Protein Modification by Strain‐Promoted Alkyne–Nitrone Cycloaddition

Quicker and slicker: An efficient metal-free 1,3-dipolar cycloaddition of dibenzocyclooctynes with nitrones proceeded with rate constants of up to 39 M−1 s−1, or up to 300 times faster than similar reactions with azides. This strategy is useful for the site-specific N-terminal modification of peptides and proteins (see scheme).