A convenient access to 1,3-disubstituted furo[3,4-b]indoles by acid ion-exchange resin-catalyzed furan formation

Efficient synthesis of furo[3,4-b]indoles starting from the corresponding indole is reported. The first route involves derivatization, protection, and deprotection steps, which stretch the syntheses. The second method provides a shorter and more efficient strategy to accessing the furoindole. The innovation starts with alkylation at C-2 of the indole presenting at the C-3 position a ketone-acetal, followed by the cycloaromatization catalyzed by polymeric ion-exchange resins. The second route represents a significant improvement over other methods previously described.