Microdroplets Catalyze C(sp²)-H Nitration Reactions

Microdroplet chemistry is reforming organic synthesis in a green and sustainable manner in recent years because of the unique catalytic and redox environment at the gas-liquid interface. Nitration, an important way of introducing nitro groups, traditionally requires the use of nitric acid in large amounts under certain catalysts at high temperatures in a long duration. To address these unsustainable problems, we developed a catalyst-free microdroplet method for efficient and mild nitration due to the catalytic activity of the microdroplets. However, catalyst-free microdroplet nitration offered good conversions (maximum 61%) only at the micromolar scale. By externally introducing 1 equiv of TfOH, we achieved 53-98% yields at the molar scale from 11 (hetero)arenes with a 1.06 g h^-1 scalability. This method was characterized by short time, high conversion, wide substrate range, and gram ability, making it attractive for nitrated (hetero)arenes.