ABSTRACT
This review summarizes the literature regarding the use of phosphine oxides as catalysts and precatalysts. The early sections focus on the use of phosphine oxide catalysts in: (1) carbon–nitrogen double bond-forming transformations involving phosphinimide intermediates, such as carbodiimide synthesis, and aza-Wittig reactions, (2) Lewis base-mediated nucleophilic addition reactions to aldehydes, ketones, imines, and epoxides, (3) reduction reactions, and (4) metal-halogen exchange reactions. Another section discusses the use of phosphine oxides for the in situ generation of halophosphonium salts, which can be used catalytically in Appel and related reactions. The last sections are centered on reaction systems involving P(III)/P(V) cycling strategies in which a generated phosphine oxide reaction by-product is reduced in situ to regenerate a phosphine catalyst. This general concept has been applied to numerous reactions that traditionally use phosphine reagents and produce phosphine oxide by-products, such as Wittig and Staudinger ligation reactions.
