Ligand-Enabled, Copper-Catalyzed Regio- and Stereoselective Synthesis of Trialkylsubstituted Alkenylboronates from Unactivated Internal Alkynes.
We report the first copper-catalyzed regio- and stereoselective borylalkylation of dialkylsubstituted internal alkynes with bis(pinacolato)diboron and alkyl halides. A catalytically generated borylcopper species containing a novel π-accepting N-heterocyclic carbene ligand chemoselectively reacted with unactivated internal alkynes over alkyl halides. The intermediate alkenylcopper species subsequently reacted with alkyl halides, affording the desired products. The copper catalyst differentiated steric demands between the two aliphatic substituents on the C≡C triple bond of the alkyne substrates to exhibit high regioselectivity from a wide range of alkyne/alkyl halide combinations. This method is useful for the straightforward synthesis of trialkylsubstituted alkenylboronates, i.e., versatile precursors for tetrasubstituted alkenes containing three or four different alkylsubstituents, which are difficult to synthesize by other methods.
Graduate School of Pharmaceutical Sciences, The University of Tokyo , Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Taisuke
T
Itoh
Graduate School of Pharmaceutical Sciences, The University of Tokyo , Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Yohei
Y
Shimizu
Graduate School of Pharmaceutical Sciences, The University of Tokyo , Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.|Kanai Life Science Catalysis Project, ERATO, Japan Science Technology Agency , Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Motomu
M
Kanai