Catalytic, Enantioselective C2-Functionalization of 3-Aminobenzofurans Using N-Heterocyclic Carbenes.

N-Heterocyclic carbene catalyzed enantioselective functionalization of 3-aminobenzofurans at the C2-position was realized using 2-bromoenals as the coupling partner. The reaction proceeds via generation of chiral α,β-unsaturated acylazoliums and follows an aza-Claisen rearrangement. The initially formed dihydropyridinone undergoes ring-opening catalyzed by Mg to afford the δ-amino acid derivatives. The reaction worked with 3-aminobenzothiophenes as well, and the C2-alkylated products were formed in moderate to high yields and selectivity.