A Metathesis Approach to Aromatic Heterocycles
The ring closing metathesis (RCM) reaction can be used to prepare substituted furans and pyrroles. By utilising a Pd-catalysed coupling reaction with methoxyallene, allylic alcohols and sulfonamides can be converted into substrates that are ideal precursors to ring closing metathesis. After the RCM reaction is complete, the addition of acid promotes an elimination of methanol to form the fully aromatised system. A range of different substitution patterns and functional groups are compatible with this sequence. Double allene coupling, RCM and elimination reactions are also possible and allow the formation of biaryl systems. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)