Infrared Irradiation-Assisted Pd-Catalyzed C(sp³)─H Arylation and Tandem Cyclization of Ortho-Tolualdehydes

Herein, we describe the use of IR irradiation to promote Pd-catalyzed C(sp³)─H arylation and tandem C(sp³)─H arylation/electrophilic aromatic cyclization of ortho-tolualdehydes with aryl iodides via a transient directing group (TDG) strategy. The optimized conditions employ Pd(OAc)₂ (10 mol%) as the catalyst, glycine (40 mol%) as the TDG, and AgTFA (1.5 equiv.) as the additive in an AcOH/H₂O (9:1, v/v) solvent mixture under irradiation with a 250 W IR lamp. The reaction time (30 min) is considerably shorter than previously reported reaction times for similar reactions performed under thermal heating (12-48 h, 90°C-130°C). The reaction outcome under infrared (IR) irradiation strongly depends on the electronic nature of the substituents on the aryl iodides: electron-withdrawing groups at any position and electron-donating groups at the ortho and/or para positions favor the Pd-catalyzed C(sp³)─H arylation, leading to 2-benzylbenzaldehydes, whereas, in the presence of electron-donating groups at the meta-position, a tandem C(sp³)─H arylation/electrophilic aromatic cyclization occurs, producing substituted anthracenes.