Indium-Catalyzed Aromative Spiro Coupling of Quinones with Oxindoles for Highly Functionalized Xanthenes as Efficient Fluorophores

A convenient and an efficient protocol for the assembly of diverse xanthenes bearing a biologically interesting oxindole nucleus is developed by utilizing the In­(III)-catalyzed spiro coupling of 1,4-benzoquinones or 1,4-naphthoquinones with oxindoles. This novel protocol proceeds via a cascade of double Michael additions and intramolecular cyclization. The synthesized compounds have potential use as fluorophores for the selective imaging of heavy metals in living cells.