Covalent Organic Frameworks: A Sustainable Photocatalyst toward Visible‐Light‐Accelerated C3 Arylation and Alkylation of Quinoxalin‐2(1H)‐ones

Abstract

A practical and scalable protocol for visible‐light‐accelerated arylation and alkylation of quinoxalin‐2(1H)‐ones with hydrazines is reported. In this protocol, a hydrazone‐based two‐dimensional covalent organic frameworks (2D‐COF‐1) was employed as the heterogeneous photocatalyst (PC). Due to its excellent photocatalytic properties, good chemical stability and heterogeneous nature, the present method exhibits high efficiency, good functional group tolerance, easy scalability and remarkable catalyst reusability. More importantly, it provides an alternative way that allows rapid access to various C3 arylated or alkylated quinoxalin‐2(1H)‐ones in a greener and sustainable manner.

Recent Advances in Photocatalytic Functionalization of Quinoxalin‐2‐ones

“…The last example on alkylation of quinoxalin-2-ones comes from Yang's research group in early 2020. [42] These researchers employed a Covalent Organic Framework (COF), [43] more specifically hydrazone based 2D-COFs previously, reported by them. [44] Using their customized two-dimensional 2D-COF-1, they can access alkylated quinoxalin-2-ones taking aliphatic hydrazines as alkyl equivalents in combination with potassium carbonate as base under the irradiation of Blue LEDs in an aero-bic heterogeneous reaction environment.…”

“…The last approach towards C-3 arylated quinoxalin-2-ones comes from the already mentioned work of Yang on the utiliza- tion of hydrazines as C-centered radical precursors. [42] In the section referred to alkylation procedures, we showed how the team of Yang used a heterogeneous system based on a COF to generate alkyl radicals from hydrazines. They were also able to extend their methodology to aromatic hydrazines in order to obtain 3-aryl-quinoxalin-2-ones in moderate to good yields (Scheme 38).…”

“…The last example on alkylation of quinoxalin‐2‐ones comes from Yang's research group in early 2020 . These researchers employed a Covalent Organic Framework (COF), more specifically hydrazone based 2D‐COFs previously, reported by them .…”

Covalent Organic Frameworks in Catalytic Organic Synthesis

“…Yang and co-workers synthesized a hydrazine-based COF (2D-COF-1, Figure 4, Table 2) to catalyze a tandem radical addition-cyclization reaction and a direct C 3 arylation and alkylation of quinoxaline-2(1H)-ones under air environment and visible light condition (Scheme 8). [46][47] Both of the reactions are traditionally carried out with radical initiators, transition-metals or organic dyes as photosensitizers. This work, however, shows us the great potential for COFs to replace homogeneous metal catalysts by introducing and tuning functional building blocks with special photoelectric properties.…”

The C3-H Bond Functionalization of Quinoxalin-2(1H)-Ones With Hypervalent Iodine(III) Reagents

“…Some bioactive molecules containing quinoxalin-2(1 H )-one skeleton, such as Compounds 1 - 3 , also show potential applications in medicinal chemistry fields (Meyer et al, 2006 ; Khattab et al, 2015 ; Qin et al, 2015 ) ( Figure 1A ). Because of their synthetic usefulness and potential biological importance, the introduction of functional groups into the C3-position of the quinoxalin-2(1 H )-ones has already become a research hotspot, and various protocols for the direct C3-H functionalization of quinoxalin-2(1 H )-ones have been reported (Ebersol et al, 2019 ; Gu et al, 2019 ; Hong et al, 2019 ; Li et al, 2019 ; Peng et al, 2019 ; Rostoll-Berenguer et al, 2019 ; Teng et al, 2019 ; Wang et al, 2019a , 2020 ; Xie et al, 2019b ; Zhao et al, 2019 ; Zheng and Studer, 2019 ; Tian et al, 2020 ; Yuan et al, 2020 ). In particular, the C3-H functionalization of quinoxalin-2(1 H )-ones involving hypervalent iodine reagents has drawn wide attention for the aforementioned advantages of hypervalent iodine reagents, mainly including arylation (Paul et al, 2017 ; Yin and Zhang, 2017 ), trifluoromethylation (Wang et al, 2018 ; Xue et al, 2019a ), alkylation (Wang et al, 2019b ; Xie et al, 2019a ; Xue et al, 2019b ; Shen et al, 2020 ), and alkoxylation (Xu et al, 2019 ; Yang et al, 2019 ) of quinoxalin-2(1 H )-ones, which provide convenient and environmentally friendly means for the synthesis of 3-substituted quinoxalinone derivatives.…”