Access to Enantiomerically Pure P -Chiral 1-Phosphanorbornane Silyl Ethers
Sulfur-protected enantiopure P -chiral 1-phosphanorbornane silyl ethers 5a , b are obtained in high yields via the reaction of the hydroxy group of P -chiral 1-phosphanorbornane alcohol 4 with tert -butyldimethylsilyl chloride (TBDMSCl) and triphenylsilyl chloride (TPSCl). The corresponding optically pure silyl ethers 5a , b are purified via crystallization and fully structurally characterized. Desulfurization with excess Raney nickel gives access to bulky monodentate enantiopure phosphorus(III) 1-phosphanorbornane silyl ethers 6a , b which are subsequently applied as ligands in iridium-catalyzed asymmetric hydrogenation of a prochiral ketone and enamide. Better activity and selectivity were observed in the latter case.