De Novo Protocol for the Construction of Benzo[ a ]fluorenes via Nitrile/Alkene Activation.

Unprecedented chemo- and regioselective synthesis of benzo[ a ]fluorenes and naphthamide-substituted benzo[ a ]fluorenes were constructed from the reaction of ( E )-2-aroyl-3-(2-(arylalkynes/alkenes)aryl)acrylonitrile scaffolds under metal-free conditions via the activation of nitriles and alkenes, respectively. A tentative reaction mechanism was proposed for this homofunctionalization of nitriles. Control experiments showed that the reaction proceeds via selective nitrile or alkene protonation, depending upon the substrates. Additionally, we demonstrated an alternative expeditious route for the synthesis of disubstituted benzo[ a ]fluorenes in the presence of TfOH alone.