Abstract
A highly efficient acylative cross-coupling of trialkylboranes with activated amides has been effected at room temperature to give the corresponding alkyl ketones in good to excellent yields by using 1,3-bis(2,6-diisopropyl)phenylimidazolylidene and 3-chloropyridine co-supported palladium chloride, the PEPPSI catalyst, in the presence of K2CO3 in methyl tert-butyl ether. The scope and limitations of the protocol were investigated, showing good tolerance of acyl, cyano, and ester functional groups in the amide counterpart while halo group competed via the classical Suzuki coupling. The trialkylboranes generated in situ by hydroboration of olefins with BH3 or 9-BBN performed similarly to those separately prepared, making this protocol more practical.
Highlights
Amides are unique and ubiquitous substructures in natural and artificial organic functional molecules, because the strong resonance between the carbonyl and amino groups leads to a highly inert and significantly planar linkage
In the past three years, many efforts have been made to expand the scope of amide counterparts, developing a variety of activated amides suitable for the acylative cross-coupling, e.g., N-acyl imides [4,5,6], N-Boc and N-Ts/Ms amides [7,8,9,10,11,12,13,14,15], N-acylsaccharins [16,17,18,19,20], and amides of heteroaromatic compounds [21,22]
Bases appeared to play a key role in the reaction, among which K2 CO3 performed best in Methyl tert-butyl ether (MTBE) at room temperature
Summary
Amides are unique and ubiquitous substructures in natural and artificial organic functional molecules, because the strong resonance between the carbonyl and amino groups leads to a highly inert and significantly planar linkage. The carbon-centered nucleophile counterparts are still rather undeveloped, in particular, with respect to alkyl ones, alkyl ketones have been widely found in biologically important molecules and synthetic building blocks for fine chemicals. Besides the closely related esters [23,24,25], there are only two reports on the acylative cross-coupling of amides with alkyl reagents effected by using nickel catalysts. Garg and co-workers reported the first alkylation of amide derivatives by nickel-catalyzed acylative coupling with alkyl zinc reagents in
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