Revealing the Activity of π-Acid Catalysts using a 7-Alkynyl Cycloheptatriene.

A compound that isomerizes into distinct products depending on the particular Lewis acid or Brønsted acid catalyst used is disclosed. One product can only be obtained with the softest π-acids, such as Au, Pt, Ga, or In complexes. Another is formed only with harder π-acids incorporating Ag or Cu salts. The formation of the third category requires even harder π-acids or protons. This simple benchmark reaction allows for prediction of the category of transformations that can be catalyzed by a new complex. It also informs whether protons have been unintentionally generated in the reaction mixture.