LAUSR

For the first time, a simple methodology for the chemical synthesis and use of highly reactive 4‐methylenoxazol‐5(4H)‐ones from serine is presented. These dehydroalanine derivatives, which resemble the natural 4‐methylidenimidazole‐5‐one (MIO) cofactor present in lyases and aminomutases, undergo rapid reaction with carbon nucleophiles such as silyl enol ethers, as well as cycloaddition reactions with diazo compounds and reactive dienes, under very mild conditions and without any need for metal catalysts or ring‐strain activation, offering potential for bioconjugation.