Lanthanide (III) salt complexes: arrayed acid-base networks for enantioselective catalysis. The nitroaldol reaction upon aldehydes and trifluoromethylketones.
Shelf stable, chiral-at-metal, D(3) symmetric, 3:1 complexes of lanthanide (III) triflate salts are easily available by complexation with binolam (3,3'-diethylaminomethyl-2,2'-dihydroxy-1,1'-dinaphthalene) 1 or binolamo (3,3'-diethylaminooxymethyl-2,2'-dihydroxy-1,1'-dinaphthalene) 2 ligands. The resulting compounds 3Ln and 4Ln are isostructural, as demonstrated by their spectroscopic data, and possess an arrayed acid-base LABABB network. Complexes are kinetically labile, and in solution undergo hydrolysis by water. The lanthanum complex derived from binolam, i.e., (Delta,S,S,S)- (binolam)(3).la(OTf)(3)3La was found to be the most active catalyst in promoting direct nitroaldol reactions upon aldehydes and trifluoromethyl ketones, thereby giving rise to secondary nitroalcohols and tertiary alpha-trifluoromethyl-beta-nitroalcohols, respectively, with high ee in both cases. Enantiomerically enriched tertiary nitroalcohols were easily reduced to the corresponding aminoalcohols having a quaternary asymmetric carbon without loss of enantiomeric purity.
Saá
José M
JM
Departament de Química, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain. jmsaa@uib.es
Tur
Fernando
F
González
José
J