Gold-Catalyzed Cascade Reactions of 4H‑Furo[3,2‑b]indoles with Propargyl Esters: Synthesis of 2-Alkenylidene-3-oxoindolines

2-alkenyliden-indolin-3-ones were synthesised in high yields via a cascade reaction between 4H‑furo[3,2‑b]indoles and propargyl esters. The cascade sequence involves initial formation of a gold-carbene specie via cationic gold(I) catalysed 1,2-acyloxy migration of properly substituted propargyl esters followed by gold-carbene to furoindole addition and successive furan ring-opening affording the final products. The obtained compounds contain an extended -system linked at the C2 of the indolin-3-ones, they are characterised by intense colouration (from yellow to purple) and were characterised by UV mesearurements.