Synthesis and reaction of dimethyl 7-bromo-indole-2,3-dicarboxylates

Reaction of 1-(4-benzyloxyphenyl)-2-phenylhydrazine with dimethyl acetylene dicarboxylate (DMAD) gave dimethyl 5-benzyloxyindole-2,3-dicarboxylate and dimethyl indole-2,3-dicarboxylate. However, treatment of 1-(2-bromophenyl)2 -phenylhydrazine with DMAD afforded dimethyl 7-bromoindole-2,3-dicarboxylat e, exclusively. In a similar manner, dimethyl 7-bromo-5-methoxyindole-2,3-d icarboxylate was also obtained from 1-(2-bromo-4-methoxyphenyl)-2phenylhydr azine. The bromo group of dimethyl 7-bromoindole-2,3-dicarboxylate was conv erted to an 1-ethoxyvinyl or vinyl group by treatment with tributyl-(1-etho xyvinyl)tin or tributyl(vinyl)tin in the presence of a Pd(O) catalyst.