Et2Zn-promoted β-trans-selective hydroboration of ynamide

ABSTRACT The trans-hydroboration of alkyne represents a challenging task in organic synthesis. Reported herein is an Et2Zn promoted β-trans hydroboration of ynamides by using N-heterocyclic carbene (NHC)-ligated borane as boryl source. The reaction leads to a stereoselective construction of enamides bearing a valuable boryl substituent. Both aromatic and aliphatic ynamides were applicable to the reaction. Synthetic transformation of the C-B bond in the product via Suzuki-Miyaura coupling provides a simple and stereospecific route to multi-substituted enamides. Mechanistic studies were conducted and the possible mechanism was discussed