Abstract
The functionalization of aryl C(sp2)−H bonds is a useful strategy for the late‐stage modification of biologically active molecules, especially for the regioselective introduction of azole heterocycles to prepare medicinally‐relevant compounds. Herein, we describe a practical photocatalytic transformation using a mesoporous carbon nitride (mpg‐CN x ) photocatalyst, which enables the efficient azolation of various arenes through direct oxidation. The method exhibits a broad substrate scope and is amenable to the late‐stage functionalization of several pharmaceuticals. Due to the heterogeneous nature and high photocatalytic stability of mpg‐CN x , the catalyst can be easily recovered and reused leading to greener and more sustainable routes, using either batch or flow processing, to prepare these important compounds of interest in pharmaceutical and agrochemical research.
Highlights
The ability to functionalize organic molecules is the central tenet of synthetic organic chemistry.[1]
The mpg-CNx photocatalyst was synthesized as previously reported by heating cyanamide as a precursor with silica as a hard template in air at 550 °C for 4 h, followed by silica etching using aqueous ammonium difluoride.[16b]. The material was characterized by powder X-ray diffraction, attenuated total reflectance infrared (ATR-IR), UV/Vis diffuse reflection spectroscopy (DRS), and scanning electron microscopy (SEM) to confirm the composition and morphology of mpg-CNx (Figure 1)
After an extensive evaluation of different reaction conditions, we identified optimal reaction conditions outlined in Table 1, entry 1
Summary
The ability to functionalize organic molecules is the central tenet of synthetic organic chemistry.[1]. Nicewicz and co-workers have shown that such a strategy can be used for the site-selective C(sp2)À H amination of arenes with azoles.[12] A photoelectrocatalytic approach was developed by Hu and co-workers using hematite as photoanode and allowed to avoid the use of homogeneous photocatalysts.[13] Recently, Wang, König and co-workers developed a metal-free semiconductor strategy using hexagonal boron carbon nitride as a photocatalyst.[14] Despite these seminal advances, a general protocol displaying a broad substrate scope and using an easy-to-recover photocatalyst remains a challenge. The photocatalyst can be loaded in a packed-bed reactor, which allows easy separation of the product from the photocatalyst and enables scale-up as well as higher-throughput of the targeted transformation in flow
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