Mesoporous Silica Supported BINOL-Ti for Addition of Et₂Zn to Aldehydes

Significance

Mesoporous silica supported(S)-BINOLs were prepared and used as chiral ligands in Ti-promoted enantioselective addition of Et₂Zn to aldehydes. The mesoporous silica supported BINOLs 1a and 1b were prepared from 6-substituted BINOL derivative and MCM-41 or SBA-15 (eq. 1). Trimethylsilyl-capped mesoporous silica supported BINOLs 1c and 1d were also prepared in a similar manner (eq. 2). The addition of Et₂Zn to the aldehydes took place in the presence of Ti(Oi-Pr)₄ and the mesoporous silica supported BINOL ligands 1 to give the alcohols in 76-98% yield with 37-81% ee (eq. 3). Of all tested catalysts, the Ti complex with the trimethylsilyl-capped SBA-15-supported BINOL 1d-Ti showed the highest enantioselectivity. The catalyst 1d-Ti was reused twice without significant loss of catalytic activity and selectivity [85% yield, 80% ee (1st reuse), 77% yield, 78% ee (2nd reuse)].