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.