Hydrogen-Bond-Donor-Directed
Switching of Enantioselectivity
in the Vinylogous Aldol–Cyclization Cascade Reaction of Prostereogenic
3‑Alkylidene Oxindoles with Isatins and o‑Quinones
posted on 2022-01-27, 18:34authored byYun-Jie Tsou, Nadaraj Sathishkumar, I-Ting Chen, Ting-An Lee, Hsin-Tsung Chen, Jeng-Liang Han
In
this study, we reported a hydrogen-bond-donor-directed enantiodivergent
vinylogous aldol–cyclization cascade reaction of 3-alkylidene
oxindoles with isatins and o-quinones. Both enantiomers
can be prepared by thiourea or squaramide cinchona alkaloid bifunctional
organocatalysts with the same quinine scaffold. Kinetic study data
provided the possible reaction mechanism for the vinylogous aldol–cyclization
cascade reaction. The DFT calculation data showed the geometry of
the generated dienolates from pronucleophiles dominated the observed
switch of enantioselectivity.