Multiplicative enhancement of stereoenrichment by a single catalyst for deracemization of alcohols.

Stereochemical enrichment of a racemic mixture by deracemization must overcome unfavorable entropic effects as well as the principle of microscopic reversibility; recently, photochemical reaction pathways unveiled by the energetic input of light have led to innovations toward this end, most often by ablation of a stereogenic C(sp)-H bond. We report a photochemically driven deracemization protocol in which a single chiral catalyst effects two mechanistically different steps, C-C bond cleavage and C-C bond formation, to achieve multiplicative enhancement of stereoinduction, which leads to high levels of stereoselectivity. Ligand-to-metal charge transfer excitation of a titanium catalyst coordinated by a chiral phosphoric acid or bisoxazoline efficiently enriches racemic alcohols that feature adjacent and fully substituted stereogenic centers to enantiomeric ratios up to 99:1.

Alkoxy Radicals See the Light: New Paradigms of Photochemical Synthesis.

Alkoxy radicals are highly reactive species that have long been recognized as versatile intermediates in organic synthesis. However, their development has long been impeded due to a lack of convenient methods for their generation. Thanks to advances in photoredox catalysis, enabling facile access to alkoxy radicals from bench-stable precursors and free alcohols under mild conditions, research interest in this field has been renewed.

CuCl-catalyzed highly stereoselective and chemoselective reduction of alkynyl amides into α,β-unsaturated amides using silanes as hydrogen donors.

A CuH-catalyzed Z-selective partial reduction of alkynyl amides to afford α,β-unsaturated amides using silane as the hydrogen donor is developed. This reaction is carried out under mild conditions and able to accommodate a broad scope of alkynyl amides including those bearing a terminal carbon-carbon double bond or triple bond, affording alkenyl amides with high stereoselectivity and excellent yields.

CuH-Catalyzed Synthesis of 3-Hydroxyindolines and 2-Aryl-3H-indol-3-ones from -Alkynylnitroarenes, Using Nitro as Both the Nitrogen and Oxygen Source.

CuH-catalyzed diasterospecific synthesis of 3-hydroxyindolines and 2-aryl-3H-indol-3-ones have been developed from -alkynylnitroarenes in the presence of hydrosilane as the reductant. The protocol employs nitro as both nitrogen and oxygen sources for the intramolecular simultaneous construction of C-N and C-O bonds.