Direct Regio-, Diastereo-, and Enantioselective Vinylogous Michael Addition of Prochiral 3-Alkylideneoxindoles to Nitroolefins

3-Alkylidene-2-oxindoles represent
a simple, yet enabling subfamily of indole alkaloids,
and their ability to react as electron-poor acceptors
has largely been investigated. In contrast, their utility
as pronucleophilic synthons remains elusive. In
this context, the present article describes the successful
execution of the direct, organocatalytic
asymmetric Michael addition of prochiral 3-alkylideneoxindoles
to nitroolefins. A variety of g-substituted
alkylideneoxindoles carrying two stereocenters
at both the g- and d-carbon sites was assembled
with excellent stereoselectivity and without olefin
isomerization or stereochemical ablation.