In the presence of a N-heterocyclic carbene (NHC) in THF, Br-substituted L-lactide (Br-LA) unexpectedly undergoes exclusive coupling with THF to form a chiral ω-bromo-α-keto-diester. This coupling reaction is completely selective (in a precise 1:1 fashion), readily scalable (>20 g scale), and extremely efficient (with only 50 ppm of NHC loading). Other cyclic ethers and carbonates can also undergo similar coupling with Br-LA, thus offering a class of Br-functionalized chiral diesters with various functions and chain lengths. Combined exptl. and computational studies led to a coupling mechanism that proceeds through an anion (bromide)-mediated catalytic cycle, rather than an apparent NHC-catalyzed cycle.
Organocatalytic Coupling of Bromo-Lactide with Cyclic Ethers and Carbonates to Chiral Bromo-Diesters: NHC or Anion Catalysis?
Falivene, Laura;CAPORASO, Lucia;CAVALLO, LUIGI;
2017-01-01
Abstract
In the presence of a N-heterocyclic carbene (NHC) in THF, Br-substituted L-lactide (Br-LA) unexpectedly undergoes exclusive coupling with THF to form a chiral ω-bromo-α-keto-diester. This coupling reaction is completely selective (in a precise 1:1 fashion), readily scalable (>20 g scale), and extremely efficient (with only 50 ppm of NHC loading). Other cyclic ethers and carbonates can also undergo similar coupling with Br-LA, thus offering a class of Br-functionalized chiral diesters with various functions and chain lengths. Combined exptl. and computational studies led to a coupling mechanism that proceeds through an anion (bromide)-mediated catalytic cycle, rather than an apparent NHC-catalyzed cycle.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
