Figure . Selected fused seven-membered ring systems containing natural products. method was developed. To the best of our knowledge, the De Mayo reaction was pioneered by De Mayo and subsequently enriched by De Mayo, Weedon, Bach, and other groups. Until now, the De Mayo reaction has still been a powerful and versatile tool for constructing polycyclic compounds using β-ketoenols and olefins induced by ultraviolet light. Based on this strategy, many complex natural products, and biologically active small molecules have been created. With the rapid development of photoredox catalysts, radical chemistry has emerged as a vital and powerful platform to achieve multiple and efficient transformations under mild conditions. One prominent example is a more recent study by Glorius and co-workers that showcased a visible-light photocatalyzed two-carbon homologation of carbonyl compounds based on a novel iridium catalyst system to access medium-sized carbocycles (Scheme 1c). Although this protocol presented the important aspect of generality, the unsatisfying regioselectivity has limited its synthetic applications in total synthesis. Scheme 1. Synthetic Strategies toward the fused seven-membered ring systems.