Stepwise synthesis of 2,6-difunctionalized ethyl pyrazolo[1,5-a]pyrimidine-3-carboxylate via site-selective cross-coupling reactions: experimental and computational studies

A variety of novel disubstituted 2-(alknyl, aryl and arylamine)-6-alkynylpyrazolo[1,5-a]pyrimidine derivatives was prepared via sequential site-selective cross-coupling reactions from 2,6-dibromopyrazolo[1,5-a]pyrimidine 3. The regio-controlled Sonogashira-type coupling of 3 with a wide range of terminal alkynes proceeded smoothly with excellent selectivity in favor of the C6-position through careful adjustment of the coupling conditions, followed by the subsequent introduction of alkynyl, aryl or arylamine groups at the C2-position via the Sonogashira, Suzuki-Miyaura and Buchwald-Hartwig coupling reactions, respectively. These promising results allow for further use and diversification of the chemically and biologically interesting pyrazolo[1,5-a]pyrimidine scaffold. In addition, computational studies were conducted to provide explanations for the origin of regioselectivity.

Recent advances in transition metal-catalysed cross-coupling of (hetero)aryl halides and analogues under ligand-free conditions

The formation of new bonds is pivotal in organic chemistry and a prerequisite to life because it allows the construction of complex molecules from simple precursors.

Application of the Suzuki-Miyaura reaction in the synthesis of flavonoids

The application of the Suzuki-Miyaura reaction in the synthesis of flavonoids, an important class of natural products, is reviewed. This reaction has not only been employed to provide access to flavonoid nuclei, but has also been applied to the synthesis of dimeric flavonoids and in the synthesis of libraries of flavonoid derivatives for biological activity studies. The classes of flavonoids that are discussed are the chalcones, flavones, isoflavones, neoflavones, biflavones and derivatives of flavonoids obtained by C-C bond formation via the Suzuki-Miyaura reaction.