Organocatalytic Coupling of Bromo-Lactide with Cyclic Ethers and Carbonates to Chiral Bromo-Diesters: NHC or Anion Catalysis?
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AbstractIn 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 experimental and computational studies led to a coupling mechanism that proceeds through an anion (bromide)-mediated catalytic cycle, rather than an apparent NHC-catalyzed cycle.
CitationZhu J-B, Tang X, Falivene L, Caporaso L, Cavallo L, et al. (2017) Organocatalytic Coupling of Bromo-Lactide with Cyclic Ethers and Carbonates to Chiral Bromo-Diesters: NHC or Anion Catalysis? ACS Catalysis 7: 3929–3933. Available: http://dx.doi.org/10.1021/acscatal.7b00794.
SponsorsThis work was supported by the US National Science Foundation (NSF-1507702) and the W.M. Keck Foundation for the study carried out at Colorado State University, and by the funding from King Abdullah University of Science and Technology (KAUST) for the study performed at KAUST. The computing resources and the related technical support used by the University of Salerno have been provided by CRESCO/ENEAGRID High Performance Computing infrastructure and its staff.
PublisherAmerican Chemical Society (ACS)