Shuttle Catalysis—New Strategies in Organic Synthesis

Abstract

Shuttle catalysis has recently emerged as a powerful new concept that provides a platform for performing both functionalization and defunctionalization reactions. In this concept article, applications of shuttle catalysis as a novel strategy in organic synthesis are discussed. This includes using forward shuttle catalysis reactions for challenging bond-forming processes that avoid the use of hazardous chemicals. Shuttle catalysis also facilitates the transfer of reactive functionality as a route to procure a broad range of compounds using one simple procedure. Reverse shuttle catalysis reactions are also discussed as a method for the valorization of biomass and waste materials. Another area of interest, shuttle-catalysis-assisted reactions, wherein the transfer of a small molecule is utilized in a catalytic cycle, is also described. Possible future directions in this exciting new field are also suggested.

Iridium‐Catalyzed Hydrochlorination and Hydrobromination of Alkynes by Shuttle Catalysis

“…We initially explored reagents that are similar in structure to those previously employed in other examples of shuttle catalysis by reaction with asimple aliphatic terminal alkyne (1;s ee Table 1). [15] We started our investigations with iridium catalysts because of their expected high reactivity toward the oxidative addition of CÀXbonds. [16] Unfortunately,b oth isobutyl chloride (entry 1) and butyl chloride (entry 2) did not show any reactivity,p robably because of the inertness of the C À Cl bond.…”

“…Research Articles alkynes.Abroad range of functional groups,including nitriles (8), chlorides (9), esters (10), amines (12), nitro (16), aryl chloride (17), aryl fluorides (18), iodide (19), aldehyde (22), and ketone (29)w ere tolerated. Likewise, a,b-unsaturated esters,which serve as an important building block in organic synthesis,w ere tolerated under the reaction conditions (15). Interestingly,asubstrate bearing two terminal alkyne moieties could undergo successful hydrochlorination reaction giving the product containing two vinyl chloride moieties (7).…”

Iridium‐katalysierte Hydrochlorierung und Hydrobromierung von Alkinen durch Shuttlekatalyse

“…Beispiele dazu sind die HCN-freie Hydrocyanierung, [12] die Cyanid-freie Cyanierung von Säurechloriden [13] und die CO/HCl-freie Hydrochlorcarbonylierung. [14] Diese Reaktionen verlaufen nach dem Prinzip der Shuttlekatalyse, [15] bei dem eine chemische Einheit zwischen zwei stabilen organischen Molekülen übertragen wird. Dementsprechend suchten wir nach einem geeigneten katalytischen System, mit dem ein HCl-Molekülformal zwischen einem einfachen Alkylchlorid und einem Alkin ohne direkten Einsatz von korrosivem HCl übertragen werden kann.…”

“…Zunächst untersuchten wir Reagenzien mit ähnlicher Struktur wie in früheren Beispielen der Shuttlekatalyse,die mit einem einfachen aliphatischen terminalen Alkin 1 reagieren. [15] Wir begannen unsere Untersuchungen mit Iridiumkatalysatoren wegen ihrer erwartet hohen Reaktivitätg egenüber der oxidativen Addition von C-X-Bindungen. [16] Leider zeigten sowohl Isobutylchlorid ( [a] 1 (0.1 mmol), 2 (0.2 mmol), [IrCl(cod)] 2 (2.5 mol %), CPhos (8), Chloride (9), Ester (10), Amine (12), Nitro (16), Arylchloride (17), Arylfluoride (18), Aryliodide (19), Aldehyde (22)u nd Ketone (29)w urden toleriert.…”

Nickel‐Catalyzed Cyanation of Aryl Chlorides and Triflates Using Butyronitrile: Merging Retro‐hydrocyanation with Cross‐Coupling

“…Thei nstallation of ac yano group through transitionmetal-catalyzed activation of C À CN bonds enables the use of inexpensive and less toxic alkyl nitriles as reagents. [12] This strategy provides acontrolled way to generate metal cyanide intermediates without employing metal cyanide sources, thereby avoiding both catalyst deactivation and exposure to toxic reagents.R ecently,o ur group reported ar eversible nickel-catalyzed transfer hydrocyanation through shuttle catalysis [13] that employed as imple alkyl nitrile as an HCN donor to convert alkenes into nitriles. [14] Inspired by the transfer mechanism of the hydrocyanation process,wehypothesized that simple alkyl nitriles bearing bhydrogens could possibly be employed as cyanating reagents in the transition-metal-catalyzed cyanation of aryl (pseudo)halides (Scheme 1b).…”