A carbene insertion into electron‐deficient C−H bonds of 1,3‐diesters, β‐ketoesters, β‐ketonitriles, and malononitriles was realized by using CuCN/PCy3 as the catalyst. The reaction provides a straightforward approach to the synthetically important multi‐substituted succinic acid derivatives. A plausible reaction mechanism with cyclopropanation/ring opening as key steps was proposed based on control experiments. Copper catalysis: A formal carbene insertion into electron‐deficient C−H bonds of 1,3‐diesters, β‐ketoesters, β‐ketonitriles, and malononitriles was realized by using CuCN/PCy3 as the catalyst. The reaction provides a straightforward approach to the multi‐substituted succinic acid derivatives. The mechanistic studies suggested that this formal C−H bond insertion reaction likely proceeds through a cyclopropanation of enol and a ring‐opening reaction sequence.