Application of the Chiral Bis(phosphine) Monoxide Ligand to Catalytic Enantioselective Addition of Dialkylzinc Reagents to β-Nitroalkenes
作者:Alexandre Côté,、Vincent N. G. Lindsay、André B. Charette
DOI:10.1021/ol062792t
日期:2007.1.1
see text] Me-DuPHOS monoxide is shown to be a very effective ligand in the enantioselective copper-catalyzed addition of dialkylzincreagents to beta-nitroalkenes providing access to chiral nitroalkanes. The major advantages of this process are high yields, broad and complementary substrate scope, and high enantioselectivities. The effect of achiral dummy ligands as an additive has also been documented
Enantioselective conjugate addition of primary dialkylzinc reagents to 2-aryl- and 2-heteroaryl-nitroolefins mediated by titanium-TADDOLates preparation of enantioenriched 2-aryl-alkylamines
作者:Harald Schäfer、Dieter Seebach
DOI:10.1016/0040-4020(94)01100-e
日期:1995.2
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).