The nanocomposites of SO₃H-hollow-nanosphere and chiral amine for asymmetric aldol reaction

The nanocomposites formed by SO₃H-hollow-nanospheres and chiral amines are highly efficient catalysts for the direct asymmetric aldol reaction of cyclohexanone and 4-nitrobenzaldehyde. The catalyst showed 91% yield with 96% ee under optimized reaction conditions. SO₃H-hollow-nanospheres were synthesized by oxidation of thiol-hollow-nanospheres, which were fabricated through a one-pot co-condensation of 1,2-bis(trimethoxysilyl)ethane and 3-mercaptopropyltrimethoxysilane around F127 micelles in the presence of NaOAc. Chiral amines could be combined with SO₃H-hollow-nanospheres through facile electrostatic interactions. The obtained nanocomposites showed a much higher reaction rate than the catalyst formed from the combination of chiral amine and SO₃H-mesoporous-organosilica (ribbon shaped particles with particle size of tens of micrometres) in the direct asymmetric aldol reaction. This is mainly attributed to the hollow spherical morphology and nano-scale particle size (16-20 nm) of the SO₃H-hollow-nanospheres.