Advances in umpolung annulations with hypervalent iodine diazos and sulfoxonium ylides

As versatile carbene precursors, diazo compounds and sulfoxonium ylides generate carbenes or metal-carbenes under thermal, photochemical, or transition-metal catalysis, whereas installing a hypervalent iodine fragment at the carbon center converts the intrinsic nucleophilicity of the azomethine carbon or ylide unit and unveils complementary pathways. This review systematically surveys recent advances in umpolung annulations that integrate diazo chemistry/sulfoxonium ylides and hypervalent iodine reagents to achieve electrophilic activation at the diazo/ylide carbon and streamline ring construction. We organize the field by annulation modes, including [2+1], [3+2], [5+1], and other annulations, critically assess the scope across carbo- and heterocycle synthesis, mechanistic foundations, and limitations, and outline future opportunities. Our aim is to provide a coherent framework for this conceptually novel, highly selective, and practical ring-forming strategy using these reagents and to accelerate its wider adoption in synthetic chemistry.