Transition-Metal Catalyzed, Thermally Driven [2π+2π]-Cycloadditions of Olefins and Alkynes

The [2+2]-cycloaddition of olefins and alkynes stands out as a versatile and atom-economical strategy for synthesizing cyclobutane and cyclobutene building blocks, which are challenging to access through other synthetic methods. While photochemical approaches have traditionally dominated this field, thermally-driven methods employing transition metals offer distinct advantages, including decreased reliance on pre-functionalized substrates and improved scalability. This review explores the underlying principles of metal-catalyzed [2+2]-cycloadditions and highlights recent advances in thermally-driven approaches for the efficient synthesis of cyclobutane and cyclobutene frameworks. Particular attention is given to electronically unbiased substrates, which remain a significant challenge for photochemical approaches.