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  • 1.
    Andersson, Hans
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Reaction Between Grignard reagents and Heterocyclic N-oxides: Synthesis of Substituted Pyridines, Piperidines and Piperazines2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis describes the development of new synthetic methodologies for preparation of bioactive interesting compounds, e.g. substituted pyridines, piperidines or piparazines. Thesecompounds are synthesized from commercially available, cheap and easily prepared reagents, videlicet the reaction between Grignard reagents and heterocyclic N-oxides.

     The first part of this thesis deals with an improvement for synthesis of dienal-oximes and substituted pyridines. This was accomplished by a rapid addition of Grignard reagents to pyridine N-oxides at rt. yielding a diverse set of substituted dienal-oximes. During these studies, it was observed that the obtained dienal-oxmies are prone to ring-close upon heating. By taking advantage of this, a practical synthesis of substituted pyridines was developed.

    In the second part, an ortho-metalation of pyridine N-oxides using Grignard reagents is discussed. The method can be used for incorporation of a range of different electrophiles, including aldehydes, ketones and halogens. Furthermore, the importance for incorporation of halogens are exemplified through a Suzuki–Miyaura coupling reaction of 2-iodo pyridine N-oxides and different boronic acids. Later it was discovered that if the reaction temperature is kept below -20 °C, the undesired ringopening can be avoided. Thus, the synthesis of 2,3-dihydropyridine N-oxide, by reacting Grignard reagents with pyridine N-oxides at -40 °C followed by sequential addition of aldehyde or ketone, was accomplished. The reaction provides complete regio- and stereoselectivity yielding trans-2,3-dihydropyridine N-oxides in good yields. These intermediate products could then be used for synthesis of either substituted piperidines, by reduction, or reacted in a Diels–Alder cycloaddtion to give the aza-bicyclo compound.

    In the last part of this thesis, the discovered reactivity for pyridine N-oxides, is applied on pyrazine N-oxides in effort to synthesize substituted piperazines. These substances are obtained by the reaction of Grignard reagents and pyrazine N-oxides at -78 °C followed by reduction and protection, using a one-pot procedure. The product, a protected piperazine, that easily can be orthogonally deprotected, allowing synthetic modifications at either nitrogens in a fast and step efficient manner. Finally, an enantioselective procedure using a combination of PhMgCl and (-)-sparteine is discussed, giving opportunity for a stereoselective synthesis of substituted piperazines.

  • 2.
    Andersson, Hans
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Almqvist, Fredrik
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Olsson, Roger
    Synthesis of 2-Substituted Pyridines via a Regiospecific Alkylation, Alkynylation, and Arylation of Pyridine N-Oxides2007Ingår i: Organic Letters, Vol. 9, nr 7, s. 1335-7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sequential addition of Grignard reagents to pyridine N-oxides in THF at room temperature followed by treatment with acetic anhydride at 120 C afforded 2-substituted pyridines in good to high yields. Furthermore, by exchanging acetic anhydride for DMF in the second step, 2-substituted pyridine N-oxides were obtained, as intermediates suitable for addition of a second Grignard reagent for the synthesis of 2,6-disubstituted pyridines.

  • 3.
    Andersson, Hans
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Gustafsson, Magnus
    Olsson, Roger
    Almqvist, Fredrik
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Selective synthesis of 2-substituted pyridine N-oxides via directed ortho-metallation using Grignard reagents2008Ingår i: Tetrahedron Letters, Vol. 49, nr 48, s. 6901-3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Addition of i-PrMgCl to pyridine N-oxides in THF at −78 °C generates selectively an ortho-metallated species, which can be trapped with various electrophiles to generate 2-substituted pyridine N-oxides. Furthermore, by applying a double metal-catalyzed cross-coupling, direct arylation of the pyridine N-oxides is achieved.

  • 4.
    Andersson, Hans
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Wang, Xiaoyang
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Björklund, Mikael
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Olsson, Roger
    Almqvist, Fredrik
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Reaction of pyridine N-oxides with Grignard reagents: a stereodefined synthesis of substituted dienal oximes2007Ingår i: Tetrahedron Letters, Vol. 48, s. 6941-4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rapid addition of Grignard reagents to pyridine N-oxides under mild conditions gave stereodefined dienal oximes in good to excellent yields. This reaction provides an efficient access to substituted olefins with defined stereochemistry that are potentially of interest as bioactives themselves or as versatile synthetic intermediates.

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