Abstract
An operationally simple cross-coupling reaction between aryl
halides and alkyl halides with high selectivity has been developed.
The underlying domino process utilizes CoCl2 /Me4 -DACH
as a catalyst system. The methodology exhibits high sustainability
as it obviates the need for the pre-formation and handling of stoichiometric
amounts of hazardous Grignard compounds.
Keywords
cobalt - cross-coupling - aryl halides - domino
reactions
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14b General procedure:
A 10 mL flask was placed in a water bath (r.t.), charged with Mg
turnings (63 mg, 2.6 mmol), fitted with a rubber septum, and purged
with argon (1 min). A solution of CoCl2 (13 mg, 0.1 mmol,
5 mol%) and Me4 -DACH (35 µL, 0.2 mmol,
10 mol%) in anhydrous THF (4 mL) was added via syringe.
The mixture was stirred at r.t. for 15 min, then the reaction was
cooled to 0 ˚C and aryl bromide (2.4 mmol) and
alkyl bromide (2.0 mmol) were added. After 6 h at 0 ˚C,
the reaction was quenched with saturated aqueous NH4 Cl
(5 mL) and aqueous HCl (10%, 2 mL) and extracted
with ethyl acetate (3 × 5 mL). The combined
organic phases were dried over Na2 SO4 , concentrated
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Scheme 2. A small portion of biaryl might also result from a cobalt-catalyzed
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20 Reactions with (-)-sparteine
and quinine as chiral ligands instead of Me4 -DACH each
afforded 3q in <7% yield
(ee was not determined)