Highly enantioselective titanium-catalyzed cyanation of imines at room temperature.

A highly active and enantioselective titanium-catalyzed cyanation of imines at room temperature is described. The catalyst used is a partially hydrolyzed titanium alkoxide (PHTA) precatalyst together with a readily available N-salicyl-beta-aminoalcohol ligand. Up to 98% ee was obtained with quantitative yields in 15 min of reaction time using 5 mol % of the catalyst.

The reactive intermediate of catalytic borohydride reduction by Schiff base-cobalt complexes.

The key reactive intermediate of borohydride reduction catalyzed by Schiff base-cobalt complexes is proposed to be the dichloromethylcobalt hydride with a sodium cation, based on experimental and theoretical studies. It was revealed that chloroform is not the solvent but the reactant that activates the cobalt catalyst. The substrate carbonyl compounds are fixed and activated by the alkali cation, which is captured by the oxygen atoms of the planar ligand and the chlorine atom of the axial ligand, and attacked by the hydride on the cobalt atom via a six-membered-like transition state to afford the corresponding alcohol.

Enantioselective borohydride reduction catalyzed by optically active cobalt complexes.

The highly enantioselective borohydride reduction of aromatic ketones or imines to the corresponding alcohols was developed in the presence of a catalytic amount of an optically active cobalt(II) complex catalyst. This enantioselective reduction is carried out using a precisely premodified borohydride with alcohols such as tetrahydrofurfuryl alcohol, ethanol and methanol. High optical yields are obtained by choosing the appropriate alcohol as modifiers and a suitable beta-ketoiminato ligand of the catalyst.