The atroposelectivity of Larock cyclization is explained as follows: Initially, Pd(0) undergoes oxidative addition to the Ar-Br of the Larock Cyclization precursor 25. Subsequently, Pd(II) undergoes migratory insertion into the internal akyne, leading to the formation of a six-membered palladacycle 27 or 30. At this stage, the desired transition state 29, which gives the desired atropisomer, is 55.2 kJ/mol more stable compared to the undesired transition state 26 (see supporting information for more details about the DFT calculation). Therefore, the reaction predominantly proceeds from transition state 29, resulting in the atroposelective formation of the desired cyclized compound 31 as a single entity. To assess the thermal stability of the atrop-Tyr-Trp linkage formed by Larock cyclization, compound 31 was heated in toluene at 120 °C, confirming the absence of isomerization. Undesired atropisomer 28 was not observed at all. From these experimental results, it became evident that the atrop-Tyr-Trp linkage in compound 31 is thermodynamically stable in its preferred conformation.