Gold-catalyzed cascade reactions of 4H-furo[3,2-b]indoles with propargyl esters: synthesis of 2-alkenylidene-3-oxoindolines

Abstract

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 the initial formation of a gold-carbene species via cationic gold(I) catalysed 1,2-acyloxy migration of properly substituted propargyl esters followed by the addition of gold-carbene to furoindole and successive furan ring-opening affording the final products. The obtained compounds contain an extended π-system linked at the C2 of the indolin-3-ones; they show intense colouration (from yellow to purple) and are characterised by UV measurements.