Ruthenium-catalyzed Asymmetric Dehydrative Allylic Cyclization of Chalcogen 5-Membered Heteroaromatics

The asymmetric dehydrative intramolecular allylation reactions of furan and thiophene were performed using a cationic cyclopentadienyl-ruthenium (CpRu) complex of a chiral pyridine carboxylic acid, namely Cl-Naph-PyCOOH. Both furan and thiophene tethered with an allylic alcohol gave the corresponding bicyclic compounds in high yields and enantioselectivities using 0.1–5 mol% of catalyst. The reaction was found to proceed via a similar enantioface selection method mechanism to that previously reported by our group, which involved halogen and hydrogen bond formation, in addition to the generation of an intermediate σ-allyl complex.

Highly Enantioselective Synthesis of Indazoles with a C3-Quaternary Chiral Center Using CuH Catalysis

<div><div><div><p>C3-substituted 1H-indazoles are useful and important substructures in many pharmaceuticals. Methods for direct C3- functionalization of indazoles are relatively rare, compared to reactions developed for the more nucleophilic N1 and N2 positions. Herein, we report a highly C3-selective allylation reaction of 1H-N-(benzoyloxy)indazoles using CuH catalysis. A variety of C3-allyl 1H-indazoles with quaternary stereocenters were efficiently prepared with high levels of enantioselectivity. Density functional theory (DFT) calculations suggest that the indazole addition to copper allyl complex proceeds through an enantioselectivity-determining six- membered Zimmerman-Traxler-type transition state. The enantioselectivity is governed both by the ligand-substrate steric interac- tions and the steric repulsions with the pseudoaxial substituent in the six-membered allylation transition state.</p></div></div></div>

Highly Enantioselective Synthesis of Indazoles with a C3-Quaternary Chiral Center Using CuH Catalysis

<div><div><div><p>C3-substituted 1H-indazoles are useful and important substructures in many pharmaceuticals. Methods for direct C3- functionalization of indazoles are relatively rare, compared to reactions developed for the more nucleophilic N1 and N2 positions. Herein, we report a highly C3-selective allylation reaction of 1H-N-(benzoyloxy)indazoles using CuH catalysis. A variety of C3-allyl 1H-indazoles with quaternary stereocenters were efficiently prepared with high levels of enantioselectivity. Density functional theory (DFT) calculations suggest that the indazole addition to copper allyl complex proceeds through an enantioselectivity-determining six- membered Zimmerman-Traxler-type transition state. The enantioselectivity is governed both by the ligand-substrate steric interac- tions and the steric repulsions with the pseudoaxial substituent in the six-membered allylation transition state.</p></div></div></div>

The Mechanism of Rhodium Catalyzed Allylic C–H Amination

The mechanism of catalytic allylic C–H amination reactions promoted by Cp*Rh complexes is reported. Reaction kinetics experiments, stoichiometric studies, and DFT calculations demonstrate that allylic C–H activation to generate a Cp*Rh(π-allyl) complex is viable under mild reaction conditions. The role of external oxidant in the catalytic cycle is elucidated. Quantum mechanical calculations, stoichiometric reactions, and cyclic voltammetry<b></b>experiments support an oxidatively induced reductive elimination process of the allyl fragment with an acetate ligand. Lastly, evidences supporting the amination of an allylic acetate intermediate is presented. Both nucleophilic substitution catalyzed by Ag⁺that behaves as a Lewis acid catalyst and an inner-sphere amination catalyzed by Cp*Rh are shown to be viable for the last step of the allylic amination reaction.