Infrared Irradiation‐Assisted Solvent‐Free Pd‐Catalyzed (Hetero)aryl‐aryl Coupling via C−H Bond Activation

Abstract

The increasing attention towards environmentally friendly synthetic protocols has boosted studies directed to the development of green and sustainable methods for direct C−H bond arylation of (hetero)arenes. In this context, here the infrared (IR) irradiation‐assisted solvent‐free Pd‐catalyzed direct C−H bond arylation of (hetero)arenes was achieved. Several heteroaryl‐aryl coupling reactions were described, also involving heterocycles commonly used as building blocks for the synthesis of organic semiconductors. The reaction tolerated many functional groups on the aromatic nuclei. The IR‐irradiation as the energy source compared favorably with thermal heating and, in combination with solvent‐free conditions, provided an important contribution to the development of protocols fitting with the principles of green chemistry.

Palladium-catalyzed cross-dehydrogenative coupling of (hetero)arenes

“…Scheme 44 IR irradiation-assisted Pd-catalyzed CDC reactions of polyfluoroarenes with heteroarenes, reported in 2023 by Farinola and coworkers. 100 isotope effect (k H /k D = 2.19) was found for the reaction of C 6 F 6 H with 2-n-octylthiophene/2-n-octylthiophene-d 1 under thermal heating, indicating that the C-H bond activation of the heteroarene was the rate-determining step. Very surprisingly, by repeating the same experiments under IR irradiation, no significant KIE was found with respect to both coupling partners: the RDS was no longer the Pd-promoted C-H bond activation of the heteroarene (Scheme 44c).…”

“…100 IR irradiation has recently earned considerable attention as a non-conventional energy source in organic synthesis, minimizing reaction times and improving product yields with respect to traditional thermal heating. 101 However, its beneficial role has never been investigated in detail, since it was simply explained as a very efficient form of heating. With the aim of elucidating the actual role of IR irradiation in promoting organic reactions which typically require a high thermal activation energy, here the authors developed the first IR irradiation-assisted methodology for Pd-catalyzed CDC reactions, selecting polyfluoroarenes and heteroarenes with relatively acidic C–H bonds as the two coupling partners.…”

“…Very recently, an appealing protocol for Pd-catalyzed CDC reactions of polyfluoroarenes with heteroarenes was reported by Farinola and co-workers, involving the use of infrared (IR) irradiation instead of the traditional thermal heating (Scheme 44). 100 IR irradiation has recently earned considerable attention as a non-conventional energy source in organic synthesis, minimizing reaction times and improving product yields with respect to traditional thermal heating. 101 However, its beneficial role has never been investigated in detail, since it was simply explained as a very efficient form of heating.…”

Photoinduced Bisphosphination of Alkynes with Phosphorus Interelement Compounds and Its Application to Double-Bond Isomerization

“…This addition reaction is promoted by transition-metal catalysts, acids, bases, and radical initiators [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. On the other hand, photoirradiation has recently attracted much attention as a clean, ecofriendly, and powerful method in organic synthesis [27][28][29]. Thus, given the drawbacks of conventional methods, photoirradiation-induced radical addition reactions, which do not require additives, are becoming increasingly important from the viewpoint of green innovation [30,31].…”

A Four-Component Reaction for the Synthesis of Thienopyrrolediones under Transition Metal Free Conditions

“…Then TPD-H 2 is generated via a Sandmeyer reaction and neat condensation with alkylamine . Various useful π–A−π type building blocks can be achieved via Pd- or Cu-catalyzed C–H arylations with aromatic halides (Scheme , b) . Each of these various methods has its own merits, but they also suffer from deficiencies such as multiple steps, toxic organotin reagents, and transition-metal catalysts.…”