1448901-30-1Relevant articles and documents
Reductive α-borylation of α,β-unsaturated esters using NHC-BH3 activated by I2 as a metal-free route to α-boryl esters
Radcliffe, James E.,Fasano, Valerio,Adams, Ralph W.,You, Peiran,Ingleson, Michael J.
, p. 1434 - 1441 (2019)
Useful α-boryl esters can be synthesized in one step from α,β-unsaturated esters using just a simple to access NHC-BH3 (NHC = N-heterocyclic carbene) and catalytic I2. The scope of this reductive α-borylation methodology is excellent and includes a range of alkyl, aryl substituted and cyclic and acyclic α,β-unsaturated esters. Mechanistic studies involving reductive borylation of a cyclic α,β-unsaturated ester with NHC-BD3/I2 indicated that concerted hydroboration of the alkene moiety in the α,β-unsaturated ester proceeds instead of a stepwise process involving initial 1,4-hydroboration; this is in contrast to the recently reported reductive α-silylation. The BH2(NHC) unit can be transformed into electrophilic BX2(NHC) moieties (X = halide) and the ester moiety can be reduced to the alcohol with the borane unit remaining intact to form β-boryl alcohols. The use of a chiral auxiliary, 8-phenylmenthyl ester, also enables effective stereo-control of the newly formed C-B bond. Combined two step ester reduction/borane oxidation forms diols, including excellent e.e. (97%) for the formation of S-3-phenylpropane-1,2-diol. This work represents a simple transition metal free route to form bench stable α-boryl esters from inexpensive starting materials.
N-Heterocyclic Carbene Boryl Iodides Catalyze Insertion Reactions of N-Heterocyclic Carbene Boranes and Diazoesters
Allen, Thomas H.,Kawamoto, Takuji,Gardner, Sean,Geib, Steven J.,Curran, Dennis P.
supporting information, p. 3680 - 3683 (2017/07/15)
Boron-hydrogen bond insertion reactions of N-heterocyclic carbene (NHC) boranes and diazoesters can be catalyzed by NHC-boryl iodides and produce stable α-NHC-boryl esters. The conditions of the reaction resemble the previous rhodium-catalyzed transformations (only the catalyst is different); however, the mechanisms of the two reactions are probably very different. The new boryl iodide catalyzed method is adept at producing α-substituted-α-NHC-boryl esters, and this has led to a family of NHC-boryl esters with amino acid and amino-acid-like side chains.
