How do carbenes react with acetylenes to form cyclopropenes?

Carbenes react with acetylenes through an addition reaction, which serves as a highly effective method for synthesizing cyclopropenes.

In this process, the carbene—a highly reactive molecule featuring a divalent carbon atom—adds directly across the triple bond of the acetylene. This intermolecular reaction facilitates the formation of a three-membered ring structure. Because carbenes are transient intermediates, this synthetic route is particularly valuable for creating cyclopropenes that might be difficult to obtain through other chemical methods.1