Nitrobenzenesulfonyl

Nitrobenzenesulfonyl refers to the nitro-substituted benzenesulfonyl fragment used as a protecting group for amines in organic synthesis. The most common variant is the 2-nitrobenzenesulfonyl group, known as the nosyl group (Nos or Ns), which is installed on amines to form a sulfonamide and can later be removed to reveal the free amine.

Structure and properties: The group consists of a benzene ring bearing a nitro substituent and a sulfonyl linkage to the target amine. The nitro group is typically at the ortho position relative to the sulfonyl group, making the nosyl group highly electron-withdrawing. This withdrawal stabilizes the sulfonamide and can influence the reactivity and selectivity of subsequent transformations. Nosyl derivatives are usually solid and can be used in various solvent systems during protection steps.

Preparation: Nosyl chloride, the common reagent for installing the nosyl group, is prepared from 2-nitrobenzenesulfonic acid by conversion with agents such as thionyl chloride or oxalyl chloride. The NosCl reagent then reacts with amines in the presence of a base to form the nosyl-protected amine.

Uses: The nosyl group is widely used to protect amines during multi-step organic syntheses, including peptide synthesis and natural product synthesis. It is valued for its stability under many conditions and its relatively selective removal.

Removal: Desulfonylation of nosyl-protected amines can be achieved by nucleophilic desulfonylation using thiolate or other nucleophiles, or by reductive methods under specific conditions. The choice of method depends on the substrate and other protecting groups present.

Safety: Nosyl reagents and related nitro compounds are irritants and can be hazardous. Reactions should be conducted in a well-ventilated area with appropriate personal protective equipment and proper waste handling.