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    2-Diazo-1-(4-hydroxyphenyl)ethanone: A Versatile Photochemical and Synthetic Reagent

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    Issue Date
    2014-02
    Author
    Senadheera, Sanjeewa N.
    Evans, Anthony S.
    Toscano, John P.
    Givens, Richard S.
    Publisher
    Royal Society of Chemistry
    Type
    Article
    Article Version
    Scholarly/refereed, author accepted manuscript
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    Abstract
    α-Diazo arylketones are well-known substrates for Wolff rearrangement to phenylacetic acids through a ketene intermediate by either thermal or photochemical activation. Likewise, α-substituted p-hydroxyphenacyl (pHP) esters are substrates for photo-Favorskii rerrangements to phenylacetic acids by a different pathway that purportedly involves a cyclopropanone intermediate. In this paper, we show that the photolysis of a series of α-diazo-p-hydroxyacetophenones and p-hydroxyphenacyl (pHP) α-esters both generate the identical rearranged phenylacetates as major products. Since α-diazo-p-hydroxyacetophenone (1a, pHP N2) contains all the necessary functionalities for either Wolff or Favorskii rearrangement, we were prompted to probe this intriguing mechanistic dichotomy under conditions favorable to the photo-Favorskii reangement, i.e., photolysis in hydroxylic media. An investigation of the mechanism for conversion of 1a to p-hydroxyphenyl acetic acid (4a) using time-resolved infrared (TRIR) spectroscopy clearly demonstrates the formation of a ketene intermediate that is subsequently trapped by solvent or nucleophiles. The photoreaction of 1a is quenched by oxygen and sensitized by triplet sensitizers and the quantum yields for 1a–c range from 0.19 to a robust 0.25. The lifetime of the triplet, determined by Stern-Volmer quenching, is 15 ns with a rate for appearance of 4a of k = 7,1 × 106 s−1 in aq. acetonitrile (1:1 v:v). These studies establish that the primary rearrangement pathway for 1a involves ketene formation in accordance with the photo-Wolff rearrangement. Furthermore we have also demonstrated the synthetic utility of 1a as an esterification and etherification reagent with a variety of substituted α-diazo-p-hydroxyacetophenones, using them as synthons for efficiently coupling it to acids and phenols to produce pHP protect substrates.
    URI
    http://hdl.handle.net/1808/24673
    DOI
    https://doi.org/10.1039/c3pp50305d
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    • Chemistry Scholarly Works [626]
    Citation
    Senadheera, S. N., Evans, A. S., Toscano, J. P., & Givens, R. S. (2014). 2-Diazo-1-(4-hydroxyphenyl)ethanone: A Versatile Photochemical and Synthetic Reagent. Photochemical & Photobiological Sciences : Official Journal of the European Photochemistry Association and the European Society for Photobiology, 13(2), 324–341. http://doi.org/10.1039/c3pp50305d

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    Contact KU ScholarWorks
    785-864-8983
    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    785-864-8983

    KU Libraries
    1425 Jayhawk Blvd
    Lawrence, KS 66045
    Image Credits
     

     

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