Kinetic and mechanistic studies of the Staudinger reduction: On the chemistry of aryl phosphazides

• Published in: Journal of physical organic chemistry Vol. 36; no. 2
• Main Authors: Corrigan, Samantha Y., Poole, James S.
• Format: Journal Article
• Language: English
• Published: Bognor Regis Wiley Subscription Services, Inc 01.02.2023
• Subjects: aryl azides; Hydrolysis; NMR; Nuclear magnetic resonance; phosphazides; product analysis; Reaction mechanisms; Reduction; Staudinger reduction
• ISSN: 0894-3230; 1099-1395
• DOI: 10.1002/poc.4442

The Staudinger reduction of heteroaryl azides containing an N‐oxide moiety with triphenylphosphine in mixed aqueous/THF solutions yields a mixture of amine and iminophosphorane products. A product analysis study using a combination of 1H and 31P NMR spectroscopic techniques indicates that in these systems, even under mild conditions, the amine product is generated, not from the hydrolysis of the iminophosphorane as expected from the standard reaction mechanism, but via hydrolysis of the phosphazide intermediate. The amount of amine generated is dependent on the structure of the starting azides, the composition of solvent, and the reaction conditions. The possible mechanisms of amine formation under acidic, neutral, and basic conditions are discussed. A combined 1H and 31P NMR analytical study is described for the reaction of aryl azides containing an N‐oxide moiety with triphenylphosphine—the Staudinger reduction. The formation of the amine is a favorable process and proceeds via the hydrolysis of the phosphazide intermediate.