1,4-Dihydropyrrolo[3,2-]pyrroles with Two Embedded Heptagons via Alkyne Annulation.

Drastic changes to the character of the acidic catalyst enable the reversal of the double alkyne benzannulation reaction output. In the presence of a strong Brønsted acid, 1,4-dihydropyrrolopyrroles undergo transformation which results in the formation of two 7-membered rings. Computational studies imply that the thermodynamically unfavored 7-membered ring is forged via the kinetically favored attack of a protonated alkyne at the position 3a of pyrrolopyrrole followed by a 1,2-vinyl shift.