ENANTIOSELECTIVE CONJUGATE ADDITION OF PRIMARY DIALKYLZINC REAGENTS TO 2-ARYL- AND 2-HETEROARYL-NITROOLEFINS MEDIATED BY TITANIUM-TADDOLATES PREPARATION OF ENANTIOENRICHED 2-ARYL-ALKYLAMINES

The addition of dialkylzinc to nitroolefins is catalyzed by Lewis acids such as MgBr2, MgI2, and chlorotitanates. Using the (R,R)-Ti-TADDOLates the addition of diethyl-, dibutyl-, and dioctyl zinc to 2-aryl-nitroethenes is shown to be enantioselective with yields near 90% and enantiomer ratios of ca. 9:1 (products 3-12; enantiomer enrichment by crystallization is possible in some cases). Reduction of the 2-aryl-nitroalkanes thus obtained by catalytic hydrogenation over Pd/C or Raney-Ni leads to the corresponding enantioenriched 2-aryl-alkylamines (products 13-21). The enantiopurity of the nitroalkanes and amines was determined by chromatography on chiral columns. The configuration of the products is assigned (S) by optical comparison and by analogy (comparison of five different types of physical data). The relative topicity of the process is unlike (ul = R,R/Si or S,S/Re).