Organocatalyzed Asymmetric Dearomative Aza-Michael/Michael Addition Cascade of 2‑Nitrobenzofurans and 2‑Nitrobenzothiophenes with 2‑Aminochalcones

An organocatalyzed dearomative aza-Michael/Michael
addition cascade
of 2-nitrobenzofurans and 2-nitrobenzothiophenes with 2-aminochalcones
has been developed, opening a new channel to access a series of optically
active tetrahydrobenzofuro­[3,2-b]­quinolines and tetrahydrobenzo­[4,5]­thieno­[3,2-b]­quinolines bearing three contiguous stereocenters with
excellent diastereo- and enantioselectivities (all cases >20:1
dr,
up to 99% ee). This study features the first asymmetric dearomative
cascade reaction of 2-nitrobenzofurans and 2-nitrobenzothiophenes
beginning with aza-Michael addition. The potential applications of
the methodology were demonstrated by the preparative-scale experiment
and the versatile transformations of the products.