Lewis and Brønsted Acid Induced (3 + 2)-Annulation of Donor–Acceptor Cyclopropanes to Alkynes: Indene Assembly

(3 + 2)-Annulation of donor–acceptor cyclopropanes to alkynes induced by both Lewis and Brønsted acids has been developed. The reaction provides a rapid approach to functionalized indenes displaying intense visible emission (λ<sub>max</sub> = 430 nm, Φ = 0.28–0.34).