Alkyl‐C‐C‐Bindungsbildung durch Nickel/Photoredox‐Kreuzkupplung

Abstract

Die Verbindung von Photoredox‐ und Nickel‐Katalyse führte zu einer Renaissance in der Radikalchemie und bei nickelkatalysierten Umsetzungen, insbesondere für die Kohlenstoff‐Kohlenstoff‐Bindungsbildung. Gemeinsam unterstützen diese Entwicklungen die Lösung des seit langem bestehenden Problems der Kreuzkupplung funktionalisierter Alkylfragmente in späten Synthesestadien. Basierend auf der Vorstellung, dass photokatalytisch erzeugte Alkylradikale leicht von Ni‐Komplexen eingefangen werden können, sind gänzlich neue Ausgangsstoffe für die Kreuzkupplung denkbar. In diesem Kurzaufsatz werden die neuesten Entwicklungen für mehrere Arten von Alkyl‐Kreuzkupplungen beleuchtet, die ausschließlich durch diesen Ansatz verwirklicht werden können.

Shining Light on C−S Bonds: Recent Advances in C−C Bond Formation Reactions via C−S Bond Cleavage under Photoredox Catalysis

“…Visible‐light‐induced radical decarboxylative functionalization of carboxylic acids and their derivatives has recently received considerable attention as a novel and efficient method to construct C−C and C‐heteroatom bonds [52] . The radical species formed from the decarboxylation step can participate in not only single photocatalytic transformations, but also dual‐catalytic cross‐coupling reactions by combining photoredox catalysis with other catalytic processes, such as transition metal catalysis [17e,f,53] . However, there are nearly no works using the S ‐based analogues, such as xanthate, for the construction of C−C bond catalyzed by photoredox process via radical pathway.…”

Catalyst‐free Hantzsch Ester‐mediated Organic Transformations Driven by Visible light

“…HE can be readily synthesized from simple starting materials with a considerable structural variation. Despite the three recent elegant reviews by Cheng [2] Molander [3] and Chen [4] covering the use of HEs as an electron donor, proton source, hydrogen atom donor and carbon radical donor in visible‐light photoredox catalysis. Most of these reactions proceeded with either single electron transfer (SET) in the presence of the catalytic amount of metal or organic dye as a photoredox catalyst and a few examples of Energy transfer (ET) pathways through the formation of EDA complexes with suitable substrates.…”

“…Hantzsch ester (HE) is primarily employed as a hydride donor [1] or electron source (E red = + 1.0 V vs. SCE) in its ground state and serve as a potent single-electron reductant (E red* = À 2.28 V vs. SCE) upon photoexcitation (Figure 1). [2][3][4] Hantzsch ester absorbs strongly in the UV region and also it has considerable absorption in the visible-light region tailing to 400-435 nm. HE can be readily synthesized from simple starting materials with a considerable structural variation.…”

Visible‐Light‐Mediated Regioselective Allylation, Benzylation, and Silylation of Methylene‐Malononitriles via Photoredox‐Induced Radical Cation Fragmentation

“…Recently, Melchiorre and co‐workers reported an elegant enantioselective catalytic β‐alkylation of enals with alkyltrimethylsilanes under visible‐light irradiation, presenting a rare method of carbon radical generation from organosilicon compounds under mild visible‐light conditions . Moreover, Molander and co‐workers have developed novel dual nickel/photoredox cross‐couplings by use of a new class of hypercoordinate silicates, which acts as an effective radical precursor under visible‐light photoredox catalysis . Inspired by these pioneering work and also as our continuous studies on visible‐light photocatalysis for activation of inert chemical bonds, we herein report visible‐light‐mediated allylation, benzylation, and silylation of methylene‐malononitriles with allylsilanes, benzylsilanes, and disilanes by utilizing only an organo‐photocatalyst via photoredox‐induced σ‐C–Si + · or σ‐Si–Si + · type radical cation fragmentation.…”