How does chloroform react with cyclopentadiene in base?
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.