The synthesis of isoquinolines, indoles and benzthiophen by an improved Pomeranz-Fritsch reaction, using boron trifluoride in trifluoroacetic anhydride

Pomeranz-Fritsch cyclisations are reported using a new reagent boron trifluoride-trifluoroacetic anhydride. Isoquinolines carrying 7-OMe groups have been prepared in good yields and the method extended to the formation of N-substituted indoles and of benzthiophen from the corresponding acetals. Benzofuran could not be obtained by this procedure nor could a Bischler-Napieralski type cyclisation be induced. In the latter case the aromatic ring of the starting amide was acetylated when suitably activated.