Infrared Irradiation‐Assisted Pd‐Catalyzed C(sp 3 )─H Arylation and Tandem Cyclization of Ortho ‐Tolualdehydes
Matteo Renato Martina, Ambra Maria Fiore, Angela Punzi, Gianluigi Albano, Roberta Ragni, Pietro Cotugno, Gianluca Maria FarinolaABSTRACT
Herein, we describe the use of IR irradiation to promote Pd‐catalyzed C(sp 3 )─H arylation and tandem C(sp 3 )─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/H 2 O (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(sp 3 )─H arylation, leading to 2‐benzylbenzaldehydes, whereas, in the presence of electron‐donating groups at the meta ‐position, a tandem C(sp 3 )─H arylation/electrophilic aromatic cyclization occurs, producing substituted anthracenes.