Advancements and Challenges in Reductive Methylation of Carbon Dioxide

Methylation reactions have extraordinary value in organic chemistry, ranging from the assembly of structurally diverse organic functional chemicals to the introduction of methyl groups into pharmaceutical and agrochemical intermediates. In the context of sustainable chemistry, carbon dioxide (CO2) has emerged as an idea and alternative greener C1 source. As a result, reductive methylation strategies utilizing CO2 as a methylating agent have garnered substantial research interest in recent decades, particularly for synthesizing methylated derivatives, compounds with broad applications in drug discovery and agrochemical development. In this review, reductive methylations using CO2 as C1 synthon have been summarized and discussed in detail with focus on metal‐catalyzed C/N‐methylation reactions, base catalyzed C/N‐methylation reactions, ionic liquids catalyzed C/N‐methylation reactions, and catalyst‐free C/N‐methylation reactions based on various reductants. We also elucidate substrate compatibility in these reductive methylations, competing side reactions, and representative reaction mechanisms. Furthermore, conclusions and future trends are depicted finally in this review.