Non-Palladium-Catalyzed Oxidative Coupling Reactions Using Hypervalent Iodine Reagents

Abstract

Transition metal-catalyzed direct oxidative coupling reactions via C–H bond activation have emerged as a straightforward strategy for the construction of complex molecules in organic synthesis. The direct transformation of C–H bonds into carbon–carbon and carbon–heteroatom bonds renders the requirement of prefunctionalization of starting materials and, therefore, represents a more efficient alternative to the traditional cross-coupling reactions. The key to the unprecedented progress made in this area has been the identification of an appropriate oxidant that facilitates oxidation and provides heteroatom ligands at the metal center. In this context, hypervalent iodine compounds have evolved as mainstream reagents particularly because of their excellent oxidizing nature, high electrophilicity, and versatile reactivity. They are environmentally benign reagents, stable, non-toxic, and relatively cheaper than inorganic oxidants. For many years, palladium catalysis has dominated these oxidative coupling reactions, but eventually, other transition metal catalysts such as gold, copper, platinum, iron, etc. were found to be promising alternate catalysts for facilitating such reactions. This review article critically summarizes the recent developments in non-palladium-catalyzed oxidative coupling reactions mediated by hypervalent iodine (III) reagents with significant emphasis on understanding the mechanistic aspects in detail.

Iodine(V)-Based Oxidants in Oxidation Reactions

“…These reagents are potential oxidants due to their excellent oxidizing and electrophilic properties [ 9 , 10 , 11 , 12 , 13 ]. The unique characteristics attributed to these reagents are non-toxicity, easy handling, high reactivity and stability, combined with good site selectivity and broad applicability in several synthetic transformations [ 14 , 15 , 16 ]. Therefore, hypervalent iodine reagents are of paramount importance to organic chemistry for the development of new asymmetric and non-asymmetric reactions.…”

Catalytic stereoselective synthesis involving hypervalent iodine-based chiral auxiliaries

“…16–19 In addition, a serious problem associated with transition-metal-promoted reaction is the product contamination, which is not observed with iodine( iii / v ) reagents. Therefore, hypervalent iodine compounds are potential rivals to transition metals in many organic reactions as covered in several excellent review articles, 20–30 book chapters, and books. 31–39…”

“…[16][17][18][19] In addition, a serious problem associated with transition-metal-promoted reaction is the product contamination, which is not observed with iodine(III/V) reagents. Therefore, hypervalent iodine compounds are potential rivals to transition metals in many organic reactions as covered in several excellent review articles, [20][21][22][23][24][25][26][27][28][29][30] book chapters, and books. [31][32][33][34][35][36][37][38][39] Traditionaly, hypervalent iodine reagents are employed as stoichiometric reagents but recent studies have revealed their use as versatile catalysts, as reviewed by Singh, Wirth, and coworkers.…”

Balancing connectivity with function in silver(i) networks of pyridyltriazole (tzpa) ligands results in the formation of a metallogel

“…The C-H arylation of arenes, heteroarenes, alkenes, and alkanes by diaryliodonium salts has been achieved using a variety of different metal salts as catalysts; representative examples with some or all of these substrates are known with Pd [5], Pt, Au, Cu, Fe, Ir, Ni, and Ru salts [6]. Diaryliodonium salts are also known to arylate a wide variety of nucleophiles such as enolates, carboxylates, amides, alkoxides, halides, etc.…”