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.