Darzens olefin acylation

What is Darzens olefin acylation?

In 1892, Kondakov reported the first instance of a reaction that involves the direct condensation of acyl halides or acyl anhydride and olefins in the presence of Lewis acid. This reaction is commonly referred to as the Kondakov acylation or Kondakov reaction. However, it is also known as the Darzens olefin acylation or the Darzens reaction, named after Darzens’s work in 1910. Suitable Lewis acid catalysts for this condensation include SnCl4, AlCl3, TiCl4, and BF3.

Darzens olefin acylation - general reaction scheme
Darzens olefin acylation

It is important to note that there is a slight difference between the Kondakov acylation and the original Darzens reaction conditions. The latter involves the reaction of acyl halides with alicyclic olefins in the presence of AlCl3. In contrast to the Fridel-Crafts acylation, in which the carbocation from acyl addition can be stabilized, and the recurring of aromaticity leads to a high yield of acylation products, the Darzens olefin acylation often fails due to the formation of various unstable intermediates from electrophilic addition, elimination, and isomerization.

Notably, the acylation of olefins from chloroformates fails almost exclusively, except for one example in which unexpected regiochemistry was obtained. It has been reported that in the presence of a base with low nucleophilicity, both α,β-unsaturated and β,γ-unsaturated ketones may form.

References

  • Kondakov, I. L., Zh. Russ. Fiz-Khim. O-va., 1892, 24, 309
  • Kondakov, I. L., Bull. Soc. Chim. Fr., 1892, 7, 576
  • Kondakoff, J. (1893), Ueber die Synthesen unter dem Einfluss von Zinkchlorid. [On syntheses under the influence of zinc chloride.] J. Prakt. Chem., 48: 467-486. https://doi.org/10.1002/prac.18930480148
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