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Reversible carbon protonation in the hydrolysis of heterocyclic enol methyl ethers

✍ Scribed by Brian Capon; Fu-Chiu Kwok

Publisher
Elsevier Science
Year
1987
Tongue
French
Weight
519 KB
Volume
43
Category
Article
ISSN
0040-4020

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✦ Synopsis

The kinetics of the hydronium-ion catalysed hydrolysis of the following heterocyclic methyl enol ethers have been measured: 3-methoxybenzofuran, 3+ethoxybenzothiophene, 3-methoxyindole, 3-methoxy-1-methylindole, 3-methoxyfuran, 3-methoxythiophene. -. and 2-methoxythiophene.

On the basis of the solvent isotope effect kH/kD = 3-.08 and the failure to detect deuterium exchange when the solvent was CDsCD:D20(9:l v/v) it was concluded that the rate limiting step in the hydrolysis of 3-methoxybenzofuran is C-protonation.

The effect of the ring-oxygen atom was measured by comparing the rate of hydrolysis of 3-methoxybenzofuran with that of 3-methoxyinclene which occurs 2100 times faster.

In contrast to the behaviour of 3-methyoxybenzofuran the isotope effects, RH/k

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