Palladium-Catalyzed Acetylation of Arylbromides

Abstract

6-Acetylbenzothiophene (1). A single-necked (24/40 joint) 250 mL roundbottomed flask is equipped with a Teflon-coated magnetic stir bar (4.0 x 1.5 cm, football-shaped). The apparatus is flame-dried under vacuum, then cooled to 23 oC under an atmosphere of argon (Note 2). The flask is charged sequentially with 6-bromobenzothiophene (8.00 g, 37.5 mmol, 1 equiv) (Note 3), cesium fluoride (22.8 g, 150 mmol, 4 equiv) (Note 4), and tetrakis(triphenylphosphine)palladium(0) (2.17 g, 1.88 mmol, 0.05 equiv) (Note 4) through the neck of the flask in singular portions. The neck of the flask is then fit with a rubber septum. An argon inlet needle and a purge needle are placed in the rubber septum, and the flask is purged for 5 min (Figure 1A). After 5 min, the vent needle is removed, and acetyltrimethylsilane (10.8 mL, 75 mmol, 2 equiv) (Note 5) is added in one portion over 1 min via a plastic syringe fit with an 18 G x 1.5’’ needle. 1,2-Dichloroethane (38 mL, 1 M) (Note 6) is then added to the flask via a plastic syringe fit with an 18 G x 6’’ needle in a single portion over 1 min (Figure 1B). The rubber septum is quickly removed and replaced with a Pd(PPh3)4 (5.0 mol%) CsF