Jackson EP, Montgomery J. Regiocontrol in catalytic reductive couplings through alterations of silane rate dependence.
J Am Chem Soc 2015;
137:958-63. [PMID:
25531576 PMCID:
PMC4356119 DOI:
10.1021/ja511778a]
[Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
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Combinations of ligand, reducing
agent, and reaction conditions
have been identified that allow alteration in the rate- and regioselectivity-determining
step of nickel-catalyzed aldehyde–alkyne reductive couplings.
Whereas previously developed protocols involve metallacycle-forming
oxidative cyclization as the rate-determining step, this study illustrates
that the combination of large ligands, large silanes, and elevated
reaction temperature alters the rate- and regiochemistry-determining
step for one of the two possible product regioisomers. These modifications
render metallacycle formation reversible for the minor isomer pathway,
and σ-bond metathesis of the metallacycle Ni–O bond with
the silane reductant becomes rate limiting. The ability to tune regiocontrol
via this alteration in reversibility of a key step allows highly regioselective
outcomes that were not possible using previously developed methods.
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