Aryne-involved α-C(sp3)–H arylation of 4-aminopyrazolones via two distinct systems: dual phase-transfer catalysis and ultraviolet photochemistry

Abstract

Direct α-C(sp³)–H arylation of 4-aminopyrazolones involving arynes, enabled by dual phase-transfer catalysis and ultraviolet irradiation, has been developed. The dual phase-transfer catalytic pathway powered by triaminocyclopropenium salts gave rise to the generation of structurally diverse 4-amino-4-arylpyrazolones in moderate to excellent yields, while the photochemical protocol furnished the products in moderate yields. Notably, these products are tentatively proposed as candidates for carbamate pesticides based on the preliminary structural analysis. The synthetic potentials of the methods were shown by gram-scale reactions, and the possibilities for greater structural diversity of the product were highlighted by derivatizations. The results of control experiments indicated that the timely capture of the transient arynes by the activated 4-aminopyrazolone nucleophiles is the key to the success of the reactions.