Communications
[NiCl2(PCy3)2] (69.0 mg, 0.0999 mmol), PCy3 (57.8 mg, 0.206 mmol),
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for 15 h. The microwave reaction was heated for 30 min.
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[13] Several organomagnesium derivatives were screened to delin-
eate their scope in the cross-coupling. It was found that only aryl
Grignard reagents participate in the reaction; alkyl and alkenyl
Grignard reagents return only the starting anisole derivative
under a variety of conditions.
tridecane (328 mg, 1.778 mmol, as an internal standard), and N,N-
dimethyl-N-[2-(5,6,7,8-tetrahydronaphthalen-2-yloxy)ethyl]amine
(409 mg, 1.867 mmol). The solvent in the p-TolMgBr reagent (1m in
ether, 6.0 mmol) was removed under reduced pressure and replaced
with diethoxymethane (6.0 mL). This solution was then added to the
above catalyst mixture under a nitrogen atmosphere at room
temperature. The resulting solution was stirred for several minutes
at room temperature and then warmed to 958C for 15 h. A sample
was withdrawn and quenched by adding it to 1m aqueous sodium
citrate, which was then extracted with ethyl acetate. GC analysis of
the organic phase showed the presence of 6-(4-methylphenyl)-1,2,3,4-
tetrahydronaphthalene (1.85 mmol, 99% conversion), bitoluene
(0.65 mmol), and p-methylphenol (0.58 mmol) in the reaction mix-
ture. In general, the optimal conditions for each substrate had to be
determined by experimentation. The temperature for the cross-
coupling was found to range from room temperature to 1008C
depending on the steric nature of the anisole. In general, the most
effective catalyst system was either [NiCl2(PCy3)2], [NiCl2(PCy3)2]/
2PCy3, or [NiCl2(PhPCy2)2]. The most useful solvents were found to
be tAmOMe, (EtO)2CH2, PhMe, and tBuOMe. The choice of solvent
was found to depend on the temperature of the reaction and the
solubility of the Grignard reagent in the selected solvent. In general,
the Grignard reagents were found to be most soluble in PhMe;
however, this was not usually the best solvent for the cross-coupling
procedure. In some cases it was best to use a mixture of PhMe and one
of the ether solvents listed above. The most general and effective
conditions were the use of 5 mol% [NiCl2(PhPCy2)2] in tAmOMe at a
temperature determined primarly by the steric hindrance of the
anisole. The reactions were over after 15 h reaction time (at 808C);
however, in some cases the reaction can reach completion in as little
as 3 h. Activated anisole compounds (2-methoxypyridine, 1- and 2-
methoxynaphthalene) could be coupled using a variety of nickel
complexes such as [NiCl2(PMe3)2] or [Ni(acac)2]/neopentylphosphite
in THF.
Received: January 15, 2004 [Z53765]
À
Keywords: anisole · biaryls · C C coupling · nickel ·
phosphane ligands
.
[1] For general references, see: E.-i. Negishi, F. Liu in Metal-
Catalyzed Cross-Coupling Reactions, Vol. 1 (Eds.: F. Diederich,
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Angew. Chem. Int. Ed. 2004, 43, 2428 –2432