Palladium-Catalyzed Site-Selective [5 + 1] Annulation of Aromatic Amides with Alkenes: Acceleration of β-Hydride Elimination by Maleic Anhydride from Palladacycle

Merging directed sp3 and nondirected sp2 C-H functionalization for Pd-catalyzed polydeuteration of (hetero)arenes

Polydeuteration has emerged as a key strategy in the development of pharmaceuticals and functional organic materials, advancing beyond monodeuteration and trideuteromethylation. We have developed methods for the polydeuteration of a wide range of organic compounds through Pd-catalyzed directed sp3 C-H activation and nondirected sp2 C-H activation, using readily available deuterium source, AcOH-d 4. This approach addresses the challenge of facilitating both directed and nondirected C-H functionalization of electronically and sterically diverse (hetero)aromatic compounds through the use of a versatile [2,2'-bipyridin]-6(1H)-one (BpyOH) ligand. This method demonstrates high functional group compatibility, readily applicable in the presence of directing functional groups such as carboxylic acids, amides, and azoles, as well as nondirecting electron-withdrawing groups such as nitro, sulfonamide, and ester groups. DFT calculations reveal that ligands influence intermediates and transition states by providing bidentate chelation, internal base, and hydrogen bonding. The Pd(BpyOH) complex exhibits well-balanced reactivity for C-H cleavage while readily forming complexes with substrates, which is relevant to other Pd-catalyzed C-H functionalization reactions. Our approach significantly broadens the scope of deuterated building blocks and late-stage deuteration, thereby facilitating evaluation of the deuterium effect in various applications across medicinal chemistry, materials science, and beyond.

Computational Insights into Palladium-Catalyzed Site-Selective Anilide and Benzamide-Type [3+2] Annulation via Double C-H Bond Activation

The mechanism of palladium-catalyzed annulation reactions of benzamide- and anilide-type aromatic systems with maleimides is investigated using density functional theory. Double C-H bond activation is key to forming the desired annulation product. The first C-H bond activation for anilide- and amide-type ligands can occur at the ortho and benzylic C-H bonds, while the second C-H activation occurs at the meta carbon of the aromatic rings. For the anilide-type system, ortho and benzylic C-H bond activations occur via four- and five-membered palladacycles, respectively. In contrast, for the benzamide-type system, ortho and benzylic C-H bond activations occur via five- and six-membered palladacycles, respectively. The energy span model suggests that the initial C-H bond activation step at the benzylic position determines the turnover frequency for both anilide- and benzamide-type systems. Energy decomposition analysis and distortion-interaction/activation-strain analyses are employed to understand the electronic and steric factors controlling the turnover frequency-determining transition state.

Palladium-Catalyzed Selective Benzylic C-H Alkylation of Aromatic Sulfonamides with Maleimides

An efficient method for the selective benzylic C-H alkylation of sulfonamides using maleimides has been developed. The reaction proceeds via the benzylic C(sp3)-H bond activation of sulfonamide in the presence of a Pd(II) catalyst without requiring any oxidant, additive, or external ligand. This methodology is highly compatible with a wide variety of substituted maleimides. A plausible reaction mechanism is also proposed to account for this alkylation reaction.

Palladium-Catalyzed [3 + 2] Annulation of Aromatic Amides with Maleimides through Dual C-H Activation

A palladium-catalyzed [3 + 2] annulation of substituted aromatic amides with maleimides providing tricyclic heterocyclic molecules in good to moderate yields through weak carbonyl chelation is reported. The reaction proceeds via a dual C-H bond activation where the first C-H activation takes place selectively at the benzylic position followed by a second C-H bond activation at the meta position to afford a five-membered cyclic ring. An external ligand Ac-Gly-OH has been used to succeed in this protocol. A plausible reaction mechanism has been proposed for the [3 + 2] annulation reaction.