New Redox Strategies in Organic Synthesis by Means of Electrochemistry and Photochemistry

Abstract

As the breadth of radical chemistry grows, new means to promote and regulate single-electron redox activities play increasingly important roles in driving modern synthetic innovation. In this regard, photochemistry and electrochemistry—both considered as niche fields for decades—have seen an explosive renewal of interest in recent years and gradually have become a cornerstone of organic chemistry. In this Outlook article, we examine the current state-of-the-art in the areas of electrochemistry and photochemistry, as well as the nascent area of electrophotochemistry. These techniques employ external stimuli to activate organic molecules and imbue privileged control of reaction progress and selectivity that is challenging to traditional chemical methods. Thus, they provide alternative entries to known and new reactive intermediates and enable distinct synthetic strategies that were previously unimaginable. Of the many hallmarks, electro- and photochemistry are often classified as “green” technologies, promoting organic reactions under mild conditions without the necessity for potent and wasteful oxidants and reductants. This Outlook reviews the most recent growth of these fields with special emphasis on conceptual advances that have given rise to enhanced accessibility to the tools of the modern chemical trade.

Synthesis of Acridinium Photocatalysts via Site-Selective C–H Alkylation

“…This method demonstrated excellent compatibility with primary (3-10), secondary (11)(12)(13)(14)(15)(16)(17)(18), and tertiary (19)(20)(21)(22) alkylorganotrifluoroborates, providing easy access to acridinium dyes with different steric properties. A highly useful feature of our method is that the monoalkylated product can be alkylated again following the above experimental procedures to furnish novel, 3,6-dialkylated acridinium dyes, using the same (28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45) The alkylation reaction could be scaled up to decagram without difficulty by employing a continuous-flow photochemical reactor 45,46 and a electrochemical batch reactor, as demonstrated in the synthesis of 10.88 g of 36 in 80% yield (Fig. 4A).…”

“…Photochemically induced single-electron transfer between acridiniums and organotrifluoroborates is known to generate a persistent acridine radical and a transient alkyl radical 22,23 , which we hypothesize could couple to form a C-C bond in the absence of radical acceptors. Herein we report the synthesis of acridinium photocatalysts via siteselective late-stage C−H alkylation using organotrifluoroborates through sequential photochemical addition and electrocatalytic [24][25][26][27][28][29][30][31][32][33][34][35][36] dehydrogenation (Fig. 1C).…”

Unlocking the Potential of High-Throughput Experimentation for Electrochemistry with a Standardized Microscale Reactor

“…Over the past decade, synthetic electrochemistry has garnered significant interest in the organic chemistry community. [1][2][3][4][5][6] In an electrochemical reaction, electrons flowing between an anode and a cathode provide the redox equivalents to drive chemical transformations in lieu of traditional chemical oxidants or reductants. Under a sufficient current or potential, substrates can be oxidized or reduced at the electrode to generate reactive intermediates such as radicals and radical ions.…”

Photocatalyzed Chemo‐Selective Alkylation of Quinones and Phenothiazinones with Alkyl Amides: Photophysical and Cytotoxic Activity Studies

“…Application of photochemical techniques in organic synthesis paved way for access to new and novel reactive intermediates, which can be used in potential new bond disconnection strategies, enables reaction discoveries and gain precise control over the reaction progress that are inaccessible or impracticable through alternative methods [14f] . Further, photochemical reactions proceed under mild conditions and often with reduced environmental impact.…”