Atom-economic Reaction Research Articles

Scope and Limitations of the Domino Vinylogous Aldol/oxa‐Michael Reaction

AbstractThe asymmetric, atom economic reaction of salicylaldehydes with α,β‐unsaturated aldehydes in the presence of an organocatalyst leads to chiral tricyclic chromanes. In this report, the first exploration of heteroatom‐substituted α,β‐unsaturated aldehydes is demonstrated: We present the investigation of the enantioselective domino vinylogous aldol/oxa‐Michael reaction in respect to its scope and limitations. The chiral chromanes arriving from this reaction are highly functionalized and are versatile synthetic intermediates that can further be converted into the respective tetrahydroxanthones with functionalities on the C‐4a position. A new synthetic route to a methyl ester on this position is developed starting with a p‐methoxyphenyl protected alcohol.

Cp*Rh(III)-Catalyzed Mild Addition of C(sp3)-H Bonds to α,β-Unsaturated Aldehydes and Ketones.

A Rh(III)-catalyzed addition of benzylic C(sp3)-H bond to α,β-unsaturated ketones/aldehydes has been realized, leading to efficient synthesis of γ-aryl ketones/aldehydes. This atom-economic reaction proceeded under mild and redox-neutral conditions with a broad substrate scope. Besides benzylic C-H, allylic C-H bonds are also applicable when assisted by O-methyl ketoxime directing groups.

Charged Covalent Triazine Frameworks for CO2 Capture and Conversion.

The quest for the development of new porous materials addressing both CO2 capture from various sources and its conversion into useful products is a very active research area and also critical in order to develop a more sustainable and environmentally-friendly society. Here, we present the first charged covalent triazine framework (cCTF) prepared by simply heating nitrile functionalized dicationic viologen derivatives under ionothermal reaction conditions using ZnCl2 as both solvent and trimerization catalyst. It has been demonstrated that the surface area, pore volume/size of cCTFs can be simply controlled by varying the synthesis temperature and the ZnCl2 content. Specifically, increasing the reaction temperature led to controlled increase in the mesopore content and facilitated the formation of hierarchical porosity, which is critical to ensure efficient mass transport within porous materials. The resulting cCTFs showed high specific surface areas up to 1247 m2 g-1, and high physicochemical stability. The incorporation of ionic functional moieties to porous organic polymers improved substantially their CO2 affinity (up to 133 mg g-1, at 1 bar and 273 K) and transformed them into hierarchically porous organocatalysts for CO2 conversion. More importantly, the ionic nature of cCTFs, homogeneous charge distribution together with hierarchical porosity offered a perfect platform for the catalytic conversion of CO2 into cyclic carbonates in the presence of epoxides through an atom economy reaction in high yields and exclusive product selectivity. These results clearly demonstrate the promising aspect of incorporation of charged units into the porous organic polymers for the development of highly efficient porous organocatalysts for CO2 capture and fixation.

Organocatalyzed coupling of carbon dioxide with epoxides for the synthesis of cyclic carbonates: catalyst design and mechanistic studies

The coupling of carbon dioxide (CO2) with epoxides with the formation of cyclic carbonates is a highly attractive 100% atom economic reaction. It represents a greener and safer alternative to the conventional synthesis of cyclic carbonates from diols and toxic phosgene.

An atom- and pot-economical consecutive multi-step reaction approach to polycyclic aromatic hydrocarbons (PAHs).

A novel one-pot benzannulation reaction has been developed for the synthesis of substituted polycyclic aromatic hydrocarbons (PAHs) from the direct coupling of propargylic aldehydes/alcohols with 1,1-diarylethanol through an atom-economical uninterrupted three/four-step reaction sequence under mild and metal-free reaction conditions. The strategy involves an acid-catalyzed dehydration and carbon-carbon bond formation followed by DBU-promoted cycloisomerization. Naphthalene and phenanthrene were obtained via mono-benzannulation, and chrysene, picene and benzopicene were obtained involving consecutive di-benzannulation reactions in good yields starting from easily accessible starting materials.

Organocatalyzed Synthesis of Oleochemical Carbonates from CO2 and Renewables.

Bifunctional phosphorus-based organocatalysts proved to be highly efficient for the atom-economic reaction of CO2 and epoxidized oleochemicals. Notably, those products are obtained from CO2 and renewable feedstocks only. Structure-activity relationships have been deduced from a screening of 22 organocatalysts in a test reaction. Bifunctional catalysts based on a phosphonium salt bearing a simple phenolic moiety proved to be extraordinarily active under comparatively mild and solvent-free reaction conditions. In the presence of the most active organocatalyst 12 oleochemical carbonates were isolated in excellent yields up to 99 %. This organocatalyzed reaction represents an excellent example for the realization of the 12 Principles of Green Chemistry as well as the 12 Principles of CO2 Chemistry.

Hydrophosphination of Unactivated Alkenes and Alkynes Using Iron(II): Catalysis and Mechanistic Insight

The catalytic addition of phosphines to alkenes and alkynes is a very attractive process that offers access to phosphines in a 100% atom-economic reaction using readily available and inexpensive materials. The products are potentially useful ligands and organocatalysts. Herein, we report the first example of intramolecular hydrophosphination of a series of nonactivated phosphinoalkenes and phosphinoalkynes with a simple iron β-diketiminate complex. Kinetic studies suggest that this transformation is first-order with respect to both the phosphine and the catalyst. A mechanistic interpretation of the iron-catalyzed hydrophosphination is presented, supported by the experimental evidence collected.

Synthesis of 3-Indolylglycine Derivatives via Dinuclear Zinc Catalytic Asymmetric Friedel-Crafts Alkylation Reaction.

A direct asymmetric Friedel-Crafts (F-C) alkylation reaction between a wide range of indoles and ethyl 2-(4-methoxyphenylimino)acetate catalyzed by Trost's dinuclear complex is reported. A series of 3-indolylglycine derivatives were synthesized in enantioselectivity of up to >99% enantiomeric excess (ee) using 10 mol% catalyst loading under mild conditions. This atom economic reaction could be run on a gram scale without impacting its enantioselectivity. The absolute stereochemistry of catalytic products was determined by correlation with a known configuration compound. A possible mechanism was proposed for the asymmetric induction.

Cobalt-Catalyzed Synthesis of Aromatic, Aliphatic, and Cyclic Secondary Amines via a “Hydrogen-Borrowing” Strategy

The replacement of precious metals with inexpensive, less toxic, and earth-abundant elements in typical noble-metal-mediated organic transformations is a major goal in current synthetic chemistry and industries. The metal-catalyzed N-alkylation of amines with other amines through a “hydrogen-borrowing” principle represents a green and atom-economical reaction for the synthesis of secondary amines. However, catalysts developed thus far that are effective for this process remain quite scarce and are only limited to a few ruthenium and iridium complexes. In this work, we present a cobalt-catalyzed selective alkylation of amines with amines to synthesize a large variety of secondary amines. A range of amine substrates have been converted to the corresponding products through hetero- or homocoupling between amines. Cyclic sec-amines are also achieved from diamine precursors as rare examples.

Synthesis of 6-Substituted 2-Pyrones Starting from Renewable Resources: Total Synthesis of Sibirinone, (E)-6-(Pent-1-en-1-yl)-2H-pyran-2-one, and (E)-6-(Hept-1-en-1-yl)-2H-pyran-2-one.

An atom-economic reaction sequence to 6-substituted 2-pyrones was developed starting from furfuryl alcohol, a renewable resource made from bran or bagasse, and aldehydes, utilizing a thermal rearrangement of cyclopentadienone epoxides as key step. Derivatives bearing a hydroxyalkyl side chain could be enzymatically resolved, providing access to enantiomerically pure 2-pyrones, or converted to alkenyl-substituted 2-pyrones such as naturally occurring sibirinone, (E)-6-(pent-1-en-1-yl)-2H-pyran-2-one, and (E)-6-(hept-1-en-1-yl)-2H-pyran-2-one.

ChemInform Abstract: Carbonylations of Alkenes in the Total Synthesis of Natural Compounds

AbstractReview: [121 refs.

A new synthetic strategy to 2,3-diallyl-1,4-quinones via one-pot double Claisen rearrangement and retro Diels–Alder reaction

A simple and an efficient synthetic strategy to 2,3-diallyl-1,4-quinone derivatives via a highly reliable and 100% atom economic reactions such as Diels–Alder (DA) reaction, Claisen rearrangement (CR), and retro Diels–Alder (rDA) reaction as key steps is reported.

Carbonylations of Alkenes in the Total Synthesis of Natural Compounds

The goal of this review is to highlight the applications of carbonylation reactions of alkenes in the total synthesis of natural compounds. These highly atom-economic reactions, which are known for their industrial applications, constitute attractive synthetic methodologies for the selective construction of carbonyl compounds. We aimed at the selection of recent methodologically attractive syntheses where carbonylations were applied as key steps. In addition, a few examples of the related carbonylation of allenes are shown. 1 Introduction 2 Hydroformylation 3 Hydroaminomethylation and Related Tandem Hydroformylation Reactions 4 Reppe Carbonylation 5 Allylic Carbonylation 6 Oxidative Carbonylation 7 Pauson–Khand Reaction 8 Summary and Outlook

Dual C–H/C–H asymmetric cross-coupling unveiled

Although chemists have turned modifying unreactive C–H bonds into a routine event in organic synthesis, now and again a new approach still turns up. In one of the latest examples, De-Wei Gao, Qing Gu, and Shu-Li You of Shanghai Institute of Organic Chemistry have reported an asymmetric twofold C–H oxidative cross-coupling reaction of ferrocenes with heteroarenes that takes place without having to first prefunctionalize one or the other aryl coupling partners, which is usually required in cross-coupling strategies (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b00127). The new reaction is a greener, less expensive method for preparing planar chiral ferrocenes, which are useful as chiral ligands and as asymmetric catalysts, You says. The team’s strategy involves a palladium catalyst with a protected chiral amino acid ligand that proceeds in a twofold manner, first activating the ferrocene and then the heteroarene. The atom-economical reaction avoids the need for an aryl halide or

ChemInform Abstract: Contemporaneous Dual Catalysis: Aldol Products from Non‐Carbonyl Substrates.

AbstractVanadium‐catalyzed 1,3‐transposition of allenols is coupled with a lanthanum‐catalyzed Meinwald rearrangement of epoxides in situ to form aldol products chemo‐, regio‐, and stereoselectively.

Polymer supported DMAP: an easily recyclable organocatalyst for highly atom-economical Henry reaction under solvent-free conditions

Polymer supported catalysts are regarded as a borderline class of catalysts, which retains the advantages of homogeneous catalysts while securing the ease of recovery by simple filtration and workup of heterogeneous systems.

A concise and atom-economical Suzuki-Miyaura coupling reaction using unactivated trialkyl and triarylboranes with aryl halides

A concise and atom-economical Suzuki-Miyaura coupling reaction using unactivated trialkyl and triarylboranes with aryl halides

Calcium carbide as a convenient acetylene source in the synthesis of unsaturated sulfides, promising functionalized monomers

Calcium carbide was studied as a useful solid-state reagent to incorporate acetylene unit into synthetic procedures. Atom-economic thiol-yne click reaction was successfully performed with single and double additions. Heterocyclic thiols and aliphatic dithiols reacted with acetylene generated in situ from calcium carbide to afford corresponding vinyl sulfides and bis(thiovinyl)ethers in good to high yields.

Z‐Selective Hydrothiolation of Racemic 1,3‐Disubstituted Allenes: An Atom‐Economic Rhodium‐Catalyzed Dynamic Kinetic Resolution

A Z-selective rhodium-catalyzed hydrothiolation of 1,3-disubstituted allenes and subsequent oxidation towards the corresponding allylic sulfones is described. Using the bidentate 1,4-bis(diphenylphosphino)butane (dppb) ligand, Z/E-selectivities up to >99:1 were obtained. The highly atom-economic desymmetrization reaction tolerates functionalized aromatic and aliphatic thiols. Additionally, a variety of symmetric internal allenes, as well as unsymmetrically disubstituted substrates were well tolerated, thus resulting in high regioselectivities. Starting from chiral but racemic 1,3-disubstituted allenes a dynamic kinetic resolution (DKR) could be achieved by applying (S,S)-Me-DuPhos as the chiral ligand. The desired Z-allylic sulfones were obtained in high yields and enantioselectivities up to 96 % ee.

Contemporaneous Dual Catalysis: Aldol Products from Non-Carbonyl Substrates.

The aldol reaction represents an important class of atom-economic carbon-carbon bond-forming reactions vital to modern organic synthesis. Despite the attention this reaction has received, issues related to chemo- and regioselectivity as well as reactivity of readily enolizable electrophiles remain. To help overcome these limitations, a new direct approach toward aldol products that does not rely upon carbonyl substrates is described. This approach employs room-temperature contemporaneous lanthanum/vanadium dual catalysis, whereby a vanadium-catalyzed 1,3-transposition of allenols is coupled with a lanthanum-catalyzed Meinwald rearrangement of epoxides in situ to directly form aldol products.