Hemetsberger indole synthesis

Hemetsberger indole synthesis
Named after Helfried Hemetsberger
Reaction type Ring forming reaction

The Hemetsberger indole synthesis (also called the Hemetsberger–Knittel synthesis) is a chemical reaction that thermally decomposes a 3-aryl-2-azido-propenoic ester into an indole-2-carboxylic ester.[1][2]

The Hemetsberger indole synthesis
The Hemetsberger indole synthesis

Yields are typically above 70%. However, this is not a popular reaction, due to the lack of stability and difficulty in synthesizing the starting material.

Reaction mechanism

The mechanism is unknown. However, azirine[3] intermediates have been isolated. The mechanism is postulated to proceed via a nitrene intermediate.[4]

References
  1. Hemetsberger, H.; Knittel, D. (1972). "Synthese und Thermolyse von α-Azidoacrylestern". Monatshefte für Chemie. 103: 194–204. doi:10.1007/BF00912944. S2CID 91741917.
  2. Gribble, G. W. (2000). "Recent developments in indole ring synthesis-methodology and applications". J. Chem. Soc., Perkin Trans. (7): 1045–1075. doi:10.1039/a909834h.
  3. Gilchrist, T. L. (2001). "Activated 2H-Azirines as Dienophiles and Electrophiles" (PDF). Aldrichimica Acta. 34 (2): 51. Archived from the original (PDF) on 15 May 2013.
  4. Knittel, D. (1985). "Verbesserte Synthese von α-Azidozimtsäure-estern und 2H-Azirinen". Synthesis. 1985 (2): 186–188. doi:10.1055/s-1985-31149.
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