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Palladium catalysis induced by visible light is an emerging field of catalysis. In contrast to classical reactions catalyzed by Pd complexes in the ground state, which mostly proceed through two‐electron redox processes, the mechanisms of these new methods based on photoexcited Pd complexes usually operate through transfer of a single electron. Such processes lead to putative hybrid Pd/radical species, which exhibit both radical and classical Pd‐type reactivity. This Minireview highlights the recent progress in this rapidly growing area.

 

A novel mild, visible‐light‐induced palladium‐catalyzed hydrogen atom translocation/atom‐transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5‐HAT process of previously unknown hybrid vinyl palladium radical intermediates, thus leading to iodomethyl carbo‐ and heterocyclic structures.

 

The Mizoroki–Heck reaction is one of the most efficient methods for alkenylation of aryl, vinyl, and alkyl halides. Given its innate nature, this protocol requires the employment of compounds possessing a halogen atom at the site of functionalization. However, the accessibility of organic molecules possessing a halogen atom at a particular site in aliphatic systems is extremely limited. Thus, a protocol that allows a Heck reaction to occur at a specific nonfunctionalized C(sp³)−H site is desirable. Reported here is a radical relay Heck reaction which allows selective remote alkenylation of aliphatic alcohols at unactivated β‐, γ‐, and δ‐C(sp³)−H sites. The use of an easily installed/removed Si‐based auxiliary enables selective I‐atom/radical translocation events at remote C−H sites followed by the Heck reaction. Notably, the reaction proceeds smoothly under mild visible‐light‐mediated conditions at room temperature, producing highly modifiable and valuable alkenol products from readily available alcohols feedstocks.

 

The first visible light‐induced Pd‐catalyzed Heck reaction of α‐heteroatom substituted alkyl iodides and ‐bromides with vinyl arenes/heteroarenes has been developed. This transformation efficiently proceeds at room temperature and enables synthesis of valuable functionalized allylic systems, such as allylic silanes, boronates, germanes, stannanes, pivalates, phosphonates, phthalimides, and tosylates from the corresponding α‐substituted methyl iodides. Notably, synthesis of the latter substrates failed under existing thermally induced Pd‐catalyzed conditions, which highlights the importance of visible light for this transformation.

 

The Heck reaction is one of the most reliable and useful strategies for the construction of C–C bonds in organic synthesis. However, in contrast to the well-established aryl Heck reaction, the analogous reaction employing alkyl electrophiles is much less developed. Significant progress in this area was recently achieved by merging radical-mediated and transition-metal-catalyzed approaches. This review summarizes the advances in alkyl Heck-type reactions from its discovery early in the 1970s up until the end of 2018. 1 Introduction 2 Pd-Catalyzed Heck-Type Reactions 2.1 Benzylic Electrophiles 2.2 α-Carbonyl Alkyl Halides 2.3 Fluoroalkyl Halides 2.4 α-Functionalized Alkyl Halides 2.5 Unactivated Alkyl Electrophiles 3 Ni-Catalyzed Heck-Type Reactions 3.1 Benzylic Electrophiles 3.2 α-Carbonyl Alkyl Halides 3.3 Unactivated Alkyl Halides 4 Co-Catalyzed Heck-Type Reactions 5 Cu-Catalyzed Heck-Type Reactions 6 Other Metals in Heck-Type Reactions 7 Conclusion 

A highly efficient and practical method for incorporation of arylmethylpyridyl moiety into diverse molecules has been developed. This method features the transition metal-free light-induced room temperature transformation of pyridotriazoles into pyridyl carbenes, which are capable of smooth arylation, X–H insertion, and cyclopropanation reactions. The synthetic usefulness of the developed method was illustrated in a facile synthesis of biologically active molecules. 

A new mode of S–O bond activation has been discovered, which constitutes novel reactivity of easily available and bench-stable arylsulfonate phenol esters. This protocol enables access to putative sulfonyl radical intermediates, which enable straightforward access to valuable vinyl sulfones.