Application of transmetalation to the synthesis of planar chiral and chiral-at-metal iridacycles

Diastereoselective lithiation of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline followed by addition of HgCl2 resulted in the formation by transmetallation of an (S,S_p)-configured mercury substituted complex. Addition to this of [Cp*IrCl2]2 and tetrabutylammonium chloride resulted in a second transmetallation reaction and formation of an (S,Sp,RIr)-configured chloride-substituted half-sandwich iridacycle as exclusively a single diastereoisomer. By reversing the lithiation diastereoselectivity by use of a deuterium blocking group an alternative (S,R_p,S_Ir)-configured iridacycle was synthesised similarly. Use of (R)-Ugi’s amine as substrate in the lithiation/double transmetallation sequence gave a (R,S_p,S_Ir)-configured half-sandwich iridacycle, complexes of this type being previously unavailable by direct cycloiridation. Lithium to gold transmetallation was also demonstrated with the synthesis of an (S,Sp)-configured Au(I) ferrocenyloxazoline derivative. Use of the (S,R_p,S_Ir)-iridacycle as a catalyst for the formation of a chiral product by reductive amination with azeotropic HCO₂H/NEt₃ resulted in a racemate.