Direct Transition-Metal Free Benzene C-H Functionalization by Intramolecular Non-Nitroarene Nucleophilic Aromatic Substitution of Hydrogen to Diverse AIEgens.

Abstract

Direct C(sp2 )-H functionalization through nitroarene-triggered nucleophilic aromatic substitution of hydrogen (SNArH ) has attracted growing attention, owing to its high efficiency and low carbon footprint. In this study, non-nitro-group-assisted SN ArH has been developed for direct benzene functionalization in one pot under mild conditions. The electron-withdrawing carbonyl group and the halide or trifluoromethyl group on the phenyl ring enable the σH adduct formation to fulfill the intramolecular C(sp2 )-C(sp3 ) bond construction. Notably, the cyano group serves as both the electron-withdrawing group to activate the C(sp3 )-H bond and the leaving group to fulfill the β-elimination. Three series of pyrrolo[1,2-b]isoquinolinones, as well as unexpected rearrangement products 3-(1H-pyrrol-2-yl)-1H-inden-1-ones are regioselectively obtained through a simple and efficient base-catalyzed one-pot strategy. Mechanistic studies indicate that the σH adduct from carbanion addition to hydrogen serves as the sole intermediate for all of the aforementioned transformations. These molecules show intense luminescence and the subsequent one-step structural modification results in the aggregation-induced emission (AIE) derivatives with redshifted full-color tunable fluorescence, large Stokes shifts, and good quantum yields. Further living cell imaging investigations suggest their potential application as specific bioprobes for lipid droplet localization and visualization.