Tert‐Butylnitrite Mediated Regioselective C(sp2)−3 Nitration of Substituted 4‐Quinolones and Its Late‐stage Manipulations

A unified approach for the regioselective C(sp²)3-H nitration has been developed to expedite the access of nitro derivatives of 4-quinolones in presence of t-BuONO (nitrating agent)/TEMPO. The protocol tolerated diverse functional groups and substitution patterns, affording the target products in good yields. Synthetic utility of this transformation has been illuminated via the formation aminated quinolones along with their photophysical studies.

Abstract

A novel and eco-friendly technique for the synthesis of C-3 nitro derivatives of 4-quinolones via the regioselective C(sp²)−H bond functionalization employing tert-butyl nitrite as nitrating agent in presence of TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl)oxyl] as an oxidant is unfolded herein. The protocol is scalable as well as high yielding with wide substrate scope and broad functional group tolerance. In-depth mechanistic investigations revealed that the reaction occurred through a free radical pathway. The nitro derivatives of 4-quinlones were selectively reduced to corresponding aminated 4-quinolones. Finally, the photophysical properties of synthesized amine derivatives were also investigated, and some of them showed good fluorescence properties.

Zum Volltext