Enantioselective synthesis of planar chiral azaferrocenes via chiral ligand-mediated ring- and lateral-lithiations

Lithiation of 1′,2′,3′,4′,5′-pentamethylazaferrocene (1) with sec-BuLi/(−)-sparteine (3) in Et2O at −78°C followed by quenching with electrophiles gave the ring-substituted products 2 in 74–81% ee. On the other hand, lithiation of 1′,2,2′,3′,4′,5,5′-heptamethylazaferrocene (6) with sec-BuLi in the presence of S-valine-derived bis(oxazoline) 5 in Et2O at −55°C and subsequent reaction with electrophiles afforded the laterally functionalized products 7 in excellent enantioselectivity (96–99% ee).