Gewald reaction

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Gewald reaction
Named after Karl Gewald
Reaction type Ring forming reaction
Identifiers
Organic Chemistry Portal gewald-reaction

The Gewald reaction is an organic reaction involving the condensation of a ketone (or aldehyde when R2 = H) with a α-cyanoester in the presence of elemental sulfur and base to give a poly-substituted 2-amino-thiophene.[1][2]

The Gewald reaction
The Gewald reaction

The reaction is named after the German chemist Karl Gewald (born 1930).[3][4][5]

Reaction mechanism

The reaction mechanism of the Gewald reaction was elucidated 30 years after the reaction was discovered.

tautomerization
will produce the desired product (6).

The mechanism of the Gewald reaction
The mechanism of the Gewald reaction

Microwave irradiation has been shown beneficial to reaction yields and times.[7]

Variations

In one variation of the Gewald reaction a 3-acetyl-2-aminothiophene is synthesized starting from a dithiane (an adduct of sulfur and acetone if R = CH3 or acetaldehyde if R = H) and the sodium salt of cyanoacetone which in itself is very unstable:[8]

1-(2-Amino-4-methyl-3-thienyl)ethanone synthesis
1-(2-Amino-4-methyl-3-thienyl)ethanone synthesis

References

  1. ^ Gewald, K.; Schinke, E.; Böttcher, H. Ber. 1966, 99, 94-100.
  2. ^ Sabnis, R. W. Sulfur Rep. 1994, 16, 1-17. (Review)
  3. ISBN 978-1-4051-3300-5
    .
  4. ISBN 0-471-22854-0
    .
  5. ISBN 978-3-527-30806-4
    .
  6. ^ Sabnis, R. W.; Rangnekar, D. W.; Sonawane, N. D. J. Heterocyclic Chem. 1999, 36, 333.
  7. doi:10.1016/j.tetlet.2007.03.052
    )
  8. ^ Gernot A. Eller, Wolfgang Holzer Molecules 2006, 11, 371-376 Online article.
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