Approaches to the synthesis of 1H-[1]benzothieno[2,3-d]imidazoles and thieno[2,3-d]imidazoles

Photolysis of three NN-disubstituted 3-amino-2-nitrobenzo[b]thiophen derivatives gave mixtures of 2-nitro-benzo[b]thiophen-3-ol and benzo[b]thiophen-2,3-quinone2-mono-oxime. 3-Benzylamino-2-nitrobenzo[b]thiophen was cyclised to an N-oxide under basic conditions. This N-oxide was converted into a benzoyloxy-derivative and was also deoxygenated to give 2-phenyl[1]benzothieno[2,3-d]imidazole. Reduction of 3-formamido-2-nitrobenzo[b] thiophen gave [1]benzothieno[2,3-d]imidazol-2(3H)-one in low yield. Efforts to extend these cyclisation processes to analogous thiophen derivatives did not succeed.