Copper- Catalyzed Asymmetric Synthesis by Alexakis, Krause and Woodward : Content: 12.2 Conjugate Addition: Asymmetric copper-catalyzed conjugate addition reaction is a versatile and a very useful organic transformation. Progress in this area has been covered inseveral reviews [14–23]. The mechanism for nonstabilized nucleophiles (e.g.,RMgX, ZnR2, AlR3) is thought to share much of the characteristics from the stoichiometric versions involving lithium organocuprates . The general
catalytic cycle involves a transmetallation of the nucleophile to CuI with the
stoichiometric metal staying associated and functioning as a Lewis acid in the
following steps: formation of a π-complex with the enone and either an
oxidative addition (to a σ-complex) followed by reductive elimination or a
carbocupration (1,2-migratory insertion) with subsequent rearrangement to
reform the copper catalyst (Scheme 12.2). Cu(I) is thought to be the active
catalyst although Cu(II)-salts are the most commonly used precatalysts
because they are less hygroscopic and air sensitive. NMR and EPR (electron
paramagnetic resonance) studies support the theory of in situ reduction of
Cu(II) to Cu(I) .
Download to Read More….
Thanks For Visiting Our Website www.freepdfbook.com To Support Us, Keep Share On Social Media.