Next, we sought to utilize the forward reaction and reversible halogenation for a halogen sorting reaction. In the original manufacturing process of Valsartan reported by Novartis, the C-H bromination of 1v was performed with NBS and AIBN in chlorobenzene at 100 °C. To prevent excessive product loss through overhalogenation, the reaction was carefully monitored and stopped at 70% conversion, the chlorobenzene evaporated, and the overhalogenated 2v' was removed by solvent washes, followed by addition of more NBS and resubjecting the remaining starting material. Using our method, we stopped the reaction at ~80% conversion, then resubjecting the mixture (0.42 mmol of 2v, 0.075 mmol of 2v', 0.125 mmol of 1v) to the catalytic Figure . Figure . A. Increasing the yield of the first step in synthesis of Valsartan by halogen sorting of the mixture of brominated products, and directly by catalytic C-H bromination. B. [2+2] cycloaddition of in situ generated dichloroketene with indene to afford 3ad followed by selective monodechlorination. chlorinating conditions. 2v' could be reconverted to the desired 2v, boosting the total amount of 2v to 0.48 mmol. As an alternative to the halogen sorting process, 1v can also directly be brominated to exclusively form 2v in 71% yield using our standard catalytic brominating conditions. In addition to halogen sorting from overhalogenation, we envisioned synthetic contexts where the overall reversibility of our process could be used for selective monodehalogenation. Using the product of a [2+2] dichloroketene-alkene cycloaddition 3w', we observed selective monodechlorination of 3w' to 3w as a single diastereomer in high yield. The high chemoselectivity of Cu-1 for the most electron poor halide, and the formation of benzyl chloride (3a) likely prevent complete dechlorination and allow controlled monodechlorination. Indeed, attempts to form the same versatile synthetic intermediate 3w using classical Zn/H+ conditions only provided mixtures of 3w, 3w', and 1w (See SI for full experimental details).