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Palladium-catalyzed ring-opening reactions of C1 substituted 7-oxanorbornadiene derivatives with aryl iodides were investigated. The optimal conditions for this reaction were found to be PdCl2(PPh3)2, ZnCl2, Et3N and Zn in THF. Both steric and electronic factors played a role in the outcome of the reaction as increasing the steric bulk on the bridgehead carbon decreased the yield. These reactions were found to be highly regioselective, giving only one of the two possible regioisomers in all cases. A diverse collection of novel, highly substituted biphenyl derivatives were obtained.

A safer and improved method to our previous report on palladium-catalyzed cyclopropanation of heterobicyclic alkenes has been developed. By using tetrahydrofuran as the solvent and a more dilute aqueous NaOH solution for the generation of diazomethane from Diazald, cyclopropanation could be achieved smoothly with minimal adjustment over the course of reaction. 7-Oxabicyclic substrates with bulky C1 or C2 groups, as well as 2,3-diazabicyclic substrates with various N-substituents, effectively underwent cyclopropanation. Using this methodology, yields to previously reported products were markedly increased, and 10 new cyclopropanated [2.2.1] heterobicyclic products were prepared. In addition, this work accounts for the first reported cyclopropanation of 2,3-diazabicyclic alkenes, which all gave excellent yields of >90%.

Key step of the improved synthesis of title compound (VIII) is the Kulinkovich cyclopropanation, and subsequent oxidative fragmentation of the cyclopropanol (IV).

The synthesis of “precision” polymers with fi nely controlled molecular structures is an important new development in synthetic polymer chemistry. This trend is the logical outcome of the continuing evolution of the fi eld of polymer synthesis. Indeed, during the last few decades, synthetic tools, such as living ionic polymerizations, controlled radical polymerizations, and click chemistry, have revolutionized the synthesis of polymers with controlled architectures such as block, graft, star, brush, hyperbranched or cyclic polymers. These aspects being solved, it is now time for polymer chemists to address more challenging questions such as the design of monodisperse polymers and the control of primary (i.e., comonomer sequences), secondary (i.e., single-chain folding), and tertiary (i.e., single-chain compartmentalization) structures. Here, new synthetic tools have to be developed or imported from other disciplines such as organic chemistry and biochemistry. For instance, solid-phase iterative chemistry, which was initially introduced for the synthesis of oligopeptides and oligonucleotides, is an interesting methodology for preparing monodisperse sequence-defi ned polymers. However, such approaches are usually time-consuming and request demanding coupling/capping/ deprotection steps. Yet, interesting protecting-group-free methodologies have been described in recent years for simplifying and accelerating these processes. These promising new approaches are briefl y listed and explained in this article.

An optimized condition for the rhodium-catalyzed ring-opening reaction of C1-substituted oxabicyclic alkenes with aryl boronic acids was developed and the effect of aryl boronic acid as well as the effect of C1 substitution on the oxabicyclic alkenes was studied. Aryl boronic acids carrying electron-donating substituents provided the ring-opened products in excellent yields regardless of the position, while electron-withdrawing substituents were more susceptible to steric interactions. Although two different regioisomers are possible, all the rhodium-catalyzed ring-opening reactions of C1 substituted oxabicyclic alkenes studied with aryl boronic acids were found to be highly regioselective, giving single regioisomers in all cases.

Ruthenium-catalyzed asymmetric [2 + 2] cycloadditions between chiral acyl camphorsultam-functionalized alkynes and bicyclic alkenes were examined, providing adducts with complete exo stereoselectivity in good overall yield and enantioselectivity (up to 99% and 166:1, respectively), as well as appreciable diastereoselectivity (up to 163:1). The diastereoselectivity showed dependence on the solvent and temperature, as well as on the substitution pattern of the reacting alkyne and bicyclic alkene components. In general, higher diastereoselectivities were observed for reactions conducted in ethereal solvents and at lower temperatures between N-propynoyl camphorsultams and bicyclic alkenes.

A novel ring-opening mode of cyclopropanated 7-oxa­benzonorbornadiene under acid catalysis has been discovered, providing various 2-(alkoxymethyl)naphthalenes through the use of alcohol nucleophiles. The reaction was most effective with catalytic p-TsOH∙H2O in methanol, offering yields up to 91%. The compatibility of secondary and tertiary alcohols, as well as functionalized substrates was also demonstrated.

Palladium-catalyzed ring-opening reactions of C1-substituted oxabenzonorbornadienes with aryl iodides are studied.

The ester (I), readily available from D-ribose, is transformed under optimized conditions to the stereodefined cyclopentene intermediate (II).

1,3-Dipolar cycloadditions of 7-oxa- and 7-azabenzonorbornadienes with in situ generated nitrile oxides afford exclusively exo-cycloadducts.

Both symmetrical and unsymmetrical 7-oxabenzonorbornadienes are cyclopropanated using gaseous diazomethane in the presence of a Pd catalyst.

Novel approach for the preparation of 2-methyl-1,2-dihydronaphthalen-1-ols via organocopper-mediated ring-opening reaction of cyclopropanated 7-oxabenzonorbornadiene is reported.

A novel one-pot two-step approach allows the conversion of iodo substituted azide (I) into the target amine (II) on multigram scale.

Strongly electron donating or withdrawing substituents are not tolerated in the C2-position.

Indolizidine alkaloids constitute a very important class of natural products. These metabolites derived from lysine can be isolated from diverse sources, like fungi, bacteria, higher plants, invertebrates, and vertebrates. Their core structure is characterized by fused sixand five-membered rings, with a bridgehead nitrogen atom, and is found in 25–30% of all naturally occurring alkaloids. The most important types of indolizidines are plant-derived polyhydroxylated indolizidines, like swainsonine and castanospermine, which are glycosidase inhibitors with activity against HIV, as well as alkylindolizidines, like monomorine (3), which is isolated from ants (Monomorium pharaonis) and from the skin of amphibians (Melanophryniscus stelzneri), and is believed to serve in their defense against predators (Scheme 1).

Three component reaction of aromatic amines, triethyl orthoformate, and tosylamidoxime affords 1,2,4-triazoles.

The first completely selective C3 C–H arylation of benzo[b]thiophenes is reported, demonstrating previously unexploited reactivity of palladium. Benzo[b]thiophenes are coupled with readily available aryl chlorides using a ligand-free, dual catalytic system of heterogeneous Pd/C and CuCl. The reaction is operationally simple and insensitive to air and moisture, and it provides valuable products with complete selectivity. Significant investigations into the nature of the active catalytic species and mechanistic considerations are discussed.

Cost-efficient production of sustainably-derived biochemicals and biofuels is a critical goal of modern biotechnology. The current predominant biotransformation method is mainly based on microbial fermentation, but this system suffers from a mismatch of engineering and cellular objectives, appropriates a significant fraction of substrate/energy sources for self-replication, and poses significant scaling challenges. Cell-free biosystems for biomanufacturing (CFB2)—complex, cell-free systems that catalyze the conversion of renewable substrates to a variety of products—are emerging as an alternative to fermentation. Within this burgeoning field, a new application is the production of low-value and high-impact biocommodities by CFB2. In this subset, synthetic enzymatic networks are capable of producing numerous desired biocommodities, with the advantages of higher product yields, faster reaction rates, and reduced interference from toxic compounds, among others. In this review, CFB2, with an emphasis on biocommodities production, is compared with microbial fermentation; current applications are presented, illustrating some of the advantages of the system; and remaining challenges are discussed with the path forward for each.

Retention or inversion of alkene geometry during bromination depend on both ring size and steric relations in the substrate.

Oxabicyclic alkenes are valuable synthetic intermediates as they can serve as a general template to create highly substituted ring systems.[ 1 ] For instance, metal-catalyzed ring opening of these ...

Amongst the areas of supramolecular chemistry, low molecular weight gelators (supramolecular gels) have been considered to be one of the most interesting soft and smart materials due to their ability to construct polymeric structures from small molecules through non-covalent interactions. Recently, metal centres have been incorporated into organic-based gelators that can integrate the interesting and unique properties of metal complexes into gelator molecules that can hardly be achieved by pure organic compounds. In this review, we will give a summary of the recent developments on metallogels and their interesting properties originating from the metal centres.

The title compounds, which are of interest as precursors of highly substituted ring systems, can be directly prepared by Diels—Alder reaction of benzyne with 2-substituted furans.

Circular proteins, once thought to be rare, are now commonly found in plants. Their chemical synthesis, once thought to be difficult, is now readily achievable. The enabling methodology is largely due to the advances in entropic chemical ligation to overcome the entropy barrier in coupling the N- and C-terminal ends of large peptide segments for either intermolecular ligation or intramolecular ligation in end-to-end cyclization. Key elements of an entropic chemical ligation consist of a chemoselective capture step merging the N and C termini as a covalently linked O/S-ester intermediate to permit the subsequent step of an intramolecular O/S-N acyl shift to form an amide. Many ligation methods exploit the supernucleophilicity of a thiol side chain at the N terminus for the capture reaction, which makes cysteine-rich peptides ideal candidates for the entropy-driven macrocyclization. Advances in desulfurization and modification of the thiol-containing amino acids at the ligation sites to other amino acids add extra dimensions to the entropy-driven ligation methods. This minireview describes recent advances of entropy-driven ligation to prepare circular proteins with or without a cysteinyl side chain.

The desired allene products are obtained in good to excellent yields in the presence of MeOH including an asymmetric version for (IIIa).

Both diastereomers can be obtained stereoselectively starting from chiral substrates and using the enantiomeric catalysts (I).

Aryl 2-furans (III) are prepared by palladium-catalyzed Suzuki coupling reaction, whereas alkyl 2-furans (V) are more efficiently prepared by iron-catalyzed coupling reaction.

The development and application of chemical technologies enabling direct analysis of enzyme activity in living systems has undergone explosive growth in recent years. Activity-based protein profiling (ABPP) is a key constituent of this broad field, and is among the most powerful and mature chemical proteomic technologies. This tutorial review introduces the essential features of ABPP and the design and application of activity-based probes (ABPs) from drug target elucidation and in vivo visualisation of enzyme activity to comprehensive profiling of the catalytic content of living systems, and the discovery of new biological pathways.

involving the Pd-catalyzed regioselective ethylation of dibromide (I), Diels—Alder cycloaddition of the resulting pyrone (III), and a subsequent lactone opening with Me-ONa as the key steps