Enantioselective conjugate addition of primary dialkylzinc reagents to 2-aryl- and 2-heteroaryl-nitroolefins mediated by titanium-TADDOLates preparation of enantioenriched 2-aryl-alkylamines
摘要:
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).
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).
Nonreductive Enantioselective Ring Opening of<i>N</i>-(Methylsulfonyl)dicarboximides with Diisopropoxytitanium α,α,α′,α′-Tetraaryl-1,3-dioxolane-4,5-dimethanolate
作者:Diego J. Ramón、Gabriela Guillena、Dieter Seebach
DOI:10.1002/hlca.19960790328
日期:1996.5.8
dicarboximides 1a–f are converted enantioselectively to isopropyl [(sulfonamido)carbonyl]-carboxylates 2a–f by diisopropoxytitaniumTADDOLate (75–92% yield; see Scheme 3). The enantiomer ratios of the products are between 86:14 and 97:3, and recrystallization from CH2Cl2/hexane leads to enantiomerically pure sulfonamido esters 2 (Scheme 3). The enantioselectivity shows a linear relationship with the