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Is my reaction mechanism feasible?

  • 1
    $\begingroup$ Isn't it abnormal Riemann tiemann reaction?? $\endgroup$
    – Carrick
    Apr 30, 2019 at 14:12

1 Answer 1


The worry I had is that the normal way to make dichlorocarbene from chloroform is to treat it with a strong base, this will convert the cyclopentadiene into the cyclopentadienyl anion. This anion is an aromatic species which is unlikely to be able to react with the carbene.

But in one paper (Grignon-Dubois, M.; Dunogues, J.; Ahra, M. - Recueil des Travaux Chimiques des Pays-Bas, 1988, vol. 107, # 3, p. 216 - 225) it has been reported that chloroform, base and cyclopentadiene will react together to form the first intermidate.

I think that the reaction step showing the formation of the cyclopropane ring is perfectly reasonable. We need to consider how we would form the carbene. I know that it is possible to form carbene by a photochemical reaction on ketene which forms the carbene and carbon monoxide. I know from personal experience that chloroketene reacts in a [2+2] reaction with cyclopentadiene to form a cyclobutanone. So that route might not be a good idea.

  • 2
    $\begingroup$ The abstract of this paper pubs.rsc.org/en/content/articlelanding/1971/c2/… records that under very similar conditions the product of cyclopentadiene and dichlorocarbene is 6-Cl-fulvene. It is behind a paywall so I cannot read the full paper. $\endgroup$
    – Waylander
    Jun 3, 2018 at 9:12
  • $\begingroup$ @NuclearChemist In your first paragraph, last line you state that, "* This anion is an aromatic species which is unlikely to be able to react with the carbene.*" Why?, In reimer teimann reaction it is completely fine for the aromaticity to break momentarily? $\endgroup$
    – Rishi
    Jul 13, 2021 at 10:31

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