Diastereoselectiveortho-Metalation of a Chiral Ferrocenylphosphonic Diamide and Its Organotin Derivatives

Abstract

The syntheses of the enantiopure ferrocenylphosphonic diamide (3aR,7aR)-2-ferrocenyl-3a,4,5,6,7,7a-octahydro-1,3-dimethyl-1,3,2-benzodiazaphosphole 2-oxide ((R,R)-FcP(O)(DMCDA), (R,R)-1) and its enantiomer (S,S)-FcP(O)(DMCDA) ((S,S)-1) are reported. Their ortho lithiation and subsequent treatment with Ph3SnCl selectively provided the corresponding tetraorganotin derivatives FcP(O)(DMCDA)SnPh3 ((R,R,RP)-2 and (S,S,SP)-2) in a diastereoselective ratio of 88:12. The absolute configuration of the major diastereomer was confirmed by single-crystal X-ray diffraction analysis. DFT calculations revealed that kinetic effects of the lithiation step cause the high diastereoselectivity of the formation of (R,R,RP)-2. Further functionalization of (R,R,RP)-2 with elemental iodine gave the enantiopure organotin iodide derivatives FcP(O)(DMCDA)SnInPh3–n ((R,R,RP)-3:, n = 1; (R,R,RP)-4, n = 2, (R,R,RP)-5, n = 3). The triorganotin fluoride FcP(O)(DMCDA)SnFPh2 ((R,R,RP)-6) was obtained by the reaction of (R,R,RP)-3 in dichloromethane with aqueous KF solution. The reaction of the compound (R,R,RP)-3 with silver triflate gave the R,R,RP-configurated triorganotin triflate FcP(O)(DMCDA)SnPh2(OTf) (7), which exists as a contact ion pair in the solid state and shows dynamic behavior in solution. The reaction of 7 with Ph3PO afforded the corresponding organotin salt [FcP(O)(DMCDA)SnPh2(OPPh3)][OTf] ((R,R,RP)-8).