Recent developments and trends in the iron- and cobalt-catalyzed Sonogashira reactions

Abstract

Iron- and cobalt-catalyzed Sonogashira coupling reactions are becoming central areas of research in organic synthesis. Owing to their significant importance in the formation of carbon–carbon bonds, numerous green and nanoparticle protocols have emerged during the past decades. The non-toxic and inexpensive nature of catalysts gained much attention in recent times. In this context, their catalytic nature and activity in Sonogashira coupling reactions were well explored and compared. Most importantly, one of the highlights of this review is the emphasis given to green strategies. This is the first review on iron- and cobalt-catalyzed Sonogashira coupling reactions which comprehends literature up to 2020.

Nickel‐Catalyzed Sonogashira Couplings: Extending the Reaction Scope to Aryl Bromides and Chlorides

“…Considerable efforts towards nickel [14] and copper [15] catalysis have been made over the last years. The use of iron and cobalt complexes has also been explored to a lesser extent [16] …”

“…The use of iron and cobalt complexes has also been explored to a lesser extent. [16] Nickel has emerged as a promising alternative to palladium catalysis. [17] Both transition metals belong to the same group in the periodic table and share the d 10 electronic configuration.…”

Cross‐Coupling Between Aryl Halides and Aryl Alkynes Catalyzed by an Odd Alternant Hydrocarbon

“…[4][5][6][7] Initial modifications focused on the exclusion of copper [8,9] from the reaction condition, and later the reaction further flourished even with the replacement of palladium catalysts with other lighter transition metal-based catalysts [10,11] (Figure 1a), as the high cost of the palladium, its toxicity, and removal of ppm-level impurities from the products have been long-standing challenges. [12,13] As a result, various reports are known for Sonogashira coupling reactions under palladium metal-free conditions, using copper , [14,15] iron , [16,17] cobalt , [17] ruthenium [18] and Ni [19,20] catalysts resulting in the cross-coupling between aryl halides and terminal alkyne partners (Figure 1a). Furthermore, several heterogeneous transition metal-based catalytic procedures [21,22] have also been explored for this cross-coupling reaction which generally operates at higher temperatures or under microwave [23,24] /photostimulation.…”

A Solely Fe‐Catalyzed Sonogashira‐Type Coupling of non‐Activated Secondary Alkyl Iodides with Terminal Alkynes

“…Representative examples of iron-catalyzed Sonogashira reactions are summarized on the Scheme 1. They are mostly limited to aryl iodides [15][16][17][18][19][20] and usually require the presence of a ligand such as a phosphine or a bidentate N,N-ligand, copper as cocatalyst, high temperatures (over 100 °C) and prolonged reaction time. So far, non-activated secondary alkyl halides remain challenging substrates for Fecatalyzed Sonogashira chemistry, due to the proficiency of β-elimination side reactions occurring in those substrates.…”