Ni-catalyzed coupling of BnCl + AcCl -> P2P
(Rated as: excellent)
Metallic Nickel-Mediated Synthesis of Ketones by the Reaction of Benzylic Halides with Acid Halides
J. Org. Chem. 50, 1373-1381 (1985)
Preparation of Metallic Nickel
A 50-mL two-neck flask was equipped with a magnetic stirrer, a rubber septum, and a condenser topped with argon inlet and outlet to oil pump. Lithium metal was cut under mineral oil. One piece of lithium with a shining metal surface was rinsed in hexane and transferred into a glass tube with a stopcock and a rubber septum which had been filled with argon. The glass tube was evacuated to evaporate the hexane, filled with argon, and weighed. Nickel halide (1.0 equiv, 9-13 mmol), lithium (2.3 equiv, 21-30 mmol), and naphthalene (0.1 equiv, 0.9-1.3 mmol) were placed in the flask through the side neck. The flask was evacuated and filled with argon two or three times. The use of a glovebox or -bag is not required if contact of the lithium with air is kept to a minimum. Then, glyme (25-30 mL) was added through the septum with a syringe, and the mixture was stirred for 12 h. During the reduction the surface of lithium became pink. After the lithium metal was consumed completely, the stirring was stopped; metallic nickel which had adhered to the walls of the flask was scraped off with the stirrer and a magnet. The nickel precipitated as a bulky black powder in a clear colorless solution after standing. The septum on the side neck was replaced with an addition funnel, and a mixture of appropriate reagents in glyme (10 mL) was then added to the nickel.
Reaction of Benzyl Chloride with Acetyl Chloride in the Presence of Metallic Nickel
Metallic nickel in glyme (25 mL), prepared from nickel iodide (2.97 mmol), lithium (0.152 g, 21.9 mmol), and naphthalene (0.122 g, 0.95 mmol), was heated to reflux. A mixture of benzyl chloride (1.0 g, 7.9 mmol) and acetyl chloride (0.65 g, 8.3 mmol) in glyme (10 mL) was added dropwise for 30 min. Additional heating was continued for 15 min, and the red-brown reaction mixture was cooled to room temperature, poured into a separatory funnel containing hydrochloric acid solution (37%, 100 mL), and extracted with chloroform twice. The chloroform solution was washed with water, and the aqueous phase was extracted with additional chloroform. The combined extracts were dried over anhydrous sodium sulfate and concentrated. The crude oil was purified by silica gel chromatography. It was eluted with hexane followed by chloroform to give phenyl-2-propanone (0.72 g, 68%), bp 95-96°C (11 mmHg); IR (neat) 1710 cm-1 (C=O).
Metallic Nickel: A Coupling Reagent Of Benzyl Halides And Acyl Halides To Yield Benzyl Ketones
Tetrahedron Letters 24(24), 2451-2452 (1983) (The preliminary communication by the same authors)
Metallic nickel was prepared in glyme (25 ml) by the reduction of nickel iodide (2.97 g, 9.50 mmol) with lithium (0.152 g, 21.9 mmol) using naphthalene (0.122 g, 0.95 mmol) as an electron carrier. After stirring these reagents under an atmosphere of argon at room temperature for 12 hr, the finely divided nickel appeared as a black powder which settled in a clear colorless solution. To the nickel powder in refluxing glyme, a mixture of benzyl chloride (0.915 g, 7.24 mmol) and acetyl chloride (0.6 g, 7.61 mmol) in glyme (10 ml) was added dropwise for 30 min. Additional heating was continued for 15 min and the red-brown reaction mixture was poured into separatory funnel containing 3% hydrochloric acid solution (100 ml) and was extracted with chloroform. The aqueous phase was extracted with chloroform and the combined extracts were washed with water, dried over anhydrous sodium sulfate, and concentrated. Crude oil was submitted on silica gel chromatography eluted with chloroform to give phenyl-2-propanone (68% yield); bp 95-96°C/11mmHg. Bibenzyl formed by the homo-coupling reaction of benzyl chloride was also isolated in 14% yield.
The reductive coupling reaction of benzyl chloride with benzoyl chloride proceeded even at room temperature, however, improved results were obtained under refluxing glyme (at 85°C). The choice of nickel halide reduced was important and metallic nickel prepared from other nickel halides gave much lower yields. Thus, the reaction of benzyl halides with acyl halides using metallic nickel derived from nickel iodide was carried out under refluxing glyme. The reaction may be reasonably explained by the smooth oxidative addition of halides to nickel to afford benzylnickel and acylnickel halides. The metathesis of these complexes could give the acylbenzylnickel complex, which upon reductive elimination would yield the benzyl ketone.