**1. Introduction**

Of late, photo-redox catalysis has been utilized as a flexible and demanding synthetic protocol in the realm of modern organic chemistry due to its environmental friendliness and sustainability [1]. This visible-light-driven protocol essentially affords a large number of nitrogen centred radicals via a single electron transfer (SET) process or energy transfer process under mild reaction conditions, compared to the traditional radical reactions that use high-energy ultraviolet (UV) light or highly toxic and expensive radical initiators [2]. Therefore, visible-lightmediated photo-redox catalysis has been widely applied for the synthesis of natural products, synthetic methodologies, enantioselective catalysis, and polymerization reactions. The success of any photochemical reactions relies on the ability of photocatalysts, usually transition-metal based complexes, organic dyes or heterogeneous semiconductors which promote single-electron transfer (SET) with organic molecules upon excitation with visible light [3]. An alkene difunctionalization can introduce two functional groups in a signal operation across the double bond (**Figure 1**) [4]. In this context, the radical-mediated C-N bond formation has

**Figure 1.** *Difunctionalization of alkene via visible-light photo-redox catalysis.*

emerged as a powerful strategy to construct valuable molecules that have found application in different fields [5]. Therefore, this chapter focuses mainly on the difunctionalization of C=C bonds emphasizing the C-N bond formation using visible-light photo-redox catalysis.
