A new
method for the decarboxylative coupling of alkyl N-hydroxyphthalimide esters (NHP esters) with aryl
iodides is presented. In contrast to previous studies that form alkyl
radicals from carboxylic acid derivatives, no photocatalyst, light,
or arylmetal reagent is needed, only nickel and a reducing agent (Zn).
Methyl, primary, and secondary alkyl groups can all be coupled in
good yield (77% ave yield). One coupling with an acid chloride is
also presented. Stoichiometric reactions of (dtbbpy)Ni(2-tolyl)I with
an NHP ester show for the first time that arylnickel(II) complexes
can directly react with NHP esters to form alkylated arenes.
Cross-electrophile coupling of aryl halides with alkyl halides has thus far been primarily conducted with stoichiometric metallic reductants in amide solvents. This report demonstrates that the use of tetrakis(dimethylamino)ethylene (TDAE) as an organic reductant enables the use of non-amide solvents, such as acetonitrile or propylene oxide, for the coupling of benzyl chlorides and alkyl iodides with aryl halides. Furthermore, these conditions work for several electron-poor heterocycles that are easily reduced by manganese. Finally, we demonstrate that TDAE addition can be used as a control element to 'hold' a reaction without diminishing yield or catalyst activity.
Conjugate addition
of organometallic reagents to enones to form
silyl enol ether products is a versatile method to difunctionalize
activated olefins, but the organometallic reagents required can be
limiting. The reductive cross-electrophile coupling of unhindered
primary alkyl bromides with enones and chlorosilanes to form silyl
enol ether products is catalyzed by a nickel-complexed ortho-brominated terpyridine ligand. The conditions are compatible with
a variety of cyclic/acyclic enones and functional groups.
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