Synthesis of 4-hydroxy and 6-hydroxyindoles: a renaissance of the Bischler reaction

In the present work we studied a modified Bischler-Möhlau reaction – synthesis of indoles from benzoin and aniline. Our proposed modification of this method differs from that described earlier in that the reaction is carried out at a lower temperature, which makes it possible to improve yields and reduce formation of tarry side products. In addition, unlike the previous contradictory works, which described the preparation of a single 4-hydroxy or 6-hydroxy isomer in condensation of m-aminophenol and benzoin, we obtained both 4-hydroxy and 6-hydroxy isomers.