Palladium-Catalyzed Alkyl-Alkyl Suzuki Cross-Couplings of Primary Alkyl Bromides at Room Temperature

Abstract

A. 1-Bromo-8-chlorooctane (1). An oven-dried, 200-mL, two-necked, round-bottomed flask equipped with an argon inlet and a magnetic stirbar (octagonal, molded pivot ring, 25 mm length and 6 mm diameter) is purged with argon for 5 min and then charged through the open neck with CH2Cl2 (50 mL via syringe) (Note 1), imidazole (2.19 g, 32.1 mmol, 1.10 equiv) (Note 2), and dichlorotriphenylphosphorane (10.4 g, 31.2 mmol, 1.07 equiv) (Note 3). The open neck is capped with a rubber septum, and the stirred solution is cooled in an ice bath for 5 min. A solution of 8-bromo-1-octanol (5.0 mL, 6.11 g, 29.2 mmol, 1.00 equiv) (Note 4) in CH2Cl2 (10 mL) (Note 1) is added via syringe over 5 min. The reaction mixture is allowed to warm to rt, and the resulting heterogeneous solution (a white precipitate formed) is stirred for 4 h. The progress of the reaction is followed by TLC analysis on SiO2 (10% EtOAc/hexanes as the eluent; visualization with a KMnO4 stain; the alcohol starting material has an Rf = 0.2, and the chloride product has an Rf = 0.9) (Note 5). After the alcohol is consumed, the reaction is diluted with pentane (200 mL), and the mixture is filtered through a pad of SiO2 (7 cm diameter ���� 6 cm height) in a sintered glass funnel. The SiO2 is washed with additional pentane (400 mL). The filtrate is concentrated by rotary evaporation (20 mmHg, 30 °C), which furnishes the desired product as a colorless oil (6.23–6.44 g, 94–97 % yield) (Note 6). The product is used in the next step without further purification.