Lewis acid‐activated ambiphilic reactivity on N‐furan‐2‐ethynylanilines toward the synthesis of cyclopenta[ <i>b</i> ]indoles

Abstract A novel efficient method provides sustainable synthetic access to multi‐substituted cyclopenta[ b ]indole derivatives is reported. Building upon established synthetic protocols, which often employ noble metal catalysts and demanding conditions, this strategy introduces a molecular designed N‐furan aniline for cost‐effective and environmentally conscious alternative. The strategy utilizes stoichiometric, readily available aluminum chloride (AlCl 3 ) under mild conditions, providing broad access to diverse cyclopenta[ b ]indole derivatives. The proposed mechanism shows that Lewis acid activation triggers a selective ring‐opening of the furan, which is crucial for forming the cyclopenta[ b ]indole framework. The demonstrated synthetic utility, including the facile conversion of the scaffold into diazo and tosylhydrazone derivatives, underscores the potential of this methodology for constructing diverse, complex bioactive molecules, such as those related to Etrasimod and Fischerindole L.