Access to Thiophene and 1H‑Pyrrole via Amine-Initiated (3 + 2) Annulation and Aromatization Cascade Reaction of β′-Acetoxy Allenoate and 1,2-Bisnucleophile

The amine-catalyzed cascade (3 + 2) annulation and aromatization sequence between β′-acetoxy allenoates and 1,2-bisnucleophiles has been developed. When 1,4-dithane-2,5-diol is used as the bisnucleophile partner, the corresponding reaction affords fully substituted thiophene-2-carbaldehyde, which might proceed via the amine-catalyzed (3 + 2) annulation and subsequent oxidative aromatization. The reaction protocol is also applicable to a 2-tosylamino-carbonyl bisnucleophile, wherein the (3 + 2) annulation is followed by 1,2-elimination of a tosyl group and isomerization to give a 1H-pyrrole product.