An Expeditious Route to Chiral δ-Aminoesters and Piperidones

An Expeditious Route to Chiral δ-Aminoesters and Piperidones

Author: Claire D'Andola

Conjugate addition reactions play a crucial role in organic synthesis. Research on these transformations has been boosted by the wide diversity of compounds that can serve as nucleophiles and electrophiles in the reaction to generate a varied array of products. In contrast to carbonyl substrates and nitroalkenes, asymmetric conjugate addition to α,β-unsaturated imines has been scarcely explored, probably due to the lower electrophilicity of these substrates. Only a small number of examples regarding the enantioselective 1,4-nucleophilic addition of carbon nucleophiles to unsaturated imines have been reported.

Gonzalo Blay, José R. Pedro and co-workers, Universitat de València, Spain, report the first example of the asymmetric conjugate addition of malonate esters to α,β-unsaturated N-sulfonyl imines. The reactions are catalyzed by PyBOX/La(OTf)3 complexes in the presence of 4 Å molecular sieves. They give the corresponding E enamines bearing a stereogenic center at the allylic position with good yields and enantiomeric ratios up to 97:3 (see scheme).

These compounds are effective synthons for the preparation of optically active δ-aminoesters bearing two stereogenic centers at the β and δ-positions, and for the preparation of optically active piperidones.

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