Staudinger ligation

Staudinger reaction
Named after	Hermann Staudinger
Reaction type	Organic redox reaction
Identifiers
Organic Chemistry Portal	staudinger-reaction
RSC ontology ID	RXNO:0000066

The Staudinger reaction is a chemical reaction of an azide with a phosphine or phosphite produces an iminophosphorane. The reaction was discovered by and named after Hermann Staudinger. The reaction follows this stoichiometry:

The Staudinger reduction is conducted in two steps. First phosphine imine-forming reaction is conducted involving treatment of the azide with the phosphine. The intermediate, e.g. triphenylphosphine phenylimide, is then subjected to hydrolysis to produce a phosphine oxide and an amine:

The overall conversion is a mild method of reducing an azide to an amine. Triphenylphosphine is commonly used as the reducing agent, yielding triphenylphosphine oxide as the side product in addition to the amine. An example of a Staudinger reduction is the organic synthesis of this pinwheel compound:

The reaction mechanism centers around the formation of an iminophosphorane through nucleophilic addition of the phosphine at the terminal nitrogen atom of the azide and expulsion of nitrogen. This intermediate is then hydrolyzed in the second step to the amine and triphenylphosphine oxide

Of interest in chemical biology research, the Staudinger ligation is a modification of the classical Staudinger reaction in which an electrophilic trap (usually a methyl ester) is placed on the triaryl phosphine. In aqueous media, the aza-ylide intermediate rearranges, to produce an amide linkage and the phosphine oxide, and is so named the Staudinger ligation because it ligates two molecules together, whereas in the classical Staudinger reaction, the two products are not covalently linked after hydrolysis. A traceless version of the reaction leaves behind no residual atoms.

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