Fischer indole synthesis on unsymmetrical ketones. The effect of the acid catalyst
- 1 January 1969
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society B: Physical Organic
- p. 446-449
- https://doi.org/10.1039/j29690000446
Abstract
The products of the Fischer indole synthesis on the unsymmetrical ketones MeCO·CHR1R2(R1= H or Me; R2= Me or Ar) have been found to vary with the acid catalyst, and particularly with the concentration of phosphoric oxide dissolved in orthophosphoric acid. Ethyl, phenethyl, and p-nitrophenethyl methyl ketones give mixtures of substituted 1H-indoles [(II) and (III)] while isopropyl methyl ketone gives a mixture of substituted 1H-(III) and 3H-indoles (IV). In all of the reactions the proportion of the 2-substituted indole (III) increases from 0% in acid mixtures such as 90%(w/w) orthophosphoric acid or 30%(w/w) sulphuric acid, to become the major component in the mixtures near 83%(w/w) phosphoric oxide in water or 70%(w/w) sulphuric acid. A mechanistic interpretation of these results is presented.Keywords
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