Palladium(II)-Catalyzed Oxidative C−H/C−H Cross-Coupling of Heteroarenes

Abstract

An efficient methodology for the synthesis of unsymmetrical biheteroaryl molecules has been developed via Pd(II)-catalyzed oxidative C-H/C-H cross-coupling of heteroarenes. An inversion in reactivity and selectivity has been achieved successfully to perform the desired heterocoupling. This process allows the heterocoupling of not only electron-rich N-containing heteroarenes (e.g., xanthines, azoles, and indolizines) but also electron-poor pyridine N-oxides with various thiophenes or furans.

Recent Progress in C—C Cross-Coupling Reaction of PyridineN-Oxides

“…前文介绍的吡啶-N-氧化物的 C-C 偶联反应一般 是和芳基卤化物(或磺酸芳香酯)、炔烃、烯烃(主要是缺 电子的或者电中性的)或者苯. You 等通过催化氧化的策 略来活化 C-H 键从而达到 C-C 偶联的目的, 并基于 此策略开发出吡啶-N-氧化物和富电子的杂环芳烃如呋 喃, 噻吩 [59] 和吲哚 [60] 的直接 C-C 键偶联的反应. 吡啶-N-氧化物(4 equiv.…”

Palladium‐Catalyzed Dehydrogenative Cross‐Couplings of Benzazoles with Azoles

“…[5] Hu, You, and co-workers reported on Pd(OAc) 2 -catalyzed copper-salt-activated CÀH/CÀH cross-couplings of xanthines, azoles, and electron-poor pyridine N-oxides with thiophenes and furans. [6] However, to date, efficient C À H/C À H crosscouplings between very similar partners, such as different azoles, remains a challenge because of their tendency to undergo homocoupling. [7] Hence, decarboxylative CÀH arylations were employed by Zhang and Greaney to link differently substituted azoles in moderate to good yield, but homocoupling was not fully suppressed and remained a limiting factor.…”

Palladium‐katalysierte dehydrierende Kreuzkupplungen von Benzazolen mit Azolen

“…[5] Hu, You und Mitarbeiter beschrieben Pd(OAc) 2 -katalysierte Kupfersalz-aktivierte C-H/ C-H-Kreuzkupplungen von Xanthinen, Azolen und elektronenarmen Pyridin-N-oxiden mit Thiophenen und Furanen. [6] Wegen ihrer Tendenz, Homokupplungen einzugehen, blieben jedoch bislang effiziente C-H/C-H-Kreuzkupplungen sehr ähnlicher Partner, z. B. verschiedener Azole, eine Herausforderung.…”

“…Ag + eingesetzt oder CuBr zugegeben wurde (Tabelle 1, Nr. 9-11), [6,14] ist das Kombinieren von Cu 2+ -und Ag + -Salzen ökonomischer und liefert bessere Ergebnisse (Tabelle 1, Nr. 5-7).…”