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ABSTRACT: We report here reactions between a free carbene center and a suitably appended -bond (C=X) that give rise to reactive intermediates that, in turn, undergo various types of additional transformations (cycloadditions, rearrangements, and ring-openings). Participation of the following C=X functional groups is demonstrated: alkene, arene, heteroarene, aldehyde, ester, ketone, amide, and carbamate. The overall transformations are thermally driven and often produce no byproducts. Each is initiated by the generation of a carbene that is fueled by the potential energy provided by two complementary alkyne co-reactants. 

Pyrrole and 2-pyrrolone derivatives are valuable heterocyclic compounds and while classical condensation methods for their synthesis have a long history, many of the recent developments for their preparation involve the use of transition metal catalysis. Here we report a complementary, metal-free strategy for constructing structurally diverse derivatives of these heterocycles. The key feature of the approach is the in situ creation of a reactive intermediate by an initial facile event that simultaneously generates a pyrrole ring bearing a free carbene. This is straightforwardly accessed via a spontaneous, net [3 + 2] cyclization reaction of a linear alkynyl O-silylimidate or alkynyl aldimine with an electrophilic alkyne. The carbene then undergoes either 1,4-silyl migration (to produce 2-pyrrolone derivatives) or C–H insertion, cycloaddition, cyclopropanation or macrocyclization reactions (leading to pyrrole derivatives).