Two-Step Synthesis of π-Expanded Maleimides from 3,4-Diphenylfuran-2(5H)-ones.

An efficient two-step synthesis of π-expanded maleimide derivatives was reported, which proceeded via a photoinduced dehydrogenative annulation of 3,4-diphenylfuran-2(5H)-ones in EtOH at room temperature for 5 h under an argon atmosphere, followed by interaction with primary amine in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene and O2. The synthesis of highly conjugated maleimides demonstrated that 3,4-diphenylfuran-2(5H)-ones were useful precursors for synthesis of π-expanded lactones and π-expanded maleimides with no need of a transition-metal catalyst. Additionally, the fluorescent properties of the highly conjugated maleimides were characterized and were found to possess high fluorescence quantum yields in dichloromethane solution.