Lewis Acid Promoted Trapping of Chiral Aza-enolates

We present a study on sequential conjugate addition of
Grignard reagents to alkenyl-heteroarenes followed by trapping of the
resulting enolates, yielding moderate to good diastereoselectivities.
Contrary to conventional wisdom, one-pot conjugate addition/trapping
using two reactive Michael acceptors in combination with Grignard reagents
can proceed via conjugate addition to the least reactive Michael
acceptor. This unusual chemoselectivity is triggered by the presence of
a Lewis acid, reverting the usual reactivity order of Michael acceptors