The reaction of indolyl magnesium bromide with 2, 3-dibromo-N-methylmaleimide (3) in toluene leads to bisindolylmaleimides 6. In THF a monosubstitution product 5 is obtained which after protection of the indole NH-group with the Boc residue can be used to prepare unsymmetrically substituted bisindolylmaleimides, arcyriarubin B given as an example.
