Photochemical Asymmetric Nickel‐Catalyzed Acyl Cross‐Coupling

Abstract

Photochemical enantioselective nickel‐catalyzed cross‐coupling reactions are difficult to implement. We report a visible‐light‐mediated strategy that successfully couples symmetrical anhydrides and 4‐alkyl dihydropyridines (DHPs) to afford enantioenriched α‐substituted ketones under mild conditions. The chemistry does not require exogenous photocatalysts. It is triggered by the direct excitation of DHPs, which act as a radical source and as a reductant, facilitating the turnover of the chiral catalytic nickel complex.

Air‐Stable Fe3O4@SiO2‐EDTA‐Ni(0) as an Efficient Recyclable Magnetic Nanocatalyst for Effective Suzuki‐Miyaura and Heck Cross‐Coupling via Aryl Sulfamates and Carbamates

“…As a result of these studies, aryl carbamates and sulfamates were considered ideal precursors because of their extensive derivatives, availability, high stability and more efficiency under a variety of reaction conditions. [15] Despite these significant advances that happened in recent years, [16][17][18][19] however, this reaction suffers from several limitations including high catalyst loading, long reaction times, elevated temperature regime and the necessity to employ additional quantities of the phosphine ligands. [17] It should be noted that the use of large quantities of ligands and metals as catalytic systems create a remarkable complexity in the purification, increase waste materials, decrease the safety of reaction and low to modest yields have resulted in the most cases.…”

Stereoinduction in Metallaphotoredox Catalysis

“…[19] Direct excitation of redox-active radical precursors,without the necessity for an exogenous photocatalyst, offers new avenues in Ni-catalyzed asymmetric transformations.M elchiorre et al validated the use of 1,4-dihydropyridines (1,4-DHPs) as potent photoreductants to achieve this goal (Scheme 8). [20] Upon excitation at 405 nm, the corresponding alkyl DHP (E 1/2 = À1.6 Vv s. Ag/Ag + in MeCN) participates in two sequential SET events with aN i II precatalyst to generate the desired active Ni 0 species and ar adical cation. Thel atter undergoes ah omolytic fragmentation to deliver asecondary alkyl radical.…”

Stereoinduktion in der Metallaphotoredoxkatalyse

“…So setzten Melchiorre et al 1,4-Dihydropyridine (1,4-DHPs) als potente Photoreduktanten ein (Schema 8). [20] Nach Anregung bei einer Wellenlänge von 405 nm geht das Alkyl-DHP (E 1/2 = À1.6 Vg egen Ag/Ag + in MeCN) zwei SET-Ereignisse mit dem Ni II -Präkatalysator ein, was zur Bildung der aktiven Ni 0 -Spezies führt. Die homolytische Fragmentierung des hierbei ebenfalls generierten DHP-Radikalkations führt zur Freisetzung sekundärer Alkylradikale.O xidative Addition des symmetrischen Anhydrids sowie nachfolgende radikalische Addition an Ni II führen zum AcylNi III -Komplex.…”