Ferrocenyl induced one-pot synthesis of 3,3′-ferrocenylbiindoles

When we used 2-ferrocenethynylaniline (1a) as reactant and NaAuCl4·2H2O (5%) as catalyst to prepare 2-ferrocenylindole (2a), we were surprised to find that 3,3′-ferrocenylbiindole (3a) was obtained...