1,4-Dihydropyrrolo[3,2‑<i>b</i>]pyrroles\nwith Two Embedded Heptagons via Alkyne Annulation

Drastic changes to\nthe character of the acidic catalyst\nenable\nthe reversal of the double alkyne benzannulation reaction output.\nIn the presence of a strong Brønsted acid, 1,4-dihydropyrrolopyrroles\nundergo transformation which results in the formation of two 7-membered\nrings. Computational studies imply that the thermodynamically unfavored\n7-membered ring is forged via the kinetically favored <i>6-endo-dig</i> attack of a protonated alkyne at the position 3a of pyrrolopyrrole\nfollowed by a 1,2-vinyl shift.