Multiple Bond Formation Research Articles

PEG1000-Based Dicationic Acidic Ionic Liquid Catalyzed One-pot Synthesis of 1,4-Dihydropyridines via the Hantzsch Reaction

Devising reactions that achieve multiple-bond formation in one operation has become one of the major challenges in the search for efficient syntheses. Multi-component reactions (MCRs) allow the cre...

ChemInform Abstract: Gold‐Catalyzed Cascade Reactions of Alkynes for Construction of Polycyclic Compounds

AbstractReview: [65 refs.

Reactions in nitroimidazole triggered by low-energy (0-2 eV) electrons: methylation at N1-H completely blocks reactivity.

Low-energy electrons (LEEs) at energies of less than 2 eV effectively decompose 4-nitroimidazole (4NI) by dissociative electron attachment (DEA). The reactions include simple bond cleavages but also complex reactions involving multiple bond cleavages and formation of new molecules. Both simple and complex reactions are associated with pronounced sharp features in the anionic yields, which are interpreted as vibrational Feshbach resonances acting as effective doorways for DEA. The remarkably rich chemistry of 4NI is completely blocked in 1-methyl-4-nitroimidazole (Me4NI), that is, upon methylation of 4NI at the N1 site. These remarkable results have also implications for the development of nitroimidazole based radiosensitizers in tumor radiation therapy.

Gold‐Catalyzed Cascade Reactions of Alkynes for Construction of Polycyclic Compounds

AbstractThe development of cascade reactions is an area of considerable interest in modern organic chemistry. Efficient cascade reactions realize the economical synthesis of complex target molecules through multiple bond formations in a single operation. Elementary reactions that form fewer waste products are desirable in terms of atom economy and in order to suppress side product formation in sequential processes. Recent advances in homogeneous gold catalysis have opened up further possibilities for cascade reactions. In this review, recent advances in gold‐catalyzed cascade cyclizations of alkynes are summarized. In particular, cascade reactions based on nucleophilic/electrophilic addition, carbene cyclopropanation/insertion, ring expansion, and cycloaddition are highlighted. Notably, many of the cascade reactions shown in this mini‐review feature no theoretical waste products.

Tuning Uranium–Nitrogen Multiple Bond Formation with Ancillary Siloxide Ligands

The new homoleptic ate U(III) siloxide [K(18c6)][U(OSi(O(t)Bu)3)4] 2 was prepared in 69% yield by reduction of [U(OSi(O(t)Bu)3)4] 3 with KC8. The reaction of the neutral U(III) siloxide complex [U(OSi(O(t)Bu)3)2(μ-OSi(O(t)Bu)3)]2 1 with adamantyl azide leads to the isolation of the dinuclear U(VI) imido complex [U2(NAd)4(OSi(O(t)Bu)3)4] 4. The X-ray crystal structure shows the presence of a "cation-cation interaction" between the two [U(NAd)2](2+) groups. In contrast the reactions of 2 with the trimethylsilyl and adamantyl azides afford the U(V) imido complexes [K(18c6)][U(NSiMe3)(OSi(O(t)Bu)3)4] 5-TMS and [K(18c6)][U(NAd)(OSi(O(t)Bu)3)4] 5-Ad pure in 48% and 66% yield, respectively. The reaction of 2 with CsN3 in THF at -40 °C yields a mixture of products from which the azido U(IV) complex [K(18c6)][U(N3)(OSi(O(t)Bu)3)4] 7 and the μ-nitrido diuranium(V) complex [KU(μ-N)(OSi(O(t)Bu)3)]2 8 were isolated. The crystal structure of 8 shows the presence of a rare U2N2 core with two nitrido atoms bridging two uranium centers in a diamond-shaped geometry. In contrast, the reaction of 1 with CsN3 affords the diuranium(IV) complex Cs{(μ-N)[U(OSi(O(t)Bu)3)3]2} 9 presenting a nitrido ligand bridging two uranium and one cesium cations. These results show the importance of the coordination environment in the outcome of the reaction of U(III) with azides.

ChemInform Abstract: Recent Advances in the Construction of Polycyclic Compounds by Palladium‐Catalyzed Atom‐Economical Cascade Reactions

AbstractReview: 108 refs.

STM imagery and density functional calculations of C60fullerene adsorption on the 6H-SiC(0001)-3×3 surface

Scanning tunneling microscopy (STM) studies of the fullerene C${}_{60}$ molecule adsorbed on the silicon carbide SiC(0001)-$3\ifmmode\times\else\texttimes\fi{}3$ surface, combined with density functional theory (DFT) calculations, show that chemisorption of individual C${}_{60}$ molecules occurs through the formation of one bond to one silicon adatom only in contrast to multiple bond formation on other semiconducting surfaces. We observe three stable adsorption sites with respect to the Si adatoms of the surface unit cell. Comprehensive DFT calculations give different adsorption energies for the three most abundant sites showing that van der Waals forces between the C${}_{60}$ molecule and the neighboring surface atoms need to be considered. The C${}_{60}$ molecules are observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and nonnegligible intermolecular interactions.

ChemInform Abstract: Highly Efficient Synthesis of Multisubstituted Furans Through Cupric Halide Mediated Intramolecular Halocyclization of 1‐(1‐Alkynyl)cyclopropyl Ketones.

A convenient and efficient method for the synthesis of 3-halofurans was developed by using a cascade reaction between 1-(1-alkynyl)cyclopropyl ketones and cupric halide. Under mild reaction conditions, both 3-chloro- and 3-bromofuran derivatives were obtained in high yields. The reaction involves consecutive multiple bond formations, includingC–O and C–Br bonds, with high regioselectivity. Mechanistic aspects are described.

Cascade Syntheses Routes to the Centrocountins

Cascade and domino reactions that proceed through multiple steps in one pot and include multiple bond formations are promising methods for the rapid and efficient generation of complex molecular architectures, including the scaffolds of classes of complex natural product. We describe the development of various one-pot cascade reaction sequences to yield centrocountins, which are tetracyclic indole derivatives with the basic scaffold of numerous polycyclic alkaloids. The mechanistic investigation of a sequence employing readily available alkynes and 3-formylchromones as starting materials provided evidence that this one-pot synthesis proceeds through at least twelve consecutive transformations and includes at least nine different chemical reactions, making it the longest cascade reaction sequence known to date. We describe the scope and limitations of the cascade synthesis approaches and the development of an enantioselectively catalyzed centrocountin synthesis.

ChemInform Abstract: Indium Triflate Catalyzed One‐Pot Multicomponent Synthesis of Spiro‐Hexahydropyrimidines Explained by Multiple Covalent Bond Formation.

AbstractThe process includes 6 molecules of reactants and 6 new covalent bonds are generated in the presence of a reusable catalyst.

Recent Advances in the Construction of Polycyclic Compounds by Palladium‐Catalyzed Atom‐Economical Cascade Reactions

AbstractThe development of cascade reactions that realize step‐economical syntheses of complex compounds by multiple bond formation is one of the most attractive subjects in modern organic chemistry. Another important challenge in this area is to improve atom economy by minimizing waste product formation and avoiding prefunctionalization of the substrates. Because palladium catalysts are well known to promote a variety of atom‐economical elementary reactions, many useful palladium‐catalyzed cascade reactions have been developed. In this Focus Review, recent advances in palladium‐catalyzed atom‐economical cascade reactions for the construction of polycyclic compounds are summarized. Especially, the cascade reactions reported in the past decade, which include carbopalladation onto alkyne/alkene/allenes, nucleophilic reaction, and direct arylation/CH bond functionalization, are highlighted.

Indium triflate catalyzed one-pot multicomponent synthesis of spiro-hexahydropyrimidines explained by multiple covalent bond formation

A mild, efficient, and expeditious method has been developed for the synthesis of spiro-hexahydropyrimidine derivatives via a three-component, one-pot cyclocondensation reaction of aromatic amines, formaldehyde, and cyclic ketones in 4–6h using In(OTf)3 as Lewis acid catalyst for the first time. The reaction involving creation of six new covalent bonds was efficiently promoted by 10mol% In(OTf)3 and the catalyst could be recovered easily after the reaction and reused without any loss of its catalytic activity. The advantageous features of this methodology are high atom-economy, operational simplicity, shorter reaction time, and easy handling.

ChemInform Abstract: Preparation of Quinazolino[3,2‐a]quinazolines via a Palladium‐Catalyzed Three‐Component Reaction of Carbodiimide, Isocyanide, and Amine.

AbstractTitle reaction involves multiple bond formations in one‐pot through nucleophilic attack, isocyanide insertion, and C‐N coupling steps.

Highly Efficient Synthesis of Multisubstituted Furans through Cupric Halide‐Mediated Intramolecular Halocyclization of 1‐(1‐Alkynyl)cyclopropyl Ketones

AbstractA convenient and efficient method for the synthesis of 3‐halofurans was developed by using a cascade reaction between 1‐(1‐alkynyl)cyclopropyl ketones and cupric halide. Under mild reaction conditions, both 3‐chloro‐ and 3‐bromofuran derivatives were obtained in high yields. The reaction involves consecutive multiple bond formations, includingC–O and C–Br bonds, with high regioselectivity. Mechanistic aspects are described.

Ir3Co6 and Co3Fe3 Dithiolene Cluster Complexes: Multiple Metal–Metal Bond Formation and Correlation between Structure and Internuclear Electronic Communication

π-Conjugated trinuclear iridium and cobalt dithiolenes undergo multiple metal-metal bond formation with Co(2)(CO)(8) and Fe(CO)(5), giving rise to Ir(3)Co(6) nonanuclear and Co(3)Fe(3) hexanuclear cluster complexes 5 and 6, respectively. 5 retains a planar framework and intense π conjugation across the three iridadithiolenes and the phenylene bridge, which results in intense electronic communication among the three Co(2)(CO)(5) units in reduced mixed-valent states.

ChemInform Abstract: Recent Advances in Palladium‐Catalyzed Cascade Cyclizations

AbstractReview: 140 refs.

Gas-Bubble Effects on the Formation of Colloidal Iron Oxide Nanocrystals

This paper reports that gas bubbles can be used to tailor the kinetics of the nucleation and growth of inorganic-nanocrystals in a colloidal synthesis. We conducted a mechanistic study of the synthesis of colloidal iron oxide nanocrystals using gas bubbles generated by boiling solvents or artificial Ar bubbling. We identified that bubbling effects take place through absorbing local latent heat released from the exothermic reactions involved in the nucleation and growth of iron oxide nanocrystals. Our results show that gas bubbles display a stronger effect on the nucleation of iron oxide nanocrystals than on their growth. These results indicate that the nucleation and growth of iron oxide nanocrystals may rely on different types of chemical reactions between the iron-oleate decomposition products: the nucleation relies on the strongly exothermic, multiple-bond formation reactions, whereas the growth of iron oxide nanocrystals may primarily depend upon single-bond formation reactions. The identification of exothermic reactions is further consistent with our results in the synthesis of iron oxide nanocrystals with boiling solvents at reaction temperatures ranging from 290 to 365 °C, by which we determined the reaction enthalpy in the nucleation of iron oxide nanocrystals to be -142 ± 12 kJ/mol. Moreover, our results suggest that a prerequisite for effectively suppressing secondary nucleation in a colloidal synthesis is that the primary nucleation must produce a critical amount of nuclei, and this finding is important for a priori design of colloidal synthesis of monodispersed nanocrystals in general.

Recent Advances in Palladium‐Catalyzed Cascade Cyclizations

AbstractThe importance of palladium‐catalyzed cross coupling reactions in contemporary organic synthesis is undisputed and underlined by the Nobel Prize for Chemistry in 2010. In addition to the highly efficient cross coupling reactions for single CC bond construction, palladium‐catalyzed cascade processes involving multiple bond formations have emerged in recent years as valuable tools for the rapid synthesis of complex molecular scaffolds. This review presents an overview of the most relevant developments in this field, with a focus on the generation of diverse poly‐ and heterocyclic scaffolds. The generally well understood reactivity of palladium has allowed the discovery of many intriguing novel cascade processes, and the creativity of the synthetic community will undoubtedly lead to many more discoveries in the future.

ChemInform Abstract: Synthetic Evolutions in the Nucleophilic Addition to Alkynes

AbstractReview: 65 refs.

ChemInform Abstract: Enzymatic Cyclizations Using Laccases: Multiple Bond Formation Between Dihydroxybenzoic Acid Derivatives and Aromatic Amines.

AbstractThe laccase‐catalyzed cyclization of dihydroxybenzoic acid derivatives (I) with amino‐carboxamides leads to a variety of fused diazepines in low to moderate yields.