Organocatalytic Asymmetric Michael Addition of 5H-Oxazol-4-ones to Nitroolefins
摘要:
The first organocatalytic asymmetric Michael addition of 5H-oxazol-4-ones to nitroolefins has been developed. In the presence of easily prepared L-tert-leucine-derived tertiary amine/thiourea catalyst, the Michael addition of 5H-oxazol-4-ones to nitroolefins proceeded in an excellent diastereo- and enantioselective manner (up to 99% ee and >19:1 dr). The Michael adducts obtained are valuable precursors for the synthesis of chiral alpha-alkyl-alpha-hydroxy carboxylic acid derivatives, which represent a series of versatile building blocks in many biologically active compounds.
Enantioselective Synthesis of Coumarins Catalyzed by a Bifunctional Amine-Thiourea Catalyst
作者:Yaojun Gao、Qiao Ren、Lei Wang、Jian Wang
DOI:10.1002/chem.201002202
日期:2010.11.22
Efficient excess: An efficient and facile enantioselective Michael addition reaction through hydrogen‐bonding catalysis for the synthesis of coumarin complexes has been developed (see scheme). A simple bifunctional amine–thiourea small molecule has been discovered to catalyze this process with high yields and high to excellent enantiomeric excesses.
the presence of an L-tert-leucine-derived urea–ammonium salt as phase-transfer catalyst, a highly enantioselective alkylation of 5H-oxazol-4-ones with various benzyl bromides and allylic bromides has been developed to furnish catalytic asymmetric synthesis of biologically important dialkylated α-hydroxy carboxylic acids with a broad scope. This is the first example of an L-amino acid-derived urea–ammonium