Palladium-Catalyzed Radical Reactions via Pd(I) Pathway: A Brief Summary of Reaction Patterns and Recent Progress

doi:10.6023/cjoc202512048

Abstract

In the toolbox of modern organic synthesis, palladium-catalyzed reactions represent a vital category that has long been considered to follow classical two-electron pathways. However, research over the past two decades, and particularly recent breakthroughs, has demonstrated the existence of a parallel and equally significant field: palladium-catalyzed reactions involving single-electron transfer (SET), halogen atom transfer (XAT), and radical mechanisms. This new reaction paradigm not only expands the catalytic capability of palladium, enabling the activation of traditionally inert chemical bonds, but also offers the potential to achieve novel chemoselectivity, regioselectivity, and stereoselectivity. This review aims to organize this frontier field, focusing primarily on radical pathways that proceed via Pd(I) intermediates. In these reactions, palladium primarily acts as a radical initiator, generating radicals through redox processes of ground-state or excited-state Pd(0), or via the homolysis of Pd(II)—C bonds. The typical palladium oxidation state cycle is Pd(0)-Pd(I)-Pd(II). From the perspective of radical generation methods, this review categorizes radical reaction patterns involving Pd(I) intermediates, summarizes recent progress in the field, and provides commentary on the underlying reaction mechanisms.

Key words: palladium catalysis, radical chemistry, organometallic chemistry

Cite this article

Yi-Fan Tan, Lei Jiao. Palladium-Catalyzed Radical Reactions via Pd(I) Pathway: A Brief Summary of Reaction Patterns and Recent Progress[J]. Chinese Journal of Organic Chemistry, 2026, 46(4): 1303-1319.

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Fig. & Tab. 39

Scheme 1. Typical two-electron and single-electron processes in palladium catalysis

Scheme 2. Two modes of generating Pd(I) and free radicals

Scheme 3. Benzoazepine synthesis by radical cascade cyclization reaction

Scheme 4. Photopromoted intramolecular Heck reaction

Scheme 5. Heck reaction of pre-activated alcohol

Scheme 6. PAHs synthesis enabled by radical cyclization

Scheme 7. Divergent synthesis of aza-[2.1.1] and [4.1.1]bicycles

Scheme 8. Boron-iodide swap reaction

Scheme 9. 1,4-Aminoarylation of 1,3-butadienes

Scheme 10. Asymmetric cascade dearomatization of indoles

Scheme 11. Hydroxyl directed 1,2-aminoalkylation of aromatic alkenes

Scheme 12. Access to vinyl gem-difluorinated cyclopropanes via photopromoted Heck reaction

Scheme 13. Access to C2-allyl carbohydrates via radical allylic alkylation

Scheme 14. Convergent approach to functionalized allylic compounds

Scheme 15. Enantioselective cascade carboamidation of dienes to access γ-lactams

Scheme 16. 1,4-Dicarbofunctionalization of 1,3-butadiene

Scheme 17. Enantioselective three-component allylic alkylation of α-amino esters

Scheme 18. 1,4-Bifunctionalization of dienes by alkyl chloride

Scheme 19. Radical Heck reaction of alkyl chloride

Scheme 20. Synthesis of isoquinuclidines via selective dechlorination

Scheme 21. Defluorinative Suzuki coupling of trifluorome- thylarenes

Scheme 22. 1,4-Difunctionalization of dienes by trifluoromethylarenes

Scheme 23. Defluorinative multicomponent cascade reaction of trifluoromethylarenes

Scheme 24. Radical Heck coupling of isonitriles and vinyl arenes

Scheme 25. Scope of electrophiles that can interact with photoexcited Pd(0)

Scheme 26. 1,4-Dicarbofunctionalization of 1,3-dienes mediated by C—H activation

Scheme 27. Hydrogen-iodide swap reaction

Scheme 28. Stereodivergent synthesis of functionalized allylic compounds

Scheme 29. Formal [2＋2] cycloaddition of alkylarenes and imines

Scheme 30. Allylic C—H alkylation of alkenes

Scheme 31. α-Alkenylation of amines through radical Heck reaction

Scheme 32. Formation of aryl ketyl radicals and its reaction

Scheme 33. Formation of alkyl ketyl radicals and its reaction

Scheme 34. Photopromoted palladium-catalyzed acylation of halides

Scheme 35. Three modes of interaction between Pd(0) and substates

Scheme 36. Evidence for XAT between Pd(0) and the substrate

Scheme 37. Photopromoted homolysis of Pd(II)—R bond

Scheme 38. Synthesis of tBu-Xantphos-Pd(I) complex and evidence for related reactions

Scheme 39. Synthesis of dtbpf-Pd(I) complex and evidence for related reactions

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