Alkoxyallenes in Modern Synthesis: Reactivity, Catalysis, and Complexity Generation

The last decade has witnessed a remarkable transformation in alkoxyallene chemistry. Although historically employed as synthetic equivalents of acrolein or as versatile 3C synthons, alkoxyallenes are now increasingly recognized as highly adaptable platforms for synthetic design. The combination of a polarized cumulene framework, multiple chemically addressable carbon atoms, and diverse activation modes has enabled these substrates to engage in highly selective bond-forming processes across a broad range of reaction manifolds. This review discusses the conceptual and mechanistic advances that have shaped the field, emphasizing how complementary activation strategies can unlock distinct reactivity patterns within the alkoxyallene framework. Recent developments in transition-metal catalysis, radical chemistry, photochemistry, and metallaphotoredox activation have substantially expanded the reactivity profile of these substrates, while the continuing development of lithiated alkoxyallene chemistry has reinforced the exceptional versatility of this class of compounds. Beyond reaction development, the growing use of alkoxyallenes in total synthesis and polymer science underscores their evolution from specialized reactive intermediates into versatile building blocks for both molecular complexity generation and materials-oriented synthesis. Collectively, these studies demonstrate how alkoxyallene chemistry never stopped to reinvent itself, with new activation modes and catalytic strategies steadily expanding the opportunities available to these versatile substrates.