Phosphorylation of α-Haloimines: P-C vs. P-N Bond Formation

The chemoselectivity of reactions between α-haloimines - compounds containing a Hal-C-C=N-skeleton - and nucleophilic phosphorus derivatives are discussed systematically. The synthetic potentialities, as well as possible mechanistic pathways of this currently developing field of organophosphorus chemistry are considered. Phosphorylation of the α-haloimines leads mainly to C- or N-phosphorylated compounds as the final products, the selectivity being dependent on the type of halogen, substituents at the imine carbon and nitrogen atoms, and on the nature of phosphorus reagent. The main factors controlling regio- and stereoselectivity are elucidated. A series of novel theoretically and preparatively important transformations have also been illustrated; i.e., new diad rearrangements involving the N→C and C→N transfer of a sulfonyl or a phosphoryl group, the unusual acylation of the electrophilic imine carbon atom by tervalent phosphorus isocyanates, and others. Variety of transformations is connected with the possible participation of C=N bond, halogen atoms or N-substituents, in reactions involving the Hal-C-C=N- arrangement. The use of haloimines as versatile building blocks for synthesis of practically promising functionalized aminophosphonates, bisphosphonates, and phosphorus analogs of dehydro aminoacids, etc., is demonstrated.