Isomerizations of Propargyl 3-Acylpropiolates via Reactive Allenes

Wang, Y.; Hoye, T. R. Org. Lett. 201820, 4425–4429. 

Thermal isomerizations of various propargyl 3-acylpropiolates are described. Many result in the formation of 3-acylbutenolides. These reactions appear to proceed through intermediate 2,3-dehydropyrans (strained cyclic allenes), which then isomerize in a previously unobserved fashion. Competitive processes that provide additional mechanistic insights are also described.