Light and cobalt cooperation: radical-driven remote migration of carbon–carbon double bonds and functional groups!

Under the cobalt-catalyzed system, the EPR signal intensity is higher than that under the pure photocatalytic system, indicating that cobalt species likely play a synergistic role in stabilizing or promoting radical generation. This observation rules out ionic pathways and provides experimental evidence for elucidating the selectivity mechanism of the cobalt catalyst in remote C(sp³)–H dehydrogenation. Energy Profile and Synergistic Mechanism The EPR experiment confirms the presence of radicals; to understand how they drive double-bond migration and remote dehydrogenation, an energy-based analysis of the cobalt catalyst’s synergistic effect is required. The free-energy profile constructed via DFT calculations reveals the thermodynamic driving force and kinetic selectivity of the reaction. Figure 3: DFT calculations reveal the reaction’s free-energy profile—overall exothermic from substrate to product, with a key transition state barrier of only 13.8 kcal/mol, supporting a thermodynamically favorable migration mechanism. Calculations show that the overall transformation from substrate to product is significantly exothermic. The activation barrier of the key transition state TS-1 is merely 13.8 kcal/mol, indicating that the hydrogen-atom transfer (HAT) step can proceed efficiently under mild conditions. This low-barrier characteristic is directly attributable to cobalt-catalyzed activation of the HAT process, effectively lowering the reaction’s activation energy. Intermediates R₁ and R₃ along the pathway reside in deep energy wells at −15.7 kcal/mol and −24.3 kcal/mol, respectively, confirming their stability as reaction intermediates. Such stability affords a sufficiently long time window for radical-initiated C=C double-bond migration, thereby suppressing side reactions. The final product 11 lies at −21.4 kcal/mol—far lower in energy than the starting material. This thermodynamic advantage not only drives the reaction forward but also explains why the reaction preferentially yields a specific isomeric product. The mutual corroboration between theory and experiment fully maps out the microscopic picture of radical initiation and selective control within the light/cobalt dual catalytic cycle. Background and Challenges Multisite functionalization of molecules is a crucial strategy for synthesizing complex compounds; however, simultaneously modifying both reactive sites and inert remote C(sp³)–H bonds remains highly challenging. Conventional methods such as olefin metathesis or shuttle catalysis can achieve migration of double bonds or functional groups, yet they cannot concurrently activate remote C–H bonds and reconstruct C=C bonds. This limitation arises primarily because remote C–H bonds possess high bond dissociation energies and exhibit poor site-selectivity, leading to frequent competing reactions and restricting the applicability of these approaches. To address this challenge, we propose a novel radical-triggered migration strategy. Using a dual catalytic system combining light and cobalt, we initiate intramolecular migration via radical addition, followed by C=C bond reconstruction. This approach avoids direct cleavage of high-energy C–H bonds and instead achieves remote dehydrogenation through cobalt-promoted, selective hydrogen-atom transfer. Not only does this strategy overcome the longstanding difficulty of simultaneously accomplishing double-bond reconstruction and remote C–H activation, but it also opens new avenues for precise modification of complex molecules. Summary and Outlook Our strategy breaks traditional limitations by achieving remote migration of functional groups from the 1,2- to the 1,6-position, with both site selectivity and E/Z selectivity exceeding 20:1.

Why are these two organic compounds named 'pentadiene' and 'xylene', respectively—and why does the numeral 'di-' occupy different positions in the two names?

'Di-' directly modifies the term immediately following it: 'diene' means two double bonds, whereas 'dimethyl' means two methyl groups.

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