Chlorosulfonic acid-mediated cyclization of 4-phenyl-3-isocoumarincarboxylic acids and 4-phenyl-3-isoquinolinonecarboxylic acids: an efficient synthesis of 3-oxoindeno[2,1-c]isocoumarins and 3-oxoindeno[2,1-c]isoquinolinones

A highly efficient and clean method has been developed for the synthesis of 3-oxoindeno[2,1-c]isocoumarins and 3-oxoindeno[2,1-c]isoquinolinones from 4-phenyl-3-isocoumarincarboxylic acids and 4-phenyl-3-isoquinolinonecarboxylic acids, respectively.