Dargó G, Erdélyi D, Molnár B, Kisszékelyi P, Garádi Z, Kupai J. A novel recyclable organocatalyst for the gram-scale enantioselective synthesis of (
S)-baclofen.
Beilstein J Org Chem 2023;
19:1811-1824. [PMID:
38033451 PMCID:
PMC10682516 DOI:
10.3762/bjoc.19.133]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Accepted: 11/06/2023] [Indexed: 12/02/2023] Open
Abstract
Synthesizing organocatalysts is often a long and cost-intensive process, therefore, the recovery and reuse of the catalysts are particularly important to establish sustainable organocatalytic transformations. In this work, we demonstrate the synthesis, application, and recycling of a new lipophilic cinchona squaramide organocatalyst. The synthesized lipophilic organocatalyst was applied in Michael additions. The catalyst was utilized to promote the Michael addition of cyclohexyl Meldrum's acid to 4-chloro-trans-β-nitrostyrene (quantitative yield, up to 96% ee). Moreover, 1 mol % of the catalyst was feasible to conduct the gram-scale preparation of baclofen precursor (89% yield, 96% ee). Finally, thanks to the lipophilic character of the catalyst, it was easily recycled after the reaction by replacing the non-polar reaction solvent with a polar solvent, acetonitrile, with 91-100% efficiency, and the catalyst was reused in five reaction cycles without the loss of activity and selectivity.
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