Application of Transmetalation to the Synthesis of Planar Chiral and Chiral-at-Metal Iridacycles

Abstract

Diastereoselective lithiation of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline, followed by addition of HgCl2, resulted in the formation by transmetalation of an (S,Sp)-configured mercury substituted complex. Addition to this of [Cp*IrCl2]2 and tetrabutylammonium chloride resulted in a second transmetalation 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,Rp,SIr)-configured iridacycle was synthesized similarly. Use of (R)-Ugi’s amine as substrate in the lithiation/double transmetalation sequence gave an (R,Sp,SIr)-configured half-sandwich iridacycle, complexes of this type being previously unavailable by direct cycloiridation. Lithium to gold transmetalation was also demonstrated with the synthesis of an (S,Sp)-configured Au(I) ferrocenyloxazoline derivative. Use of the (S,Rp,SIr)-iridacycle as a catalyst for the fo...