Carboxylate-Assisted Iridium (III)-Catalyzed C(sp2)-H Amidation of 2-Aroylimidazoles With Dioxazolones

"On Water" Cationic Ruthenium(II) Catalysed Direct Aryl C(sp2)-H Amidation of Biorelevant Heterocyclic Scaffolds

Ru(II)-Catalyzed "On Water" direct aryl C(sp2)-H amidation of 2-arylbenzo[d]-thiazole/oxazole with acyl azide is reported under silver-free condition. Deuterium scrambling experiments suggested reversible C-H activation catalyzed by active cationic ruthenium species. The organic solvents such as DCE, DMF, DMSO, MeCN, dioxane, and PhMe were not conducive for the C-H amidation except for PhCl in which case, however, inferior yield (31 %) was obtained. Water plays critical roles (i) during the formation of active cationic Ru-species, (ii) as proton scavenger during ligand-assisted C-H activation through hydrogen bond formation as evidenced by solvent kinetic isotope effect, and (iii) in the final protodissociation step. The mechanistic proposal resembles secondary coordination sphere hydrogen bond controlled transition metal catalysis showcasing the aryl C-H amidation through outer sphere nitrene insertion. The "on water" aryl C-H amidation protocol showed wide substrate scope with respect to the 2-arylbenzo[d]-thiazole/oxazole scaffold as well as the aryl moiety of the aroyl azide. While the applicability of the Ru(II)-catalysed "on water" C-H amidation protocol to 2-arylbenzo[d]-thiazole and 2-arylbenzo[d]-oxazole demonstrates its scope with respect to the directing group the effectiveness for sulfonamidation and phosphoramidation further broaden the synthetic scope.

Comprehensive Theoretical Study of Cp*IrIII-Catalyzed Intermolecular Enantioselective Allylic C-H Amidation: Reaction Mechanism, Electronic Processes, and Regioselectivity

Density functional theory was used to elucidate the reaction mechanism of Cp*Ir^III-catalyzed intermolecular regioselective C(sp³)-H amidation of alkenes with methyl dioxazolones. All substrates, intermediates, and transition states were fully optimized at the ωB97XD/6-31G(d,p) level (LANL2DZ(f) for Ir). The computational results revealed that this amidation occurred through the Ir^III/Ir^V catalytic cycle, involving four important elementary steps: C-H bond activation, oxidative addition of methyl dioxazolone, reductive elimination, and proto-demetalation, and the first was the rate-determining step. The C-H bond activation showed good α- and branch-regioselectivity, decided by the distortion energy of 2-pentene and the interaction energy of the transition state, respectively. The oxidative addition of dioxazolone occurred in one elementary step with CO₂ disassociation. The reductive elimination showed good branch-regioselectivity determined by the distorted energy of the allyl group. In the proto-demetalation, hydrogen directly transferred from the oxygen atom to the nitrogen atom. Moreover, to clarify the effect of the substituted groups, selected 12 substrates were also discussed in this text.