Heteroarylboronates in Rhodium-Catalyzed 1,4-Addition
to Enones
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Abstract
Rhodium(I)-catalyzed
1,4-addition of aryl and alkenylboronic acids
to α,β-unsaturated carbonyl compounds is well established,
but the transfer of heteroaryl residues in this reaction remains underdeveloped.
We have studied heteroaryl MIDA and pinacol boronates as alternatives
to the labile boronic acid counterparts. Under racemic conditions,
12 adducts with heteroaryl residues, among them unsubstituted 3- and
4-pyridinyl, 2-furanyl, thienyl, and pyrrolyl groups, were obtained
in moderate to excellent yields. The enantioselective version of the
reaction proved highly sensitive to the electronic character of the
heteroaryl substituents, with boronates carrying electron-rich residues
giving modest to high yields but consistently high enantiomeric excesses