N-Acyl-5,5-Dimethylhydantoins: Mild Acyl-Transfer Reagents for the Synthesis of Ketones Using Pd–PEPPSI or Pd/Phosphine Catalysts

Classes of Amides that Undergo Selective N-C Amide Bond Activation: The Emergence of Ground-State Destabilization

Ground-state destabilization of the N-C(O) linkage represents a powerful tool to functionalize the historically inert amide bond. This burgeoning reaction manifold relies on the availability of amide bond precursors that participate in weakening of the nN → π*C=O conjugation through N-C twisting, N pyramidalization, and nN electronic delocalization. Since 2015, acyl N-C amide bond activation through ground-state destabilization of the amide bond has been achieved by transition-metal-catalyzed oxidative addition of the N-C(O) bond, generation of acyl radicals, and transition-metal-free acyl addition. This Perspective summarizes contributions of our laboratory in the development of new ground-state-destabilized amide precursors enabled by twist and electronic activation of the amide bond and synthetic utility of ground-state-destabilized amides in cross-coupling reactions and acyl addition reactions. The use of ground-state-destabilized amides as electrophiles enables a plethora of previously unknown transformations of the amide bond, such as acyl coupling, decarbonylative coupling, radical coupling, and transition-metal-free coupling to forge new C-C, C-N, C-O, C-S, C-P, and C-B bonds. Structural studies of activated amides and catalytic systems developed in the past decade enable the view of the amide bond to change from the "traditionally inert" to "readily modifiable" functional group with a continuum of reactivity dictated by ground-state destabilization.

Amide N-C Bond Activation: A Graphical Overview of Acyl and Decarbonylative Coupling

This Graphical Review provides an overview of amide bond activation achieved by selective oxidative addition of the N-C(O) acyl bond to transition metals and nucleophilic acyl addition, resulting in acyl and decarbonylative coupling together with key mechanistic details pertaining to amide bond distortion underlying this reactivity manifold.

Bulky Pd-PEPPSI-Embedded Conjugated Microporous Polymers-Catalyzed Suzuki-Miyaura Cross-Coupling of Aryl Chlorides and Arylboronic Acids

Through post-synthesis method, a type of bulky N-heterocyclic carbenes (NHCs) functionalized conjugated microporous polymers to supported the palladium-based molecular catalyst has been developed. The resulting heterogeneous catalyst Pd-PEPPSI-CMP, showing greater...

Evaluation of Cyclic Amides as Activating Groups in N-C Bond Cross-Coupling: Discovery of N-Acyl-δ-valerolactams as Effective Twisted Amide Precursors for Cross-Coupling Reactions

The development of efficient methods for facilitating N-C(O) bond activation in amides is an important objective in organic synthesis that permits the manipulation of the traditionally unreactive amide bonds. Herein, we report a comparative evaluation of a series of cyclic amides as activating groups in amide N-C(O) bond cross-coupling. Evaluation of N-acyl-imides, N-acyl-lactams, and N-acyl-oxazolidinones bearing five- and six-membered rings using Pd(II)-NHC and Pd-phosphine systems reveals the relative reactivity order of N-activating groups in Suzuki-Miyaura cross-coupling. The reactivity of activated phenolic esters and thioesters is evaluated for comparison in O-C(O) and S-C(O) cross-coupling under the same reaction conditions. Most notably, the study reveals N-acyl-δ-valerolactams as a highly effective class of mono-N-acyl-activated amide precursors in cross-coupling. The X-ray structure of the model N-acyl-δ-valerolactam is characterized by an additive Winkler-Dunitz distortion parameter Σ(τ+χ_N) of 54.0°, placing this amide in a medium distortion range of twisted amides. Computational studies provide insight into the structural and energetic parameters of the amide bond, including amidic resonance, N/O-protonation aptitude, and the rotational barrier around the N-C(O) axis. This class of N-acyl-lactams will be a valuable addition to the growing portfolio of amide electrophiles for cross-coupling reactions by acyl-metal intermediates.

Evidence for “cocktail”-type catalysis in Buchwald–Hartwig reaction. A mechanistic study

The mechanism of the C–N cross-coupling reaction, catalyzed by Pd/NHC, was evaluated at the molecular and nanoscale levels. The first evidence for the involvement of a “cocktail”-type system in the Buchwald–Hartwig reaction is provided.