formation of four new bonds in a one-pot manner, is favored in long reaction times. 20 Within the most conventional photophysical applications of organic uorophores, ion recognition has been the subject of extensive study in the last two decades; 21,22 in particular, cyanide (CN − ) is one of the most concerning environmental ions. Cyanide toxicity is known because it can inhibit the mitochondrial cytochrome C oxidase and suppress oxygen transport.…”

“…23,24 Consequently, the development of sensitive and selective probes for the sensing of this anion has been gaining considerable attention in recent years because of its essential role in a wide variety of biological, 25 environmental, 26 biochemical, 27 clinical, 28 synthetical due to design and preparation of the respective chemosensors and industrial applications. 21,22 Considering the above background and our continuing interest in obtaining new functional uorophores, 20,[29][30][31] we planned to develop the octupolar dye A2 by a synthesis implying the twelve new bonds formation in a one-pot manner (Scheme 2c). Fluorophore A2 is a tris-dioxaborinine-triphenylamine hybrid compound with promising photophysical properties in solution and solid-state, which we wish to study and compare with those for the similar dipolar system A1.…”

“…Considering the above background and our continuing interest in obtaining new functional fluorophores, 20,29–31 we planned to develop the octupolar dye A2 by a synthesis implying the twelve new bonds formation in a one-pot manner (Scheme 2c). Fluorophore A2 is a tris-dioxaborinine–triphenylamine hybrid compound with promising photophysical properties in solution and solid-state, which we wish to study and compare with those for the similar dipolar system A1 .…”

“…During the optimizing reaction conditions process, we observed that the fluorescent by-product 6, bearing the pyrazolo[1,5- a ]pyrimidine–dioxaborinine hybrid system resulting from the formation of four new bonds in a one-pot manner, is favored in long reaction times. 20 …”