Enantioselective Additions of Aryltitanium Tris(isopropoxide) to Ketones: Structure of [(i-PrO)2Ti{μ-(S)-BINOLate}(μ-O-i-Pr)TiPh(O-i-Pr)2], Study of Mechanistic and Stereochemical Insights

Aryl addition reactions of ArTi(O-i-Pr)3 to aromatic, heteroaromatic, or ,-unsaturated ketones are described, producing tertiary alcohols in good to excellent enantioselectivities of up to 97% ee. The structure of the dititanium complex [(i-PrO)2Ti{-(S)-BINOLate}(-O-i-Pr)TiPh(O-i-Pr)2] [(S)-4] that simultaneously bears a chiral directing ligand and a nucleophile is reported. Complex (S)-4 possesses a pocket structure and has been illustrated as the key active species for addition reactions of both aldehydes and ketones. Mechanistic and stereochemical insights concerning addition reactions of organometallic reagents to organic carbonyls are rationalized based on the pocket structure and pocket size of (S)-4.