Newman-Kwart Rearrangement

Newman-Kwart Rearrangement

09 May, 2016 / by / in Reactions
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  • General Characteristics

The thermal rearrangement of O-thiocarbamates into S-thiocarbamates is an effective way to synthesize thiophenols from phenols.

The rearrangement usually requires very high thermal conditions (200~300 °C) to proceed, thus microwave irradiation is helpful. Recently, palladium catalysis and photocatalysis have been shown to facilitate the reaction under milder conditions.

  • General References

  • Reaction Mechanism

The O to S rearrangement is driven by the conversion of C=S bond into thermodynamically more stable C=O bond. Since the reaction involves aromatic nucleophilic attack by the sulfur atom, the substrates containing electron-withdrawing groups at ortho or para position react faster.

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The nitrogen must be dialkylated, as protonated O-thiocarbamates are prone to decomposition into isothiocyanates via the following pathway.

Newman_Kwart_2

  • Examples

The reaction can be run at lower temperature (~100 °C) in the presence of a palladium catalyst.[1]

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Ambient-temperature Newman-Kwart rearrangement mediated by organic photoredox catalysis[2]: This recently developed procedure allows the reaction to proceed at room temperature and tolerates a wide range of functional groups.

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  • References

  1. Harvey, J. N.; Jover, J.; Lloyd-Jones, G. C.; Moseley, J. D.; Murray, P.; Renny, J. S. Angew. Chem. Int. Ed., 2009, 48, 7612. DOI: 10.1002/anie.200903908
  2. Perkowski, A. J.; Cruz, C. L.; Nicewicz, D. A. J. Am. Chem. Soc. 2015, 137, 15684. DOI: 10.1021/jacs.5b11800

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