Schönberg rearrangement

What is Schönberg rearrangement?

The rearrangement of the methyl xanthate of diacetonehexose was initially reported by Freudenberg in 1927. Subsequently, Schönberg studied the thermal transformation of thioncarbonates (O-aryl) into thiolcarbonates (S-aryl) in 1930, making it commonly known as the Schönberg rearrangement or Schönberg reaction.

Schönberg rearrangement - general reaction scheme - Schönberg reaction
Schönberg rearrangement

The reaction is favored when Y is an ortho– or para-electron-withdrawing group.

Schönberg rearrangement has been extensively studied for aryl thioncarbonates or xanthates that lack a β-hydrogen atom, while thioncarbonates or xanthates with a β-hydrogen atom can also undergo competing pyrolysis (e.g., Chugaev reaction) to form olefins.

The Schönberg rearrangement is thought to be driven by the higher nucleophilic character of the sulfur atom and the electron-donating capability of the aryl or alkyl group. Therefore, electron-withdrawing groups at the ortho– and para-positions of the O-aryl moiety facilitate the rearrangement.

Schönberg rearrangement is important for converting phenols to thiophenols, particularly for some substituted thiophenols that are challenging to prepare using other methods.

References

  • Freudenberg, K. and Wolf, A., Ber., 1927, 60, 232
  • Schönberg, A. and Vargha, L., Ber., 1930, 63, 178
  • Schönberg, A.; Vargha, L. and Paul, W., Ann., 1930, 483, 107
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