nosylates

Nosylates are sulfonate esters derived from p-nitrobenzenesulfonic acid, typically formed by reacting an alcohol with p-nitrobenzenesulfonyl chloride (Nos-Cl). In general, the resulting nosylate has the structure R-O-SO2-Ph-NO2, where Ph-NO2 denotes the 4-nitrobenzene ring attached to the sulfonyl group. The Nos group serves as an activated leaving group in subsequent nucleophilic substitutions, enabling conversion of alcohols into a variety of products.

Preparation and handling: The standard preparation involves treating an alcohol with Nos-Cl in the presence of a base such as pyridine or triethylamine, usually in an aprotic solvent. Nos-Cl is moisture sensitive and lachrymatory, requiring appropriate protective measures. The nosylate can be purified by conventional chromatographic methods.

Reactivity and applications: Nosylates function as leaving groups in SN2 and related transformations. The electron-withdrawing nitro substituent on the aryl ring enhances the leaving-group ability of the sulfonate, often providing good to excellent reactivity for substitution by nucleophiles such as amines, thiolates, or alkoxides. In synthetic sequences, nosylates are used to activate alcohols for nucleophilic displacement or as stepping-stones in complex molecule construction. The p-nitrobenzenesulfonyl moiety can also influence chemoselectivity in multi-step sequences and is sometimes compared with other sulfonate leaving groups such as tosylates or mesylates.

Relation to other nosyl chemistry: The term nosylate refers specifically to the O-sulfonate esters derived from p-nitrobenzenesulfonyl chloride. Separately, the nosyl (Ns) protecting group is a related concept used for amines, but that Ns group is distinct from the Nos-ester leaving groups described here.

Safety: Nos-Cl and nosylates are reactive and should be handled under appropriate safety protocols, with good ventilation and personal protective equipment.