Synthesis of novel chiral Schiff-base ligands and their application in asymmetric nitro aldol (Henry) reaction

Chiral Schiff-bases prepared from chiral amino alcohols catalyze the enantioselective Henry (nitro aldol) reaction between nitromethane and p-nitrobenzaldehyde in the presence of Cu(OTf)2 and Zn(OTf)2. Zn(OTf)2 promoted the reaction yield, while Cu(OTf)2 promoted the enantiomeric excess. The highest enantioselectivities were observed with ligand 3 (44% ee) and ligand 5 (47% ee).

Figure optionsDownload as PowerPoint slide

C46H44N2O5[α]D20=+12.2 (c 2, CH2Cl2)Source of chirality: (1S,2R)-2-amino-1,2-diphenylethanolAbsolute configuration: (S,R,S,R)

C34H36N2O5[α]D20=+103.2 (c 2, CH2Cl2)Source of chirality: (R)-(−)-phenylglycinolAbsolute configuration: (R,R)

C50H44N2O4[α]D20=+50 (c 2, CH2Cl2)Source of chirality: (1S,2R)-2-amino-1,2-diphenylethanolAbsolute configuration: (S,R,S,R)

C38H36N2O4[α]D20=+102.9 (c 2, CH2Cl2)Source of chirality: (R)-(−)-phenylglycinolAbsolute configuration: (R,R)