Chiral borane of layered α-Zirconium-N-(m-solfophenyl)-L-Valine-Phosphonate Methanphosphonate promoters for the asymmetric Mukaiyama Aldol reaction

Several α-Zr[O3PC6H4SO2NHCH(CH(CH3)2)COOH)]2-x(O3PCH3)x·nH2O samples, containing chiral pendent groups, were prepared by allowing Zr fluoro complexes to decompose in the presence of N-(m-solfophenyl)-l(+)-Valine-phosphonic (PVal) and methanphosphonic (PMe) acids. The layered compounds were characterized by different techniques and left to react with BH3·THF reagent to obtain heterogeneous chiral oxazaborolidinone. These materials were found to be efficient catalysts of the typical asymmetric Mukaiyama Aldol reaction of 1-methoxy-2-methyl-1-trimethylsiloxy-1-propene and benzaldehyde in CH2Cl2 and THF at 0 °C, with enantiomeric excess up to 50%.