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.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/4686698
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