SRN1

SRN1 refers to a radical-chain mechanism for nucleophilic substitution of halogenated arenes and related substrates under reducing conditions. The process proceeds by single-electron transfer from a nucleophile or donor to the substrate, generating a radical anion that fragments to an aryl (or vinyl) radical and a halide ion. The resulting radical then participates in chain propagation by transferring an electron to another substrate molecule or by reacting with the nucleophile to form the substitution product, regenerating reactive species that continue the cycle.

Substrates compatible with SRN1 are typically aryl or vinyl halides that can be reduced to a stabilized radical anion, often those bearing electron-withdrawing groups. The reaction can tolerate a variety of nucleophiles, including amines, alkoxides, thiolates, and organometallics, enabling C–N, C–O, C–S, and some C–C bond formations. The mechanism is radical in nature, which can lead to lower stereocontrol and side reactions such as dimerization or hydrogen abstraction, depending on conditions.

Initiation is usually achieved via photochemical activation or chemical reducing conditions, such as dissolving-metal reductions or strong electron-donor reagents. Propagation steps can be sensitive to solvent, temperature, and the presence of radical scavengers. Because it relies on radical intermediates, SRN1 provides a complementary route to classical SNAr for substrates that are difficult to activate by nucleophilic substitution.

In summary, SRN1 is a radical-chain substitution mechanism enabling nucleophilic displacement of halides on activated substrates under reducing conditions, expanding the toolkit for aryl and vinyl functionalization beyond traditional aromatic substitution mechanisms.