A Lewis Acid-Controlled Enantiodivergent Epoxidation of Aldehydes.

Two epoxidation catalysts, one of which consists of two VANOL ligands and an aluminum and the other that consists of two VANOL ligands and a boron, were compared. Both catalysts are highly effective in the catalytic asymmetric epoxidation of a variety of aromatic and aliphatic aldehydes with diazoacetamides, giving high yields and excellent asymmetric inductions. The aluminum catalyst is effective at 0 °C and the boron catalyst at -40 °C.

Copper-Catalyzed Hydroamination: Enantioselective Addition of Pyrazoles to Cyclopropenes.

Chiral -cyclopropyl pyrazoles and structurally related heterocycles are prepared using an earth-abundant copper catalyst under mild reaction conditions with high regio-, diastereo-, and enantiocontrol. The observed N:N regioselectivity favors the more hindered nitrogen of the pyrazole. Experimental and DFT studies support a unique mechanism that features a five-centered aminocupration.

Copper-Phosphido Catalysis: Enantioselective Addition of Phosphines to Cyclopropenes.

We describe a copper catalyst that promotes the addition of phosphines to cyclopropenes at ambient temperature. A range of cyclopropylphosphines bearing different steric and electronic properties can now be accessed in high yields and enantioselectivities. Enrichment of phosphorus stereocenters is also demonstrated via a Dynamic Kinetic Asymmetric Transformation (DyKAT) process.

Probing the Free Energy Landscape of Organophotoredox-Catalyzed Anti-Markovnikov Hydrofunctionalization of Alkenes.

Experimental C kinetic isotope effects (KIEs) provide unprecedented mechanistic insight into three intermolecular anti-Markovnikov alkene hydrofunctionalization reactions─hydroesterification, hydroamination, and hydroetherification─enabled by organophotoredox catalysis. All three reactions are found to proceed via initial oxidation of the model alkenes to form a radical cation intermediate, followed by sequential nucleophilic attack and hydrogen-atom transfer to deliver the hydrofunctionalized product. A normal C KIE on the olefinic carbon that undergoes nucleophilic attack provides qualitative evidence for rate-limiting nucleophilic attack in all three reactions.