“…In carbene chemistry, transition-metal catalysts with periodic table group 8–11 elements are commonly employed as a catalytic core to generate metal–carbene species from corresponding diazo compounds or their related precursors (Figure a). Metal-carbene reactions using unique catalyst platforms with Rh, , Cu, , Pd, , Ir, Ru, , Co, Au , etc., to achieve carbon homologation have been tremendously successful . To reduce the environmental load, the development of transition-metal free reactions using various conditions and reagents, such as blue light, Brønsted acid, − organic silanes, and organoboranes, has gained momentum.…”