Intermolecular Palladium(0)-Catalyzed Atropo-enantioselective C-H Arylation of Heteroarenes.

Atropisomeric (hetero)biaryls are motifs with increasing significance in ligands, natural products, and biologically active molecules. The straightforward construction of the stereogenic axis by efficient C-H functionalization methods is extremely rare and challenging. An intermolecular and highly enantioselective C-H arylation of relevant heteroarenes providing an efficient access to atropisomeric (hetero)biaryls is reported. The use of a Pd(0) complex equipped with H8-BINAPO as a chiral ligand enables the direct functionalization of a broad range of 1,2,3-triazoles and pyrazoles in excellent yields and selectivities of up to 97.5:2.5 er. The method also allows for an atroposelective double C-H arylation for the construction of two stereogenic axes with >99.5:0.5 er.

Pd-catalyzed γ-arylation of γ,δ-unsaturated O-carbamates via an unusual haptotropic rearrangement.

An unusual γ-selectivity was observed in the arylation of γ,δ-unsaturated O-carbamates involving directed lithiation, transmetallation to zinc and Negishi coupling, when a specific combination of aryl electrophile and phosphine ligand is employed. Mechanistic studies indicate that an unusual, stereospecific haptotropic rearrangement of the palladium-diene intermediate is involved.

Enantioselective α-Arylation of O-Carbamates via Sparteine-Mediated Lithiation and Negishi Cross-Coupling.

A general and highly enantioselective arylation of carbamates derived from primary alcohols was developed by combining Hoppe's sparteine-mediated asymmetric lithiation with Negishi cross-coupling. Coupled with Aggarwal's lithiation-borylation sequence, the current method provides a short and divergent access to a variety of enantioenriched secondary and tertiary benzylic alcohols.