Asymmetric Benzylic Functionalizations of 3‑Vinyl Benzofurans via Cascade Formal Trienamine–Vinylogous Iminium Ion Activation

An efficient approach to construct chiral 1,1-disubstituted ethane derivatives is presented. This strategy relies on the formation of the key dearomatizative vinylogous iminium ion species through protonation of the formal trienamine intermediates between 2-(3-vinylbenzo­furan-2-yl)­ethan-1-ones and a chiral primary amine. An array of nucleophiles, including 4-hydroxy­coumarins, indoles, etc., have been effectively assembled at the benzylic site, delivering the expected 1,1-disubstituted ethane products in moderate to excellent enantioselectivity.