First Organocatalyzed Asymmetric Michael Addition of Aldehydes to Vinyl Sulfones
作者:Sarah Mossé、Alexandre Alexakis
DOI:10.1021/ol051488h
日期:2005.9.1
[reaction: see text] The first asymmetric direct Michael addition of aldehydes to vinyl sulfones catalyzed by N-iPr-2,2'-bipyrrolidine is described. 1,4-Adducts are obtained in good yields and enantioselectivities. The determination of absolute configuration allowed us to postulate a Si,Si transition state model, as shown previously for nitroolefins.
1,2-Sulfone rearrangement in organocatalytic reactions
作者:Adrien Quintard、Alexandre Alexakis
DOI:10.1039/c0ob00818d
日期:——
The 1,2-sulfone rearrangement resulting from nucleophilic addition to bis activated vinyl-sulfones has been studied in more detail. Various nucleophiles activated by different types of catalysts (enamine, Brönsted base, thiourea) are able to promote such rearrangement in excellent yields and moderate to excellent enantioselectivities (up to 94% ee). Mechanistic studies have led to a better understanding of the mechanism and allowed its application to other electrophiles such as vinyl-sulfone acrylates.
F rigid cats: The power of conformationallystabilizedcatalysts is demonstrated. By taking appropriate advantage of fluorineinsertion (see scheme), purely conformationalcatalyst design led to a notable improvement in enantioselectivities from around 70 % to 91–98.5 % ee. The other advantage of this approach is the better understanding of the origin of the stereoselectivity in the given catalytic