Novel Domino Approach to Fluorescent Pyrimido[1,6-a]indolones

Easily accessible N-ethoxycarbonyl-2-alkynylindoles undergo, in the presence of primary aryl amines and under TiCl4/t-BuNH2 catalysis, domino hydroamination–annulation reactions giving rise to pyrimido[1,6-a]indolones in good to excellent yields. The reaction involves an initial highly regio- and chemoselective hydroamination reaction. The obtained compounds show interesting fluorescence properties and could represent a new class of useful markers for bioanalytical purpose