Enantioselective addition of diethylzinc to aldehydes using immobilized chiral BINOL–Ti complex on ordered mesoporous silicas

A chiral (S)-BINOL ligand has been covalently grafted on ordered mesoporous silicas—MCM-41 and SBA-15 and the resulting inorganic–organic hybrid materials used as chiral auxiliaries in Ti-promoted enantioselective addition of diethyl zinc to aldehydes under heterogeneous conditions. These heterogeneous catalysts showed promising activity and enantioselectivity. The catalyst having a larger pore diameter with capping of free silanol moiety with trimethylsilyl (TMS) group was found to be more active with enantioselectivities up to 81% being achieved. The catalyst worked well up to three cycles with retention of enantioselectivity after washing with 10% HCl in methanol.

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(S)-2-Hydroxy-2′-pivaloyloxy-1,1′-binaphthylC24H22O3[α]D25=-54.5 (c 0.5, THF)Source of chirality: (S)-2,2′-dihydroxy-1,1′-binaphthylAbsolute configuration: (S)

(S)-6-Bromo-2-hydroxy-2′-pivaloyloxy-1,1′-binaphthylC24H21O3Br[α]D25=+6.0 (c 0.52, THF)Source of chirality: (S)-2,2′-dihydroxy-1,1′-binaphthylAbsolute configuration: (S)

(S)-6-Bromo-2,2′-dihydroxy-1,1′-binaphthylC20H13O2Br[α]D25=+6.35 (c 0.55, THF)Source of chirality: (S)-2,2′-dihydroxy-1,1′-binaphthylAbsolute configuration: (S)

(S)-6-Bromo-2,2′-dimethoxy-1,1′-binaphthylC22O17O2Br[α]D25=+48.1 (c 0.5, CHCl3)Source of chirality: (S)-2,2′-dihydroxy-1,1′-binaphthylAbsolute configuration: (S)