Identification of a 4H-benz[f]indole by-product from the Friedel-Crafts-based synthesis of benzoylpyrrole calcium channel activators

9,9a-Dihydro-2,9a-dimethyl-4-oxo-4H-benz[f]indole-3-carboxylic acid, methyl ester was formed in varying amounts from the Friedel-Crafts-based synthesis of benzoylpyrrole calcium channel activators. The structure of this by-product was determined using two-dimensional long-range 1 H- 13 C heteronuclear correlated and INADEQUATE nmr techniques