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The enantioselective construction of quaternary stereogenic centers is considered an
important yet challenging task owing to the involved inherent steric repulsion. Among
different approaches towards this goal, enantioselective desymmetrization of prochiral
molecules emerged as a powerful tool for accessing complex architectures with multiple
stereogenic centers. We have developed an alkylative desymmetrization of prochiral
2,2-disubstituted cyclopentene-1,3-diones, which proceeds via a C(sp2
)−H alkylation.
This work represents the first organocatalytic enantioselective C(sp2
)−H alkylation. We
have now extended this protocol to a more challenging and useful class of substrates.
Once again, the desymmetrized products are obtained with excellent
enantioselectivities.
In addition to this, our works on electrophilic halogen induced heterodifunctionalization
of unactivated olefins and conjugated dienes, namely the iodoetherification of
β,γ-unsaturated oximes and iodoaminocyclization of β,γ-unsaturated hydrazones will
also be discussed. Our methods offer straightforward access to enantioenriched
Δ2
-isoxazolines and Δ2
-pyrazolines containing a quaternary stereogenic center in high
yield and enantioselectivity. |