Iridium‐Catalyzed Hydroarylation via C−H Bond Activation

Abstract

Hydroarylation reactions via CÀ H activation, which compensate for shortcomings of classical methods based on the Friedel-Crafts reaction, is one of the most attractive methods to synthesize substituted arenes. This Personal Account reviews our recent studies on iridiumcatalyzed intermolecular hydroarylation of vinyl ethers, alkynes, bicycloalkenes, and 1,3-dienes, and intramolecular hydroarylation of m-allyloxyphenyl ketones, where asymmetric addition reactions are included. A cationic iridium catalyst, which is generated from chloroiridium [IrCl] and NaBAr F 4 [Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ], or a hydroxoiridium [Ir(OH)] complex is effective in catalyzing the hydroarylation depending on the substrates. 1,5-Cyclooctadiene (cod), chiral dienes, and conventional bisphosphines function as ligands controlling the high reactivity and selectivity of the catalysts in the hydroarylation. H/D exchange reaction of alkenes by use of a key intermediate of the hydroarylation reaction is also described.

Chiral Diene Ligands in Asymmetric Catalysis

“…The functionalization of aromatic C–H bonds has realized the step-economic synthesis of useful compounds in organic chemistry; hence, the development of asymmetric reactions involving C–H functionalization is important and challenging subject. This section describes asymmetric C–C bond-forming reactions catalyzed by chiral diene–metal complexes where organometallic intermediates are generated by the metalation of an aromatic or vinylic C–H bond …”

“…This section describes asymmetric C−C bond-forming reactions catalyzed by chiral diene−metal complexes where organometallic intermediates are generated by the metalation of an aromatic or vinylic C−H bond. 265 Iridium-catalyzed [3 + 2] annulation with 1,3-dienes, which was first reported in the reaction of cyclic N-sulfonyl ketimines 305 (Scheme 61a), 266 has been successfully extended to the asymmetric version in the reaction of cyclic N-acyl ketimines 229 generated in situ by the dehydration of 3-aryl-3hydroxyisoindolin-1-ones 228 (Scheme 61b). 267 Thus, the reaction of 228 with 1,3-dienes 306, typically isoprene, took place with high regio-and enantioselectivity in the presence of DABCO and a cationic chiral diene−iridium complex generated from [IrCl((S,S)-L14a)] 2 and NaBAr F 4 , giving the corresponding spiroaminoindane derivatives 307 in high yields.…”

Recent advances in the functionalization of azulene through Rh‐, Ir‐, Ru‐, Au‐, Fe‐, Ni‐, and Cu‐catalyzed reactions

“…[18] Iridium catalysts have been tested in this regard for a variety of reactions including isomerization, [19] hydrogenation, [20,21] hydrazine decomposition, hydroarylation reactions via CH activation, and hydrogenolysis reactions. [22][23][24] Because of its ability to produce highly versatile aryl organoboronate ester intermediates from arenes without the use of reactive groups such as halides or sulfonates, iridium-catalyzed CH borylation of arenes has also proven to be a method for the functionalization of arenes. [21]…”

Enantioselective C−H Functionalization Reactions under Gold Catalysis

“…As a solution to tackle this problem, transition metal complexes have often been exploited as catalysts. Among all transition metals, the complexes of 4d and 5d elements such as Pd, [6] Rh, [7] Ru, [8] Ir, [9] etc. have dominated the field.…”