Functionalization of metal-protected chiral phosphines via simple organic transformations

Abstract

With metal as protection, the introduction of functionalities on coordinated chiral phosphines using organic transformations was demonstrated. Bis(diphenylphosphino)-substituted oxa- and azanorboraene metal complexes were subjected to a series of organic transformations including hydrogenation, hydroboration, electrophilic addition, and dihydroxylation reactions. Hydrogenation of the oxanorbornene double bond stabilizes the free diphosphino-substituted oxanorbornene ligand, which is otherwise prone to the retro-cycloaddition reaction. Hydroboration of the oxanorbornenic double bond using borane, followed by oxidation with alkaline hydrogen peroxide, generated two regioisomeric products with the introduction of a hydroxy group at the exo position. However, regioselective hydroboration could be achieved with the use of 9-BBN as the hydroborating agent. Stereoselective electrophilic addition of the oxanorbornenic double bond with phenylselenenyl chloride resulted in the formation of a sole antiaddition product. Subsequent oxidative syn-elimination of the resultant selenide product was also shown to proceed regioselectively to give the vinyl chloride complex. Dihydroxylation of the oxa- and azanorbornenic double bond with osmium tetraoxide proceeded stereoselectively with the introduction of two hydroxy group at the exo positions. Liberation of the functionalized chiral phosphine ligands from the metal complexes was also illustrated. © 2006 American Chemical Society.