Dihydrocarbazoles were synthesized through a novel [4+2] annulation of donor-acceptor cyclopropanes (DACs) to indoles. This reaction was performed in ethanol by using para-toluenesulfonic acid as catalyst. Mechanism of this reaction might involve the following three steps: (i) an electrophilic ring-opening reaction of the DACs with indoles, in which C3 position of indole acts as a nucleophilic site, (ii) an intramolecular dehydration induced ring-closing reaction occurs that offers a spiro intermediate, and (iii) a following 1,2-migration which leading to a dihydrocarbazole scaffold. Otherwise, dihydroisoindole can also be constructed by replacing the indole component with pyrrole as nucleophile.