New Chemical Cross-Coupling between Aryl Halides and Allylic Acetates Using a Cobalt CatalystOrganic Letters,
5(7), 1043-1045 (2003)
DOI:
10.1021/ol0340641
Abstract The cobalt-catalyzed coupling reaction of aromatic halides and allylic acetates proceeds readily under mild conditions in the presence of the appropriate reducing agent
to produce allylaromatic derivatives either in pure acetonitrile (aryl bromides) or in acetonitrile/pyridine mixture (aryl chlorides).
In a typical procedure to MeCN (20 mL) was successively added Zn dust (3.25 g, 50 mmol), CoBr
2 (0.657 g, 3 mmol), ZnBr
2 (0.338 g, 1.5 mmol), and PhBr (0.16 g, 1.5 mmol). The reaction medium was activated by adding AcOH (0.024 g, 0.4 mmol) and stirred for 30 min at rt until PhBr was totally consumed. Allyl acetate (3.03 g, 30 mmol) and ethyl 4-bromobenzoate (2.427 g, 15 mmol) were then introduced into the soln. After being stirred for 3 h at rt, the reaction mixture was poured into a soln of 2M HCl (40 mL) and extracted with Et
2O (3x40 mL). The combined extracts were dried over MgSO
4. Evapn of Et
2O and purification by CC on SiO
2 afforded 1.852 g (65%) of ethyl 4-(2-propenyl)benzoate.
AcOH activates Zn dust. Addition of ZnBr
2 is not necessary but enhances the yield of the rxn. PhBr is added to decrease the amount of the reduction product (ArH). The second byproduct is Ar-Ar. The yields are within 31-75% (ArBr) and 15-83% (ArCl). Aryl zinc is postulated to be the rxn intermediate.
Supporting info: experimental details & characterization data.
(
http://pubs.acs.org/subscribe/journals/orlef7/suppinfo/ol0340641/ol0340641si20030225_035501.pdf)
For alternative methods see
Post 320892 (missing)
(Rhodium: "Allylbenzenes by Suzuki Coupling", Novel Discourse) ( >1 year old post, so I couldn't reply to it).