Ruthenium(0)-Catalyzed [4+2] Cycloaddition of Acetylenic Aldehydes with α-Ketols: Convergent Construction of Angucycline Ring Systems.

Ruthenium(0) complexes modified by CyJohnPhos or RuPhos catalyze the successive C-C coupling of acetylenic aldehydes with α-ketols to form [4+2] cycloadducts as single diastereomers. This method enables convergent construction of type II polyketide ring systems of the angucycline class.

Ruthenium(0) Catalyzed Endiyne-α-Ketol [4 + 2] Cycloaddition: Convergent Assembly of Type II Polyketide Substructures via C-C Bond Forming Transfer Hydrogenation.

Upon exposure of 3,4-benzannulated 1,5-diynes (benzo-endiynes) to α-ketols (α-hydroxyketones) in the presence of Ru(0) catalysts derived from Ru3(CO)12 and RuPhos or CyJohnPhos, successive redox-triggered C-C coupling occurs to generate products of [4 + 2] cycloaddition. The proposed catalytic mechanism involves consecutive alkyne-carbonyl oxidative couplings to form transient oxaruthanacycles that suffer α-ketol mediated transfer hydrogenolysis. This process provides a new, convergent means of assembling Type II polyketide substructures.

Enantioselective copper-catalyzed reductive coupling of alkenylazaarenes with ketones.

Catalytic enantioselective methods for the preparation of chiral azaarene-containing compounds are of high value. By combining the utility of copper hydride catalysis with the ability of C═N-containing azaarenes to activate adjacent alkenes toward nucleophilic additions, the enantioselective reductive coupling of alkenylazaarenes with ketones has been developed. The process is tolerant of a wide variety of azaarenes and ketones, and provides aromatic heterocycles bearing tertiary-alcohol-containing side chains with high levels of diastereo- and enantioselection.

Aromatic heterocycles as activating groups for asymmetric conjugate addition reactions. Enantioselective copper-catalyzed reduction of 2-alkenylheteroarenes.

The versatility of chiral copper hydride catalysis has been demonstrated through development of highly enantioselective 1,4-reductions of 2-alkenylheteroarenes, substrates that have been rarely considered for asymmetric conjugate addition reactions. Both azoles and azines serve as efficient activating groups for this process.