CATALYTIC ASYMMETRIC C-C BOND-FORMING REACTION USING OPTICALLY-ACTIVE RARE-EARTH COMPLEX

Newly synthesized optically active rare earth complexes made possible a catalytic asymmetric nitroaldol reaction for the first time, giving nitroaldols in up to 95% ee. The catalyst complexes were prepared from rare earth (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, and Y) trichloride, dilithium (S)-binaphthoxide, NaOH, and H2O. The presence of LiCl and H2O appeared to be essential to obtain nitroaldols of high optical purity. The application to catalytic asymmetric syntheses of beta-blockers, (S)-metoprolol and (S)-propranolol, has been also achieved. Laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) of rare earth metal BINOL complexes has suggested that all complexes are possessing one rare earth atom, three BINOL units and three Li atoms. Finally, X-ray crystallographic analyses of the Li free (Na containing) rare earth BINOL complexes (Pr, Nd and Eu) have been performed and the results were very much in agreement with the spectroscopic and analytical data. Although every Li free catalyst was not effective for asymmetric nitroaldol reactions, an addition of three molar equivalents of LiCl caused complete exchange of Na with Li resulting in the formation of an effective asymmetric catalyst.