A P-chirogenic β-aminophosphine synthesis by diastereoselective reaction of the α-metallated PAMP–borane complex with benzaldimine

International audienceThe diastereoselective synthesis of a P-chirogenic β-aminophosphine ligand with carbon–carbon bond formation of the ethano bridge in a 3:1 ratio via reaction of an α-metallated P-chirogenic phosphine borane with a benzaldimine is described. The diastereoselectivity is attributed to a transition state where the lithium cation chelates the phosphine borane carbanion and the nitrogen of the imine and the attack of the C@N occurs on the face opposite to the P–B bond, due to its interaction with the antibonding P–B bond. The major diastereoisomeric β-aminophosphine borane was then separated and decomplexed into the corresponding β-aminophosphine under neutral conditions and without epimerization by heating at reflux in EtOH. This synthesis offers a short hemisynthetic route to the P-chirogenic β-P,N-ligands, by bridge formation starting from methylphosphine boranes.The diastereoselective synthesis of a P-chirogenic β-aminophosphine ligand with carbon–carbon bond formation of the ethano bridge is described in three steps, via a key reaction of the α-metallated P-chirogenic phosphine borane with a benzaldimine