Ligand-Dependent Scope and Divergent Mechanistic Behavior in Nickel-Catalyzed Reductive Couplings of Aldehydes and Alkynes
Gireesh M. Mahandru, Gang Liu and John Montgomery*
*University of Michigan, Department of Chemistry, 930 N. University, Ann
Arbor, MI 48109-1055, Email: jmontg
umich.edu
G. M. Mahandru, G. Liu, J. Montgomery, J. Am. Chem. Soc., 2004, 126, 3698-3699.
DOI: 10.1021/ja049644n
Abstract
A new procedure for catalytic reductive coupling of aldehydes and alkynes uses Ni(COD)2 with an imidazolium carbene ligand as the catalyst and triethylsilane as the reducing agent.
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Details
This study by Mahandru, Liu, and Montgomery explores the ligand-dependent scope and mechanistic behavior in nickel-catalyzed reductive couplings of aldehydes and alkynes. The researchers developed a new procedure using a nickel carbene catalyst, which showed significantly different reactivity compared to the previously used Ni(COD)2/PBu3 catalyst. The new method involves the three-component addition of aldehydes, alkynes, and triethylsilane, yielding good to excellent results across a broad range of substrates. The study highlights the broad scope, stability, and selectivity of the new procedure, which also incorporates a convenient hydroxyl protecting group.
Mechanistic studies revealed that the Ni(0) catalysts with PBu3 and heterocyclic carbenes operate via different mechanisms. Crossover experiments using deuterium-labeled silanes demonstrated that the two catalyst systems proceed through fundamentally different pathways. The findings necessitated a revision of the previously proposed mechanism for the PBu3-based procedure. The study concludes that the new nickel carbene catalyst system offers an efficient and selective method for reductive couplings, with significant mechanistic insights that could aid in the development of other metal-catalyzed processes. The research was supported by NIH and a Johnson and Johnson Focused Giving Award.
A General Strategy for Regiocontrol in Nickel-Catalyzed Reductive Couplings of Aldehydes and Alkynes
H. A. Malik, G. J. Sormunen, J. Montgomery, J. Am. Chem. Soc., 2010, 132, 6304-6305.
K. Sa-ei, J. Montgomery, Org. Lett., 2006, 8, 4441-4443.
Key Words
Allylic Alcohols, Silyl Ethers, Triethylsilane, Multicomponent Reactions
ID: J48-Y2004-1430
