Highly Convergent Synthesis of Intensively Blue Emissive Furo[2,3-c]isoquinolines by a Palladium-catalyzed Cyclization Cascade of Unsaturated Ugi Products

A convergent and diversity-oriented approach to the unusual furo[2,3-c]isoquinoline scaffold is presented. This serendipity-driven approach is characterized by an Ugi multicomponent reaction, which gives the substrate for a palladium-catalyzed insertion-alkynylation-cycloisomerization cascade to provide the furo[2,3-c]isoquinolines in moderate to high yield. Upon UV excitation, all representatives are intensively blue luminescent, as observed by the naked eye, and quantitative fluorescence spectroscopy reveals a considerable effect of the substitution pattern on the quantum yields. The electronic structure is semiquantitatively rationalized by DFT and time-dependent DFT calculations.