Ligand-free nickel-catalyzed Kumada couplings of aryl bromides with tert-butyl Grignard reagents
A ligand-free nickel-catalyzed Kumada cross-coupling of aryl bromides and tert-butyl Grignard reagents led to the formation of a series of tert-butyl aryls in moderate to good yields, excellent tBu/iBu ratios, and good functional group compatibility. A radical coupling process is indicated and a mechanism with a Ni(I)-Ni(III) catalytic cycle is proposed.
The alkylation of anthracene by tert-butyl alcohol in the presence of trifluoro acetic acid or Lewis acids leads to the formation of 2-tert-butylanthracene and 2,6- and 2,7-di-tert-butylanthracenes.The ratio of 2,6- and 2,7-di-tert-butylanthracenes formed in the presence of trifluoroacetic acid and titanium tetrachloride is close to 75:25 and is determined by the relative alkylation rates of 2-tert-butylanthracene at positions 6 and 7.In the presence of aluminum chloride the ratio of the isomeric di-tert-butylanthracenes is 50:50 and is established as a result of the disproportionation and isomerization of the alkylation products.
Pozdnyakovich, Yu.V.
p. 527 - 531
(2007/10/02)
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