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Enantioselective Michael addition of 1,3-dicarbonyl compounds to a nitroalkene catalyzed by chiral squaramides – a key step in the synthesis of pregabalin†
Rastislav Baran,Eva Veverková,Andrea Škvorcová,Radovan Šebesta
Organic & Biomolecular Chemistry Pub Date : 09/24/2013 00:00:00 , DOI:10.1039/C3OB41709C
Abstract

Asymmetric organocatalytic 1,4-additions provide access to a large number of biologically relevant compounds. Chiral squaramides efficiently catalyse enantioselective Michael addition of 1,3-dicarbonyl compounds to aliphatic nitroalkenes. The resulting γ-nitro carboxylic derivatives were obtained in high yields and in high enantiomeric purities. Quantum chemical calculations helped us to devise a transition state model, which explains the observed stereochemical course of the addition. The best results were obtained with Meldrum's acid as a donor, with which enantiomeric purity of the Michael adduct was 97 : 3 e.r. Using this methodology pregabalin was synthesized in three steps in overall 52% yield.

Graphical abstract: Enantioselective Michael addition of 1,3-dicarbonyl compounds to a nitroalkene catalyzed by chiral squaramides – a key step in the synthesis of pregabalin
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