Reductive carboxylation of organo (pseudo)halides with CO2 is a powerful method to provide carboxylic acids quickly. Notably, the catalytic reductive carbo‐carboxylation of unsaturated hydrocarbons ...via CO2 fixation is a highly challenging but desirable approach for structurally diverse carboxylic acids. There are only a few reports and no examples of alkenes via transition metal catalysis. We report the first asymmetric reductive carbo‐carboxylation of alkenes with CO2 via nickel catalysis. A variety of aryl (pseudo)halides, such as aryl bromides, aryl triflates and inert aryl chlorides of particular note, undergo the reaction smoothly to give important oxindole‐3‐acetic acid derivatives bearing a C3‐quaternary stereocenter. This transformation features mild reaction conditions, wide substrate scope, facile scalability, good to excellent chemo‐, regio‐ and enantioselectivities. The method highlights the formal synthesis of (−)‐Esermethole, (−)‐Physostigmine and (−)‐Physovenine, and the total synthesis of (−)‐Debromoflustramide B, (−)‐Debromoflustramine B and (+)‐Coixspirolactam A; thereby, opening an avenue for the total synthesis of chiral natural products with CO2.
A strategy is presented for nickel‐ catalyzed asymmetric reductive carbo‐carboxylation of alkenes with CO2. A variety of aryl (pseudo)halides react to produce oxindole‐3‐acetic acid derivatives bearing a C3‐quaternary stereocenter. Notably, synthesis of a range of bioactive pyrroloindolines was achieved.
Abstract
Catalytic reductive coupling of two electrophiles and one unsaturated bond represents an economic and efficient way to construct complex skeletons, which is dominated by transition-metal ...catalysis via two electron transfer. Herein, we report a strategy of visible-light photoredox-catalyzed successive single electron transfer, realizing dearomative arylcarboxylation of indoles with CO
2
. This strategy avoids common side reactions in transition-metal catalysis, including ipso-carboxylation of aryl halides and β-hydride elimination. This visible-light photoredox catalysis shows high chemoselectivity, low loading of photocatalyst, mild reaction conditions (room temperature, 1 atm) and good functional group tolerance, providing great potential for the synthesis of valuable but difficultly accessible indoline-3-carboxylic acids. Mechanistic studies indicate that the benzylic radicals and anions might be generated as the key intermediates, thus providing a direction for reductive couplings with other electrophiles, including D
2
O and aldehyde.
The direct functionalization of C-H bonds has drawn the attention of chemists for almost a century. C-H activation has mainly been achieved through four metal-mediated pathways: oxidative addition, ...electrophilic substitution, σ-bond metathesis and metal-associated carbene/nitrene/oxo insertion. However, the identification of methods that do not require transition-metal catalysts is important because methods involving such catalysts are often expensive. Another advantage would be that the requirement to remove metallic impurities from products could be avoided, an important issue in the synthesis of pharmaceutical compounds. Here, we describe the identification of a cross-coupling between aryl iodides/bromides and the C-H bonds of arenes that is mediated solely by the presence of 1,10-phenanthroline as catalyst in the presence of KOt-Bu as a base. This apparently transition-metal-free process provides a new strategy with which to achieve direct C-H functionalization.
Enol and phenol functionalities are very common in organic molecules. Utilization of these materials is very appealing in organic synthesis because they are important alternatives to organohalides in ...cross‐coupling reactions. In this review, we summarize the transition‐metal‐catalyzed cross‐coupling of enol‐ and phenol‐based electrophiles, including phosphates, sulfonates, ethers, carboxylates, and phenolates.
Coupled up! Protected enol and phenol compounds are important alternatives to organohalides in cross‐coupling reactions. The transition‐metal‐catalyzed cross‐coupling of enol‐ and phenol‐based electrophiles, including phosphates, sulfonates, ethers, carboxylates, and phenolates, have been summarized (see scheme; PG=protecting group).
The first thiocarboxylation of styrenes and acrylates with CO2 was realized by using visible light as a driving force and catalytic iron salts as promoters. A variety of important β‐thioacids were ...obtained in high yields. This multicomponent reaction proceeds in an atom‐ and redox‐economical manner with broad substrate scope under mild reaction conditions. Notably, high regio‐, chemo‐, and diasteroselectivity are observed. Mechanistic studies indicate that a radical pathway can account for the unusual regioselectivity.
One flew over the COO→ ‐COOH's nest: The first thiocarboxylation of styrenes and acrylates with CO2 to generate important β‐thioacids was realized by using visible light as a driving force and catalytic iron salts as promoters. This multicomponent reaction features broad substrate scope, mild reaction conditions, and high regio‐, chemo‐, and diasteroselectivity. Mechanistic studies indicate that a radical pathway can account for the unusual regioselectivity.
Over the past decades, organometallic complexes with precious elements, such as ruthenium and iridium, are widely used as visible‐light photoredox catalysts. Recently, more and more complexes based ...on earth‐abundant and inexpensive elements have been used as sensitizers in photochemistry. Although the photoexcited state lifetimes of iron complexes are typically shorter than those of traditional photosensitizers, the utilization of iron catalysts in photochemistry has sprung up owing to their abundance, low price, nontoxicity, and novel properties, including exhibiting ligand to metal charge transfer states. This concept focuses on recent advances in light‐driven iron catalysis in organic transformations, including iron/photoredox dual catalysis, light‐induced iron photoredox catalysis and light‐induced generation of active iron catalysts. The prospect for the future of this field is also discussed.
Light runs across iron catalysts: This Concept summarizes the recent advances in iron/photoredox dual catalysis, photoactive iron catalysts in photochemistry, as well as light‐induced generation of active iron catalysts in organic transformations. Prospects for the future of the field are also discussed.
3DendrAl(l)ene! A new synthesis of 3dendralenes is based on a RhIII‐catalyzed alkenyl CH activation and coupling reaction with allenyl carbinol carbonates (see scheme; DG=directing group). A variety ...of 3dendralenes with diverse substitution patterns are accessible with good efficiency. The reaction is highly stereoselective and compatible with different directing groups and numerous functional groups.
Abstract
Photoredox-mediated umpolung strategy provides an alternative pattern for functionalization of carbonyl compounds. However, general approaches towards carboxylation of carbonyl compounds ...with CO
2
remain scarce. Herein, we report a strategy for visible-light photoredox-catalyzed umpolung carboxylation of diverse carbonyl compounds with CO
2
by using Lewis acidic chlorosilanes as activating/protecting groups. This strategy is general and practical to generate valuable α-hydroxycarboxylic acids. It works well for challenging alkyl aryl ketones and aryl aldehydes, as well as for α-ketoamides and α-ketoesters, the latter two of which have never been successfully applied in umpolung carboxylations with CO
2
(to the best of our knowledge). This reaction features high selectivity, broad substrate scope, good functional group tolerance, mild reaction conditions and facile derivations of products to bioactive compounds, including oxypheonium, mepenzolate bromide, benactyzine, and tiotropium. Moreover, the formation of carbon radicals and carbanions as well as the key role of chlorosilanes are supported by control experiments.
Visible‐light photocatalytic carboxylation with CO2 is highly important. However, it still remains challenging for reluctant substrates with low reduction potentials. Herein, we report a novel ...photocatalytic carboxylation of C−N bonds in cyclic amines with CO2 via consecutive photo‐induced electron transfer (ConPET). It is also the first photocatalytic reductive ring‐opening reaction of azetidines, pyrrolidines and piperidines. This strategy is practical to transform a variety of easily available cyclic amines to valuable β‐, γ‐, δ‐ and ϵ‐amino acids in moderate‐to‐excellent yields. Moreover, the method also features mild and transition‐metal‐free conditions, high selectivity, good functional‐group tolerance, facile scalability and product derivations. Mechanistic studies indicate that the ConPET might be the key to generating highly reactive photocatalysts, which enable the reductive activation of cyclic amines to generate carbon radicals and carbanions as the key intermediates.
A photocatalytic carboxylation of C−N bonds in cyclic amines with CO2 is realized by consecutive photo‐induced electron transfer (ConPET). This mild and transition‐metal‐free protocol provides a general and practical route to valuable β‐, γ‐, δ‐ and ϵ‐amino acids.
Cross-electrophile couplings between two electrophiles are powerful and economic methods to generate C–C bonds in the presence of stoichiometric external reductants. Herein, we report a novel ...strategy to realize the first external-reductant-free cross-electrophile coupling via visible-light photoredox catalysis. A variety of tetraalkyl ammonium salts, bearing primary, secondary, and tertiary C–N bonds, undergo selective couplings with aldehydes/ketone and CO2. Notably, the in situ generated byproduct, trimethylamine, is efficiently utilized as the electron donor. Moreover, this protocol exhibits mild reaction conditions, low catalyst loading, broad substrate scope, good functional group tolerance, and facile scalability. Mechanistic studies indicate that benzyl radicals and anions might be generated as the key intermediates via photocatalysis, providing a new direction for cross-electrophile couplings.
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