Highly Enantioselective Chlorination of β-Keto Esters and Subsequent SN2 Displacement of Tertiary Chlorides: A Flexible Method for the Construction of Quaternary Stereogenic Centers
摘要:
Highly enantioselective chlorination of beta-oxo esters and subsequent stereospecific substitution of tertiary chlorides are described. Enantioselective chlorination of beta-keto esters and malonates was performed using a chiral Lewis acid catalyst prepared from Cu(OTf)(2) and the newly developed spirooxazoline ligand 2 to yield the desired a-chlorinated products with high enantioselectivity (up to 98% ee). Nucleophilic substitution of the resulting chlorides proceeded smoothly to afford a variety of chiral molecules such as alpha-amino, alpha-allcylthio, and alpha-fluoro esters, without loss of enantiopurity. The results of X-ray crystallographic analysis proved that Walden inversion occurs at the chlorinated tertiary carbon center. These results supported the fact that the substitution proceeds via an S(N)2 mechanism.
Umpolung of halide reactivity: efficient (diacetoxyiodo)benzene-mediated electrophilic α-halogenation of 1,3-dicarbonyl compounds
作者:Ramulu Akula、Marc Galligan、Hasim Ibrahim
DOI:10.1039/b915348a
日期:——
An efficient high-yielding (diacetoxyiodo)benzene-mediated α-halogenation of 1,3-dicarbonyl compounds utilising titanium tetrahalides as the halide source has been developed.