A borylcopper species generated from bis(pinacolato)diboron and its additions to α,β-unsaturated carbonyl compounds and terminal alkynes
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چکیده
The addition of bis(pinacolato)diboron [(Me4C2O2)B-B(O2C2Me4)] to α,β-unsaturated carbonyl compounds giving β-boryl carbonyl compounds and the addition to terminal alkynes yielding either 2-boryl-1-alkenes or 1-boryl-1-alkenes were carried out in DMF at room temperature in the presence of CuCl and AcOK. The transmetalation between diboron and [Cu(Cl)OAc]K generating a borylcopper species was proposed as the key step in the reactions because CuOAc similarly mediated both addition reactions to enones and alkynes in the presence of KCl.
منابع مشابه
Metal free catalytic hydroboration of multiple bonds in methanol using N-heterocyclic carbenes under open atmosphere.
An easy to operate method of catalytic hydroboration of unsaturated compounds has been developed with wide substrate scope. Reactions of various aldimines, ketimines, α,β-unsaturated carbonyl compounds, and alkynes were successfully executed with bis(pinacolato)diboron and N-heterocyclic carbenes in methanol without requiring a transition metal or inert atmosphere.
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A method for the synthesis of 1,1-diborylalkenes through a Brønsted base catalyzed reaction between terminal alkynes and bis(pinacolato)diboron has been developed. The procedure allows direct synthesis of functionalized 1,1-diborylalkenes from various terminal alkynes including propiolates, propiolamides, and 2-ethynylazoles.
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Enantioselective conjugate addition of bis(pinacolato)diboron to α,β-unsaturated imines proceeds smoothly in water in the presence of a chiral copper(II) complex consisting of Cu(OAc)2 and chiral 2,2'-bipyridine. The corresponding β-boryl imines, which were oxidized to β-hydroxy imines, further leading to γ-amino alcohols, were obtained in high yields and high enantioselectivities.
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The α,β-unsaturated sulfones are suitable activated olefins in catalytic asymmetric conjugate β-boration. These substrates undergo smooth conjugate addition of bis(pinacolato)diboron [B(2)(pin)(2)] catalyzed by nonracemic Cu(I)-diphosphine complexes to provide, upon subsequent oxidation, β-hydroxy sulfones in good yields and high enantiocontrol.
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