Dynamic Control of Chiral Space Through Local Symmetry Breaking in a Rotaxane Organocatalyst
作者:Marcel Dommaschk、Javier Echavarren、David A. Leigh、Vanesa Marcos、Thomas A. Singleton
DOI:10.1002/anie.201908330
日期:2019.10.14
We report on a switchable rotaxane molecular shuttle that features a pseudo-meso 2,5-disubstituted pyrrolidine catalytic unit on the axle whose localsymmetry is broken according to the position of a threaded benzylic amide macrocycle. The macrocycle can be selectively switched (with light in one direction; with catalytic acid in the other) with high fidelity between binding sites located to either
2-position, gave a synergistic effect leading to two powerful complementary organocatalysts. They show excellent enantiocontrol in the -functionalization of a wide range of linear/branched aldehydes and ketones, including Michael additions to ethenediyl disulfones or nitrostyrene and -amination. We obtained ees up to 98.5 % with low catalyst loadings (down to 1 mol-%). As a proof of efficiency, TOFs of up to
Chiral framework: Chiral amines with pyrrolidine frameworks catalyze the enantioselective conjugate addition of a wide range of aldehydes to various vinyl sulfones and vinyl phosphonates in high yields and with enantioselectivities up to >99 % ee (see scheme). The high versatility of the Michael adducts is exemplified by various functionalizations with conservation of the optical purity.
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