The current report represents a transition‐metal‐free synthesis of oxazoline and isoxazoline derivatives by a tandem electro‐oxidative chalcogenation‐cyclization process. Both C−Se and C−S bond‐forming protocols were developed without using any external oxidant and the reaction was performed at room temperature, open to the air. Using this methodology, 29 substituted oxazoline and 16 substituted isoxazoline derivatives were synthesized with up to 91% isolated yield.
This study reveals a transition-metal-and external oxidant-free electrochemical method for the C3−H sulfonylation of biologically diverse 2H-indazoles at room temperature and under ambient air. Using various sulfonyl hydrazides as the sulfonyl precursor, a series of sulfonylated indazole derivatives containing a broad spectrum of functional groups were synthesized in up to 92% yield. Mechanistic studies suggest a precedented radical pathway is operating in the electrochemical process.
An environmentally benign and proficient electrooxidative tandem azidation-radical cyclization strategy is reported. Manganese-catalyzed electrochemical reaction in an undivided cell at room temperature and the use of NaN 3 as the cheapest azide source are the key features of this protocol. Using this approach, a series of oxindole and quinolinone derivatives are synthesized in high yields. The synthesized azide functionality was efficiently converted to various valuable derivatives.
A one-pot
cascade transformation consisting of an electrochemically
driven azidation of 2H-indazole followed by coarctate
fragmentation is developed to synthesize the 2-azo-benzonitrile motif.
This manganese-catalyzed transformation is external-chemical-oxidant-free
and operates at ambient temperature under air. This methodology exhibits
good functional group tolerance, affording a broad range of substrate
scopes of up to 89% isolated yield. Diverse derivatization of the
2-azo-benzonitrile product resulted in other valuable scaffolds.
In last decade, nickel-catalyzed organic reactions made tremendous progress due to their distinctive redox character. It has unfolded many contemporary synthetic transformations namely cross-coupling, carbon-carbon bond cleavage and directed CÀ H functionalization to achieve the targeted medicinal organic molecules in a straightforward manner. Beyond these well documented approaches, dehydrogenative coupling a challenging bond forming strategy by expelling hydrogen from unfunctionalized coupling partners is less explored. In accord with this, nickel-catalyst has been studied to perform different class of dehydrogenative coupling between easily accessible substrates. Nickel catalyzed processes for the construction of carbon-carbon, carbon-heteroatom and heteroatom-heteroatom bonds by dehydrogenation are discussed herein in a sustainable manner.[a] Dr.
Electrochemical organic transformations have made enormous progress over the past decades owing to the idiosyncratic redox nature. Electrochemistry is globally acknowledged for its sustainability and environ friendliness and several well-known redox processes get a new exquisite touch without expelling chemical waste and toxic by-products. Apart from this, electrochemistry has adequate potential to steer numerous non-spontaneous reactions like cross-coupling, C−C bond cleavage, radical generation, directed C–H functionalization reactions etc. in a straightforward manner. Beyond the electrochemical oxidation reactions, electrochemical reductive transformations are also enriching in the last few years. Electrochemical reduction can be facilitated by using different strategies like using a sacrificial electrode, sacrificial reagent or can be accomplished in a divided cell. In this short review, different methods for the functionalization of C−halogen bonds, including detailed mechanistic approaches, are discussed.
1 Introduction
2 Different strategies for the electrochemical reduction
3 Functionalization of C−halogen bonds through electrochemical reduction
3.1 Electro-reductive hydrodehalogenation
3.2 Electro-reductive C−C coupling of organohalides
3.2.1 Aryl-aryl C−C coupling
3.2.2 Aryl-alkenyl C−C coupling
3.2.3 Aryl-alkyl C−C coupling
3.2.4 Alkyl-alkenyl C−C coupling
3.2.5 Alkyl-alkyl C−C coupling
3.3 Electro-reductive coupling of organohalides with carbonyls (C=O)
3.4 Electro-reductive coupling of organohalides with organoborones
4 Conclusion
The current methodology reveals a green and proficient electro-oxidative tandem selenocyclization of thioallyl benzoimidazoles manufacturing selenylated dihydro-benzoimidazo-thiazine derivatives. Both CÀ Se and CÀ N bond formation were achieved via this mild protocol which exhibits good functional group tolerability affording an extensive range of substrate scope up to 96% isolated yields. Complete control over the regioselective formation of the six-membered heterocycle and stereoselective construction of the contiguous stereocenters was established. The practical electrochemical method operates in an undivided cell at ambient temperature without using any metal and external chemical oxidant.
A positively charged micelle, loaded with substrates was transported selectively to the reaction site (cathode) to promote the proximity and localization of the reactants (ester and hydroxide). The guided vehicular...
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