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    α-Keto amides as precursors to heterocycles—generation and cycloaddition reactions of piperazin-5-one nitrones


    Heaney, Frances and Fenlon, Julie and McArdle, Patrick and Cunningham, Desmond (2003) α-Keto amides as precursors to heterocycles—generation and cycloaddition reactions of piperazin-5-one nitrones. Organic and Biomolecular Chemistry, 1 (7). pp. 1122-1132. ISSN 1477-0520

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    Abstract

    α-Keto amides 10a,b, formed from reaction of pyruvic or benzoylformic acid with allyl amine are found to present as single rotameric forms whilst their tertiary amido analogues 10c,d present as two rotamers in solution at rt. The hydroxyimino derivatives 8 share the conformational characteristics of their parents. The geometrical make-up of the new α-amidooximes is seen to depend on the structure of the starting acid and on the degree of substitution of the amido group. The oxime 8a derived from pyruvic acid and allyl amine is formed solely as the (E)-isomer whilst its tertiary amido analogue 8c is formed as both (E)- and (Z)-isomers. Oximes derived from benzoylformic acid have the opposite selectivity with both geometrical isomers forming from the secondary amide 8b and only the (Z)-isomer from the tertiary amide 8d. With the exception of 8b all oximes were configurationally stable with (Z)-isomers reacting to form isoxazolopyrrolidinones 11—compounds with a relatively rare bicyclic nucleus and (E)-isomers cyclising to piperazin-5-one nitrones 1—ketopiperazine N-oxides have to date only appeared once in the literature. New nitrones were trapped with phenyl vinyl sulfone, dimethyl acetylenedicarboxylate and methyl propiolate yielding isoxazolidine and isoxazoline fused piperazinones 13,15,21 and 22. Cycloadducts from dimethyl acetylenedicarboxylate and 8a,b are thermally labile and their rearrangement provides a novel route to pyrrolopiperazinones 16. The structure of a representative isoxazolopyrrolidinone, 11c, and a 2,3-dihydroisoxazoline fused piperazinone, 21b, are unambiguously solved following x-ray structural analysis.

    Item Type: Article
    Keywords: alpha-Keto amides; heterocycles; generation; cycloaddition reactions; piperazin-5-one nitrones;
    Academic Unit: Faculty of Science and Engineering > Chemistry
    Item ID: 7961
    Identification Number: https://doi.org/10.1039/B210943N
    Depositing User: Dr. Frances Heaney
    Date Deposited: 24 Feb 2017 16:34
    Journal or Publication Title: Organic and Biomolecular Chemistry
    Publisher: Royal Society of Chemistry
    Refereed: Yes
    Funders: Enterprise Ireland (EI)
    URI:

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