P(III)-Chirogenic Phosphinite Building Blocks by Stereospecific N→O Phosphinyl Migration

In the recent past, the chirality borne by a phosphorus center has aroused growing interest in many fields, and the development of new methodologies, notably using inexpensive reagents and simple experimental conditions, has become topical. An efficient stereoselective synthesis of P-chirogenic phosphinites useful as chiral phosphorus building blocks is herein described thanks to a new intramolecular phosphorus rearrangement based on P*(III)-phosphinyl N→O migration. This rearrangement was performed by heating at 50 °C aminophosphine-boranes, easily prepared from chiral amino alcohols, with DABCO in toluene overnight. Twenty-seven P-chirogenic phosphinites and borane complexes were thus prepared in yields up to 89%. The crude P*(III)-phosphinites were in situ used in stereoselective synthesis of P-chirogenic aminophosphine-phosphinites, phosphinothioates, sec- and tert-phosphine-oxides, and mono- and diphosphines in overall yields ranging from 28 to 89% and with e.e. up to 99%. Twenty-one X-ray structures of P-chirogenic compounds were established, allowing us to attribute undoubtedly their absolute configuration and the stereochemistry of the reactions. Finally, new ferrocenyl-bridged diphosphine ligands synthesized from P*(III)-chirogenic diphosphinites were tested in asymmetric metal-catalyzed reactions, providing enantioselectivities up to 95% e.e. in allylation of α-naphthylmethylamine at room temperature. To conclude, this rearrangement opens up an efficient new way for the stereoselective synthesis of numerous classes of P-chirogenic phosphorus compounds, notably bearing bulky substituents.