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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 

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.

 

Durch sichtbares Licht induzierte Palladiumkatalyse ist ein aufstrebendes Teilgebiet der Katalyse. Im Unterschied zu klassischen, durch Pd‐Komplexe im Grundzustand katalysierten Reaktionen, die vornehmlich durch Zweielektronen‐Redoxprozesse voranschreiten, laufen die Mechanismen der neuartigen Reaktionen auf Basis photoangeregter Pd‐Komplexe meist durch die Übertragung eines einzelnen Elektrons ab. Diese Prozesse führen mutmaßlich zu hybriden Pd/Radikal‐Spezies, die sowohl die Reaktivität von Radikalen als auch die von klassischen Pd‐Spezies aufweisen. Dieser Kurzaufsatz beleuchtet aktuelle Fortschritte auf diesem schnell wachsenden Gebiet.

 

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 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.