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The reaction proves successful starting from C-alkyl nitrones and aryl, hetaryl, alkenyl as well as alkyl aldehydes.

The stability of noble gas (Ng) bound B3+ clusters is assessed via an in silico study, highlighting their structure and the nature of the Ng–B bonds. Ar to Rn atoms are found to form exceptionally strong bonds with B3+ having each Ng–B bond dissociation energy in the range of 15.1–34.8 kcal mol−1 in B3Ng3+ complexes with a gradual increase in moving from Ar to Rn. The computed thermochemical parameters like enthalpy and free energy changes for the Ng dissociation processes from B3Ng3+ also support the stability of Ar to Rn analogues for which the corresponding dissociation processes are endergonic in nature even at room temperature. The covalent nature of the Ng–B bonds is indicated by the localized natural Ng–B bond orbitals and high Wiberg bond indices (0.57–0.78) for Ng–B bonds. Electron density analysis also supports the covalency of these Ng–B bonds where the electron density is accumulated in between Ng and B centres. The orbital interaction energy is the main contributor (ca. 63.0–64.4%) of the total attraction energy in Ng–B bonds. Furthermore, the Ng–B bonding can be explained in terms of a donor–acceptor model where the Ng (HOMO) → B3Ng2+ (LUMO) σ-donation has the major contribution.

Oxidative ring cleavage reactions of furans constitute a group of important transformations that have found wide utility in synthetic organic chemistry. These processes have been used to prepare a variety of 1,4-dicarbonyl compounds including 1,4-dioxoalkenes, 4-oxoalkenals, 4-oxoalkenoic acids, and their derivatives such as 4-hydroxybutenolides and 2,5-dialkoxydihydrofurans. Oxidations of furfuryl alcohols (Achmatowicz reaction) and furfuryl amines (aza-Achmatowicz reaction) provide access to highly functionalized heterocyclic structures that have been employed as intermediates in synthetic routes for the preparation of complex molecules including carbohydrates and alkaloids. Complete oxidative degradation of the furan ring affords carboxylic acids; thus the oxygen heterocycle has served as a masked carboxyl group in many synthetic studies. These transformations and their applications in total syntheses are covered in this chapter. Keywords: Furan; Oxidation; 1,4-Dicarbonyl Compounds; 4-Oxoalkenals; 4-Oxoalkenoic Acids; Carboxylic Acids; Ozone; Singlet Oxygen; Ruthenium Tetroxide; Singlet oxygen; 4-Hydroxybutenolides; Achmatowicz Reaction; Hydrogen Peroxide; N-Bromosuccinimide; tert-Butylhydroperoxide; meta-Chloroperbenzoic Acid; Magnesium Monoperoxyphthalate

DFT-based calculations reveal that the global minimum of IrB12- is a C3v symmetric bowl-like structure in which the Ir atom is located on the concave side of the bowl similar to its lighter congeners, CoB12- and RhB12-.

The reaction of aromatic nitroso derivatives with enolizable carbonyl compounds (nitroso aldol reaction) to give either α-hydroxyamino or α-aminoxy carbonyl compounds is an important synthetic method. This review illustrates the recent advances in rendering the process regio- and enantioselective as well as catalytic. By employing metal and organic catalysts a range of α-amino (α-oxyamination) and α-hydroxy (α-aminoxylation) carbonyl derivatives can be generated with total regioselectivity and high levels of enantiomeric excess. 1 Introduction 2 Metal-Catalyzed Reactions 3 Organocatalyzed Reactions 4 Enamine Metal-Free Reactions 5 Concluding Remarks

The usefulness of aromaticity/antiaromaticity concepts to foresee structural stability patterns and salient features of the electronic structure of small inorganic and all-metal rings has been put forward. A critical revision of the advances made in the theoretical methods to assess the aromaticity/antiaromaticity of these compounds has also been made. In particular, the performance of local versus non-local indices has been reviewed. Finally, the passivation of these rings has been put forward as a key issue in order to prevent them from collapsing into larger aggregates and to provide them protection against the environment.

The concept of aromaticity was initially introduced in chemistry to account for the stability, reactivity, molecular structures, and other properties of many unsaturated organic compounds. Despite that, it has been extended to other species with mobile electrons including saturated systems, transition structures, and even inorganic molecules. In this review, we focus on the aromaticity of a particular family of organometallic compounds known as metallabenzenes, which are characterized by the formal replacement of a CH group in benzene by an isolobal transition metal fragment. In addition, aromaticity of related compounds such as heterometallabenzenes is considered as well. To this end, we shall describe herein the insight gained by the available experimental data as well as by the application of the state-of-the-art computational methods developed as descriptors for aromaticity together with a critical evaluation of their performance to quantitatively estimate the strength of aromaticity of these systems.

This work was supported by the Ministerio de Ciencia e Innovacion (MICINN) and FEDER Program (Madrid, Spain, project CTQ2013-44367-C2-1-P) and the Gobierno de Aragon (Zaragoza, Spain. D.R.-L. thanks the Spanish Ministry of Education (MEC) for a pre-doctoral grant (FPU program). We thank the Italian Ministry of University and Scientific Research (MIUR) for a doctoral grant and the University of Calabria for financial support.

Two highly stereoselective radical-mediated syntheses of densely functionalized indanes and dibenzocycloheptadienes from ortho-vinyl- and ortho-vinylaryl-substituted N-(arylsulfonyl)-acrylamides, respectively, are presented.

The addition of a variety of radicals to the double bond of N-(arylsulfonyl)acrylamides can trigger cyclization/aryl migration/desulfonylation cascades via amidyl radical intermediates 2. Herein, we demonstrate the synthetic utility of these intermediates in subsequent C–C and C–X bond-forming events to rapidly build up molecular complexity. First, we describe a regioselective one-pot synthesis of CF3-, SCF3-, Ph2(O)P-, and N3-containing indolo[2,1-a]isoquinolin-6(5H)-ones from N-[(2-ethynyl)arylsulfonyl]acrylamides through a multi-step radical reaction cascade. The process involves the one-pot formation of four new bonds (one C–X, two C–C, and one C–N), a formal 1,4-aryl migration, and desulfonylation of the starting material. Second, we present a one-pot synthesis of 3,3-disubstituted-2-dihydropyridinones from N-(arylsulfonyl)acrylamides and 1,3-dicarbonyl compounds. In this case, a silver-catalyzed radical cascade process involving the sequential formation of two new C–C bonds and one C–N bond, a forma...

The aminofluorination of alkenes has become an attractive platform for the synthesis of β-amino-fluorinated compounds, valuable building blocks in medicinal and agricultural chemistry. The novel methodologies disclosed in recent years have unraveled a broad array of reaction mechanisms, so that the interest in these transformations transcends the mere synthetic aspects. This review aims to summarize the most relevant findings in this area attending at the nature of the fluorine source, and thus the specific mechanism operating in each of these transformations, namely electrophilic, nucleophilic, radical, and late transition metal-catalyzed reactions.

Cyclic nitrones (I), (IV), and (VI) give the products as single diastereomers under thermal conditions while nitrones (VIII) and (X) derived from D-glyceraldehyde and D-galactose give mixtures of diastereomers.

Review: recent methodologies for the simultaneous formation of C—CF3 and C—C or C-heteroatom bonds by formal addition reactions to alkenes; 70 refs.

Two radical-mediated processes of activated alkenes, namely arylphosphonylation and arylazidation, are described. The difunctionalization of alkenes by a tandem process that involves radical addition, 1,4-aryl migration, and desulfonylation generates α-aryl-β-heterofunctionalized amides bearing a quaternary stereocenter when the substituent on the nitrogen atom is an aryl group. Alternatively, heterooxindoles or spirobicycles can be obtained with excellent regioselectivity in the presence of an alkyl substituent on the nitrogen atom.

This review will describe the recent advances in the synthesis of C-nucleosides with inhibitory activity of inosine monophosphate dehydrogenase (IMPDH), a key enzyme in the biosynthesis of guanine nucleotides. The review will cover synthetic approaches of structural analogues showing modifications in the furanose ring as well as in the heterocyclic base. Heterocyclic sugar nucleoside analogues in which the furanose ring has been replaced by a different heterocyclic ring including aza analogues, thioanalogues as well as dioxolanyl and isoxazolidinyl analogues are also considered.

The potential energy surfaces of the singlet and triplet states of the title clusters are computed by DFT methods.

Bu4NI is able to activate Togni reagent (II) to generate a highly reactive iodine (III) species, which smoothly reacts with alkenes to form a new C—CF3 bond.

The reaction affords α-aryl-βtrifluoromethylamides with a quaternary stereocenter or trifluoromethylated oxindoles from the N-aryl or N-alkyl substrates of the types (I) or (X), respectively.

The diastereoselective 1,3-dipolar cycloadditions of achiral nitrones (I) with chiral acrylamide (II) is compared with the corresponding cycloadditions of chiral nitrones (V) with methyl acrylate.

2-Aza-Cope rearrangements under neutral conditions are investigated by kinetic 1H NMR experiments.

Control over molecular motion represents an important objective in modern chemistry. Aromatic azobenzenes are excellent candidates as molecular switches since they can exist in two forms, namely the cis (Z) and trans (E) isomers, which can interconvert both photochemically and thermally. This transformation induces a molecular movement and a significant geometric change, therefore the azobenzene unit is an excellent candidate to build dynamic molecular devices. We describe selected examples of systems containing an azobenzene moiety and their motions and geometrical changes caused by external stimuli.

In a mechanistically-oriented study, O-α-allenyl esters have been evaluated as potential substrates for Pd-catalyzed carbopalladation/allylic alkylation domino sequences and decarboxylative allenylation reactions. The domino sequence turned out to be feasible only with electron-deficient aryl iodides, thereby showing a narrower potential than that previously observed with the malonamide-based series. The decarboxylative allenylation of O-α-allenyl esters was also tested and turned out to be practicable with β-ketoester-based substrates and using specific basic conditions. Plausible reaction mechanisms are proposed to account for the observed reactivities.

A highly efficient route for the synthesis of valuable 3,4-substituted chromenone derivatives by the reaction of 1,3-diketones with aldehydes in the presence of L-proline was developed. The reactions take advantage of readily available starting materials and follow a Knoevenagel condensation/Michael addition/hemiacetalization domino process. Chiral 3-substituted chromenones are obtained with high enantioselectivities when a chiral diarylprolinol TMS-ether is applied in the reaction.

The asymmetric cyclization of cyclic β-diketones with α,β-unsaturated aldehydes is efficiently catalyzed by diarylprolinol silyl ethers to afford hydroxychromenone derivatives, e.g. (III), in good yields and enantioselectivities.

Ring-closing metathesis reactions of dialkenyl amines, amides and carbamates catalyzed by Ru-catalysts provide efficient approaches to six-membered nitrogen heterocyclic compounds, which are precursors of a variety of natural products and related compounds. Abstract Monoterpene indole alkaloids comprise a group of naturally occurring compounds, exhibiting a range of biological activities. These compounds have attracted great attention because of their interesting biosynthetic route and also as a challenging target for total synthesis. For such synthetic approach and structure - activity relationship studies, the knowledge about their absolute stereostructures is essential. This review summarizes the presently available results of studies on the determination of the absolute configuration of indole alkaloids by the use of circular dichroism (CD).

Formal [3 + 2] cycloaddition of electron-deficient alkenes with in situ generated nitrone ylides provides an efficient access towards all-cis-N-hydroxypyrrolidines (III) and (VI) in good diastereoselectivity (usually more than 80% d.e.).

A series of enantiopure five-membered cyclic nitrones (III) is synthesized through asymmetric Michael addition of enolizable aldehydes to nitroalkenes followed by one-pot Zn-promoted reductive cyclization.

A variety of enantioenriched β-nitrophosphonates (III) is readily obtained by asymmetric Michael addition of diphenylphosphite (II) to nitroolefins (I) in the presence of a bifunctional amine—thiourea organocatalyst.

The asymmetric Michael addition of acetone to nitroolefins in the presence of various proline related catalysts is investigated.

Born-Oppenheimer molecular dynamics simulations and high-level quantum chemical computations (B3LYP, MP2, CCSD(T)) reveal the starlike D5h C5Al5- global minimum with five planar tetracoordinate carbon atoms to be a promising candidate for detection by photoelectron detachment spectroscopy.

Recent advances in the organocatalytic enantioselective synthesis of γ-nitrocarbonyl compounds through Michael additions of either nitroalkanes to α,β-unsaturated carbonyl derivatives or enolizable carbonyl compounds to nitroalkenes are surveyed. Domino processes leading to structurally more complex products bearing the γ-nitrocarbonyl functionality are also reviewed.

A broad spectrum of polysubstituted dihydrofuran skeletons is available with a high functional group tolerance.

The microwave-assisted method is based on the use of allyl Hantzsch ester AHE as hydride source and chiral N-triflyl phosphoramide PHA as organocatalyst.

This greatversatility in scope and applicability in different fieldsincluding fine chemicals, polymer chemistry, and the phar-maceutical industry justify the crucial role of arylboronates inthe synthesis of aromatic compounds. Indeed, arylboronatescanbeassembledeasilywithhighefficiencyunderavarietyofreaction conditions. Nevertheless, the potential use of aryl-boronates in the construction of complex molecules resides inthe presence of a diverse and adequate number of function-alities; because of this, the synthesis of functionalizedarylboronates constitutes a challenging research area.Arylboronates are accessible from the parent boronicacids—that can be prepared by reaction of trialkyl borateswith Grignard or lithium reagents—by treatment withalcohols or diols in organic solvent.

A new two-step sequence involves reaction of α-ketols with isocyanates and subsequent oxidative cleavage of the exocyclic double bond according to A) or B) to give the title compounds.

A five-step synthesis of O,N-protected (+)-3-deoxynojirimycin (7a) and (+)-3-deoxymannojirimycin (7b) from N-Boc L-serinal acetonide (1) employing 2-acetylthiazole (2) as a masked α-hydroxypropanal β-anion synthon is described.