B/N Lewis pairs have been discovered to catalyze rapid epimerization of meso-lactide (LA) or LA diastereomers quantitatively into rac-LA. The obtained rac-LA can be kinetically polymerized into poly(
L
-lactide) and optically resolved
D
-LA, with a high stereoselectivity factor k
L
/k
D
of 53 and an ee value of 91% at 50.6% monomer conversion, by a bifunctional chiral catalyst. The epimerization and enantioselective polymerization can be coupled into a one-pot process for transforming meso-LA directly into poly(
L
-lactide) and
D
-LA.
Organocatalytic asymmetric direct vinylogous Michael addition of α,β-unsaturated γ-butyrolactam to nitroolefins
作者:Abhijnan Ray Choudhury、Santanu Mukherjee
DOI:10.1039/c2ob25832c
日期:——
The first organocatalytic enantioselective directvinylogousMichael reaction of α,β-unsaturatedγ-butyrolactam to nitroolefins is developed using cinchona alkaloids as the catalysts. Both product enantiomers are accessible with moderate to good enantioselectivity.