title: A Robust Protocol for Pd(II)-catalyzed C-3 Arylation of (1H) Indazoles and Pyrazoles: Total Synthesis of Nigellidine Hydrobromide.
abstract: C3-arylated indazole and pyrazoles are privileged structural motifs in agrochemicals and pharmaceuticals. C-3 C-H arylation of (1H) indazole and pyrazole has been a significant challenge due to the poor reactivity of the C-3 position. Herein, we report a practical Pd(II)/Phen catalyst and conditions for direct C-3 arylation of indazole and pyrazole with ArI or ArBr without using Ag additives as halide scavengers. The use of toluene, chlorobenzene, trifluoromethylbenzene and mesitylene as the solvent was found to be crucial for the selectivity and reactivity. We further demonstrate the robustness of this protocol through the first total synthesis of Nigellidine hydrobromide as well as expedient preparation of heterocycles structurally related to pesticides and drug molecules.
authors.affiliation: Department of Chemistry, The Scripps Research Institute, 10550 N. Torrey Pines Rd., La Jolla, CA, 92037, USA.
authors.forename: Mengchun
authors.initials: M
authors.lastname: Ye
authors.forename: Andrew J F
authors.initials: AJ
authors.lastname: Edmunds
authors.forename: James A
authors.initials: JA
authors.lastname: Morris
authors.forename: David
authors.initials: D
authors.lastname: Sale
authors.forename: Yejia
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jin-Quan
authors.initials: JQ
authors.lastname: Yu