Photo-induced Wolff Rearrangement of 2-Aryl-3-diazoquinolin-4(3H)-ones to 2-Aryl-1H-indole-3-carboxylates in Flow

An effective approach was developed to the synthesis of 2-aryl-1H-indole-3-carboxylates based on photo-induced Wolff rearrangement of 2-aryl-3-diazoquinolin-4(3H)-ones. The process was implemented in flow mode under UV LED irradiation (λmax = 365 nm) with high preparative yields. Photochemical and thermal pathways for substrate activation were compared. The feasibility of applying the proposed approach to the synthesis of 3-aryl-1H-indole-2-carboxylates and 3,5-diaryl-1H-pyrrole-2-carboxylates was studied. The photophysical properties of the obtained compounds were described. Among them, fluorophores emitting at the UVA/visible boundary with a fluorescence quantum yield of up to 0.46 in solution were revealed.