Two Approaches in the Synthesis of Planar Chiral Azinylferrocenes

Two synthetic routes to the chiral azinylferrocenes (CAFs) 5 and 15, key intermediates for the synthesis of new enantiomerically enriched P,N-ligands, have been compared. The first approach is based on the palladium-catalyzed cross-coupling reaction of halogenated azines with organozinc derivatives of ferrocenes (the Negishi reaction). The second approach exploits a new synthetic methodology, which provides a shorter pathway, through the direct C-H functionalization of aromatics by the C-C coupling of halogen-free (hetero)arenes with lithium ferrocenes bearing stereogenic C and S atoms. The palladium complexes of P,N-ligands have been used as catalysts for the Tsuji-Trost reaction, which proceeds with high enantioselectivity to give allylic substitution products in good yields.