Conjugate addition to alpha,beta-unsaturated carbonyls derived from Oppolzer’s sultam
Click the structures and reaction arrows in sequence to view the 3D models and animations respectively
The chelation of the carbonyl and sulfonyl oxygen to the magnesium cation restricts the rotation of the acrylamide portion and only S-cis conformation is energetically accessible. Conjugate addition of the organometallic then occurs with high selectivity from underneath to give the R enantiomer only.
W. Oppolzer, Tetrahedron, 1987, 43, 1969–2004.