Expedient Organocatalytic Syntheses of 4-Substituted Pyrazolidines and Isoxazolidines.
MOLECULES (BASEL, SWITZERLAND) 2016;
21:molecules21121655. [PMID:
27916954 PMCID:
PMC6274280 DOI:
10.3390/molecules21121655]
[Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Revised: 11/24/2016] [Accepted: 11/28/2016] [Indexed: 11/17/2022]
Abstract
The efficient organocatalytic synthesis of heterocyclic systems of biological relevance is a subject of growing interest. We have found that the pyrrolidine/benzoic acid-catalyzed reaction of α-substituted propenals such as methacrolein, 2-benzylpropenal and 2-(n-hexyl)propenal with activated hydrazines takes place in very good yields (83%–99.6%) under very mild conditions to afford 4-substituted pyrazolidin-3-ols (as diastereomer mixtures); subsequent oxidation with PCC affords the corresponding-4-substituted-3-pyrazolidinones in essentially quantitative yields. In a similar way, 4-substituted isoxazolidinones are obtained with N-Cbz-hydroxylamine as a reagent. The use of chiral diarylprolinol trimethylsilyl ethers as catalysts allows the synthesis of several of these compounds in optically active form, in some cases with excellent enantioselectivity (up to 96:4 er). A preliminary evaluation of the biological activity shows that some of these compounds exhibit interesting antibacterial and antifungal activities.
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