Radicals in Transition Metal Catalyzed Reactions? Transition Metal Catalyzed Radical Reactions? A Fruitful Interplay Anyway

Abstract

This review summarizes the current status of radical-based transition metal catalyzed reactions in organic chemistry. The underlying features of radical generation from transition metal complexes and radical reactivity in the framework of transition metal catalysis are discussed. The available arsenal to detect radicals in transition metal catalyzed transformations is presented. Available strategies to combine radical intermediates with transition metal catalysis are outlined. In the main part the currently known synthetic methodology of transition metal catalyzed reactions proceeding via radical intermediates is discussed. This part covers catalytic radical reactions involving group 4 to group 7 elements.

Transition-Metal Catalysis of Nucleophilic Substitution Reactions: A Radical Alternative to SN1 and SN2 Processes

“… 8 This then opens the door to metal-catalyzed substitutions of alkyl halides through catalytic cycles analogous to those previously reported for aryl halides (e.g., Figure 6 ). 9 …”

Nickel-Catalyzed Regiodivergent Opening of Epoxides with Aryl Halides: Co-Catalysis Controls Regioselectivity

“…The results demonstrate the potential of new cross-coupling reactions based upon the interplay of radicals and transition-metal catalysis. 27 Further improvement of the selectivities, including the development of enantio-selective variants 12f–g and longer-lived titanium catalysts, is currently underway and will be reported in due course.…”

Copper-Catalyzed Synthesis of Hindered Ethers from α-Bromo Carbonyl Compounds

“…16 Although it is possible that the oxidative addition step involves a radical species (i.e. radical oxidative insertion), 17 it is unlikely that a free radical exists in a significant concentration, given that isobutylene failed to trap the hypothetical radical intermediate. It is noted that in one of their latest reports, the Nishikata group also proposed an oxidative addition/reductive elimination mechanism, although it did not take into consideration the participation of the imino-carboxylate.…”