This book is a comprehensive study exploring the innovative use of Deep Eutectic solvents (DES) for synthesizing Pyrimidine derivatives. Authored by a team of chemists, the book delves into environmentally friendly and efficient methodologies for organic synthesis. The DES in focus, composed of choline chloride and tartaric acid, serves as a sustainable alternative to traditional solvents, offering significant advantages in terms of biodegradability, low toxicity, and ease of preparation. The book begins with an overview of Pyrimidine derivatives, highlighting their importance in pharmaceuticals, agrochemicals, and materials science due to their diverse biological and chemical properties. The authors discuss the reaction mechanisms, showcasing how the DES facilitates proton transfers and stabilizes transition states. Throughout, the book underscores the green chemistry principles,emphasizing reduced environmental impact and improved safety profiles. Concluding remarks highlight future directions, suggesting broader applications of DES in various chemical synthesis and industrial processes. This work serves as a valuable resource for researchers and practitioners in green chemistry.