随着时代的发展，减少化学化工行业对环境造成的影响日益受到重视，“绿色化学”思想广泛渗透于当今的化学研究中。可见光氧化还原催化凭借其温和高效的独特优势在自由基反应中被广泛应用，是国内外研究的热点。C–X键的脱卤偶联和还原在有机合成中扮演着极为重要的角色。在过去的十几年里，借助可见光氧化还原催化来实现C–X键的脱卤及其官能团化吸引了众多化学家的兴趣和关注。论文介绍了通过可见光催化实现的新型自由基环化及脱卤还原两项工作。

通过可见光催化的手段实现了丙烯酰苯胺与偕溴代硝基烃的自由基环化反应，成功制备了一系列2-吲哚酮化合物。它们是多种天然产物和药物的重要中间体，在药物化学中的应用十分广泛。通过实验发现，可见光诱导生成α-硝基烷基自由基是启动反应的关键步骤。在碳酸银存在的条件下，通过fac-Ir(ppy)₃催化反应，在无水丙酮作溶剂时收率最高。该方法对偕溴代硝基环丁烷类的底物与丙烯酰苯胺的环化反应更为适用，为构建不同结构且含有1-硝基环丁基结构的2-吲哚酮类化合物提供了参考。克级反应及底物拓展体现了新方法较好的实用性。通过自由基捕获、Stern–Volmer磷光猝灭及XRD粉末衍射实验对反应的机理进行了推测。在光催化反应产物的衍生实验中，以较高收率得到了含有1-氨基环丁基结构的2-吲哚酮及六氢吡咯并吲哚啉产物，初步显示了这些产物的应用价值。

论文的另一部分工作，初步研究了在可见光催化下偕二溴代环丙烷的单脱溴还原反应。在合成了一些光催化剂后，通过条件筛选发现，在甲酸和三乙胺共同存在的条件下，用395 nm的紫光照射，10-苯基吩噻嗪 (PTH) 能有效催化该反应。芳基或烷基取代、螺环或并环结构的偕二溴代环丙烷都能被成功还原得到单溴环丙烷，收率优秀。关于偕二溴代环丙烷脱溴偶联的工作需要进一步探索。

With the progress of the times, reducing the environmental impact of the chemical industry is receiving increasing attention, and the concept of “green chemistry” is pervasive in modern chemical research. Photoredox catalysis, characteristic of mild conditions and high efficiency, has been widely applied in radical reactions, and emerges as a hot topic worldwide. Dehalogenative coupling and reductive dehalogenation reactions involving C–X bond play an important role in organic synthesis. In the past decade, delaogenation and functionalization of C–X bond via photoredox catalysis attracted the interest and attention from many chemists. In this thesis, novel radical cyclizations and reductive dehalogenations realized by visible light photocatalysis are reported.

Visible light induced radical cyclizations of acrylanilides with gem-bromonitroalkanes were accomplished, and a series of 2-oxindoles were prepared successfully, which are important intermediates for many natural products and pharmaceutical compounds, and are widely applied in medicinal chemistry. Through the experiments, we found that visible light induced generation of α-nitroalkyl radical was a key step to initiate the whole reactions. In the presence of Ag₂CO₃ and under blue light irradiation, the best yield was obtained in acetone when fac-Ir(ppy)₃ was used as the photocatalyst. The new protocol is especially suitable for the reactions of gem-bromonitrocyclobutane with acrylamides, and paves a new way for the construction of various 2-oxindoles bearing a 1-nitrocyclobutyl moiety. The practicality of our new method was demonstrated by a gram-scale preparation and substrate expansion reactions. The mechanism of the reaction was speculated by radical-trapping, Stern–Volmer luminescence quenching and powder X-ray diffraction experiments. Besides, derivatizations of a product from the photocatalytic reaction gave a 2-oxindole bearing a 1-aminocyclobutyl structure and a hexahydropyrroloindole derivative in high yields, implying values of practical applications.

In another part of this thesis, the monodebromination of gem-dibromocyclopropanes via visible light photocatalysis was reported. After synthesizing several photocatalysts and screening of the reaction conditions, it was found that 10-phenylphenothiazine (PTH) could effectively catalyze the reactions in the presence of formic acid and triethylamine under irradiation of 395 nm purple light. Reductions of gem-dibromocyclopropanes bearing aryl or alkyl substituent, or spirocyclic or fused-ring structure successfully delivered the monobromocyclopropanes in excellent yields. Further work on the debrominative couplings of gem-dibromocyclopropanes is underway.