Heterogeneous asymmetric Henry reaction using a chiral bis(oxazoline)-copper complex immobilized on magnetically separable mesocellular mesoporous silica support

A chiral bis(oxazoline) ligand was immobilized onto a magnetically separable hierarchically-ordered mesocellular mesoporous silica (M-HMMS) and this new catalytic system was examined in the asymmetric Henry reaction between various aldehydes and nitromethane at ambient temperature. Good enantioselectivity (upto 86.0% ee) was observed when the free silanol groups of the mesoporous silica were capped by trimethylsilyl group. This catalyst was separated magnetically and reused several times without significant loss of reactivity or enantioselectivity. This magnetic separation of catalysts could lead to further development toward practical industrial scale application due to simplicity without cumbersome filtration.

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2,2-Bis((3aS,8aR)-8,8a-dihydro-3aH-indeno[1,2-d]oxazol-2-yl)propane-1,3-diyl bis(6-azidohexanoate)C35H40N8O6[α]D23=-127.7 (c 1.0, EtOH)Source of chirality: [3aS-[2(3′aR∗,8′aS∗),3′aα,8′aα]]-(−)-2,2′-methylenebis[3a,8a-dihydro-8H-indeno[1,2-d]oxazole]Absolute configuration: (3aS,8aR)