New acetogenin peroxides from the Indian sponge Acarnus bicladotylota

Indium(III)-Catalyzed Haloalkynylation Reaction of Alkynes

Green chemistry strives for sustainability at the molecular level and is gaining increasing relevance in the development of chemical reactions. The haloalkynylation reaction is a highly atom-economical C-C coupling reaction that was previously only achieved using transition metal catalysts. It enables the introduction of an alkyne unit and a halogen atom into the target molecule. Herein, we present a haloalkynylation reaction catalyzed by indium(III) halides. The use of indium(III) bromide as a catalyst leads exclusively to the cis addition products with yields up to 86 %. In addition, iodoacetylenes can be applied for the first time for the haloalkynylation reaction of internal alkynes which is an important step forward in the development of industrially relevant and sustainable catalysts. In contrast to gold catalysis, which proceeds via a similar mechanism, the use of alkyl-substituted haloacetylenes as reagents is also possible. Based on 13C labeling experiments and quantum chemical calculations, we postulate two possible mechanisms for the indium(III)-catalyzed haloalkynylation reactions.

trans-Hydroalkynylation of Internal 1,3-Enynes Enabled by Cooperative Catalysis

A cooperative catalyst system involving a Pd(0)/Senphos complex, tris(pentafluorophenyl)borane, copper bromide, and an amine base, is demonstrated to catalyze trans-hydroalkynylation of internal 1,3-enynes. For the first time, a Lewis acid catalyst is shown to promote the reaction involving the emerging outer-sphere oxidative reaction step. The resulting cross-conjugated dieneynes are versatile synthons for organic synthesis, and their characterization reveals distinct photophysical properties depending on the positioning of the donor/acceptor substituents along the conjugation path.

Cascade Multicomponent Assemblies Involving 1,3-Enynes via Auto-Tandem Palladium Catalysis

Here we report a three-component auto-tandem reaction of 1,3-enyne-tethered carbonyls, organoboronic reagents, and suitable nucleophiles catalyzed by palladium, proceeding through consecutive intramolecular vinylogous addition, Suzuki coupling, and allylic alkylation. This process exhibited high chemo- and regioselectivity with 1,3,4-trifunctionalization of the 1,3-enyne motif, and a wide range of 2H-chromenes, 1,2-dihydroquinolines, benzo[b]oxepines, 1,7-annulated indoles, and other frameworks were efficiently constructed in fair to good yields and E/Z selectivity.

Alkynyl-induced construction of stereodefined polysubstituted conjugated enynes via Pd-catalyzed allylic arylations

The alkynyl-induced construction of polysubstituted conjugated enynes with exclusive (Z)-configurations via Pd-catalyzed allylic arylations is described.

Synthesis of 2-acetal-1,3-enynes by Sonogashira reaction of bromovinyl acetals with alkynes: application to the formal synthesis of a glucagon antagonist

The preparation of functionalized 1,3-enynes bearing an acetal moiety at the 2-position has been studied through Sonogashira reaction of bromovinyl acetals with various alkyl- and aryl-substituted terminal alkynes.

Access to Z-Selective 1,3-Enynes via Ni-Catalyzed Intermolecular Cross-Alkylalkynylation of Terminal Alkynes

Access to 1,3-conjugated enynes with defined stereoselectivity is highly desirable and challenging. Herein, we report a facile synthesis of stereodefined 1,3-conjugated enynes via Ni-catalyzed intermolecular cross-alkylalkynylation of alkynes with unsaturated carbonyl compounds and alkynes or alkynyl silicates. The operational simple protocol proceeds at room temperature and tolerates a wide range of functional groups, providing an attractive alternative to carbonyl-tethered trisubstituted conjugated 1,3-enynes from easily accessible starting materials.

Electro-alkynylation: Intramolecular Rearrangement of Trialkynylorganoborates for Chemoselective C(sp2)-C(sp) Bond Formation

An alternative and complementary transformation for the synthesis of aryl- and heteroaryl-substituted alkynes is presented that relies on a chemoselective electrocoupling process. Tetraorganoborate substrates were logically designed and simply accessed by transmetalations using readily or commercially available organotrifluoroborate salts.

Copper-catalyzed regio- and stereoselective fluorocarboalkynylation of alkynes

It is attractive to establish an efficient and practical platform affording functional compounds using readily available feedstocks as starting materials under mild conditions.

Palladium-catalyzed decarboxylative gem-selective addition of alkynoic acids to terminal alkynes

Alkynoic acids added to terminal alkynes to give gem-1,3-enynes with high selectivity and good yields. In addition, the reaction of alkynoic acids with propiolic acid provided the corresponding gem-1,3-enynes via double decarboxylation.

Cobalt-Catalyzed E-Selective Cross-Dimerization of Terminal Alkynes: A Mechanism Involving Cobalt(0/II) Redox Cycles

A highly E-selective cross-dimerization of terminal alkynes with either terminal silylacetylenes, tert-butylacetylene, or 1-trimethylsilyloxy-1,1-diphenyl-2-propyne in the presence of a dichlorocobalt(II) complex bearing a sterically demanding 2,9-bis(2,4,6-triisopropylphenyl)-1,10-phenanthroline, activated with two equivalents of EtMgBr, gives a variety of (E)-1,3-enynes. A well-characterized diolefin/cobalt(0) complex, with divinyltetramethyldisiloxane, acted as a catalytically active species without any activation, clearly indicating that a cobalt(0) species is involved in the catalytic cycle.

Ni/Cu-Catalyzed Decarboxylative Addition of Alkynoic Acids to Terminal Alkynes for the Synthesis of gem-1,3-Enynes

The synthesis of gem-1,3-enynes via Ni/Cu-catalyzed decarboxylative addition of alkynoic acids to terminal alkynes has been developed. It was found that the decarboxylation of an alkynoic acid led predominantly to gem-1,3-enynes instead of 1,3-diynes, which have been known to be formed through the coupling of terminal alkynes. A variety of gem-1,3-enynes were obtained in good yields. This catalytic system exhibited excellent regioselectivity and high functional group tolerance.

Discovery of chitin in skeletons of non-verongiid Red Sea demosponges

Marine demosponges (Porifera: Demospongiae) are recognized as first metazoans which have developed over millions of years of evolution effective survival strategies based on unique metabolic pathways to produce both biologically active secondary metabolites and biopolymer-based stiff skeletons with 3D architecture. Up to date, among marine demosponges, only representatives of the Verongiida order have been known to synthetize biologically active substances as well as skeletons made of structural polysaccharide chitin. This work, to our knowledge, demonstrates for the first time that chitin is an important structural component within skeletons of non-verongiid demosponges Acarnus wolffgangi and Echinoclathria gibbosa collected in the Red Sea. Calcofluor white staining, FTIR and Raman analysis, ESI-MS, SEM, and fluorescence microscopy as well as a chitinase digestion assay were applied in order to confirm, with strong evidence, the finding of α-chitin in the skeleton of both species. We suggest that, the finding of chitin within these representatives of Poecilosclerida order is a promising step in the evaluation of these sponges as novel renewable sources for both biologically active metabolites and chitin, which are of prospective application for pharmacology and biomedicine.

Synthesis of a 1,3-Bridged Macrobicyclic Enyne via Chemoselective Cycloisomerization Using Palladium-Catalyzed Alkyne-Alkyne Coupling

A unique intramolecular Pd-catalyzed alkyne-alkyne coupling is presented. This transformation generates a strained, 1,3-bridged, macrocyclic enyne. The process was readily executed on gram scale, and the structure of the product was elucidated via X-ray crystallographic analysis. A mechanistic rationale for the observed chemoselectivity is provided.

Transition metal-catalyzed couplings of alkynes to 1,3-enynes: modern methods and synthetic applications

The metal-catalyzed coupling of alkynes is a powerful method for the preparation of 1,3-enynes, compounds that are of broad interest in organic synthesis. Numerous strategies have been developed for the homo- and cross coupling of alkynes to enynes via transition metal catalysis. In such reactions, a major issue is the control of regio-, stereo-, and, where applicable, chemoselectivity. Herein, we highlight prominent methods for the selective synthesis of these valuable compounds. Further, we illustrate the utility of these processes through specific examples of their application in carbocycle, heterocycle, and natural product syntheses.

One-pot synthesis of 1,3-enynes with a CF3 group on the terminal sp2 carbon by an oxidative Sonogashira cross-coupling reaction

One-pot synthesis of 1,3-enynes with a CF₃ group on the terminal sp² carbon was achieved by an oxidative Sonogashira cross-coupling reaction with (E)-trimethyl(3,3,3-trifluoroprop-1-enyl)silane.

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

The present review describes the current status of synthetic five and six-membered cyclic peroxides such as 1,2-dioxolanes, 1,2,4-trioxolanes (ozonides), 1,2-dioxanes, 1,2-dioxenes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes. The literature from 2000 onwards is surveyed to provide an update on synthesis of cyclic peroxides. The indicated period of time is, on the whole, characterized by the development of new efficient and scale-up methods for the preparation of these cyclic compounds. It was shown that cyclic peroxides remain unchanged throughout the course of a wide range of fundamental organic reactions. Due to these properties, the molecular structures can be greatly modified to give peroxide ring-retaining products. The chemistry of cyclic peroxides has attracted considerable attention, because these compounds are used in medicine for the design of antimalarial, antihelminthic, and antitumor agents.

Peroxy natural products

This review covers the structures and biological activities of peroxy natural products from a wide variety of terrestrial fungi, higher plants, and marine organisms. Syntheses that confirm or revise structures or stereochemistries have also been included, and 406 references are cited.

Highly enantioselective reduction of 4-(trimethylsilyl)-3-butyn-2-one to enantiopure (R)-4-(trimethylsilyl)-3-butyn-2-ol using a novel strain Acetobacter sp. CCTCC M209061

The biocatalytic reduction of 4-(trimethylsilyl)-3-butyn-2-one to enantiopure (R)-4-(trimethylsilyl)-3-butyn-2-ol was successfully conducted with high enantioselectivity using immobilized whole cells of a novel strain Acetobacter sp. CCTCC M209061, newly isolated from kefir. Compared with other microorganisms that were investigated, Acetobacter sp. CCTCC M209061 was shown to be more effective for the bioreduction reaction, and afforded much higher yield and product enantiomeric excess (e.e.). The optimal buffer pH, co-substrate concentration, reaction temperature, substrate concentration and shaking rate were 5.0, 130.6 mM, 30 degrees C, 6.0 mM and 180 r/min, respectively. Under the optimized conditions, the maximum yield and the product e.e. were 71% and >99%, respectively, which are much higher than those reported previously. Additionally, the established biocatalytic system proved to be efficient for the bioreduction of acetyltrimethylsilane to (R)-1-trimethylsilylethanol with excellent yield and product e.e. The immobilized cells manifested a good operational stability under the above reaction conditions since they retained 70% of their catalytic activity after ten cycles of use.

Cobalt-catalyzed cross-coupling of alkynyl Grignard reagents with alkenyl triflates

Alkenyl triflates in combination with Co(acac)(3) as a catalyst were found to be excellent coupling partners of alkynyl Grignard reagents, where no special additives (even a phosphine ligand) but a common solvent, THF, are required to obtain variously substituted enynes.

Bioactive peroxides as potential therapeutic agents

Present review describes research on more than 280 natural anticancer agents isolated from terrestrial and marine sources and synthetic biologically active peroxides. Intensive searches for new classes of pharmacologically potent agents produced by terrestrial and marine organisms have resulted in the discovery of dozens of compounds possessing high cytotoxic, antibacterial, antimalarial, and other activities as an important source of leads for drug discovery.

Marine natural products

This review covers the literature published in 2005 for marine natural products, with 704 citations (493 for the period January to December 2005) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (812 for 2005), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Total Synthesis of Peroxyacarnoates A and D: Metal-Mediated Couplings as a Convergent Approach to Polyunsaturated Peroxides

[reaction: see text] The first syntheses of peroxyacarnoates A and D, members of a family of enyne-containing alkoxydioxanes, have been achieved on the basis of chemoselective ozonolysis within a polyunsaturated framework and Pd-mediated cross-couplings of a functionalized 1,2-dioxane.

Copper-Catalyzed Synthesis of 1,3-Enynes

[reaction: see text] We report a copper(I)-catalyzed procedure for the synthesis of 1,3-enynes. This method affords a variety of enynes in good to excellent yields. This method can tolerate a variety of functional groups, does not require the use of expensive additives, and is palladium-free.

New chemical constituents of Euphorbia quinquecostata and absolute configuration assignment by a convenient Mosher ester procedure carried out in NMR tubes

Two new compounds, an ent-isopimarane-type diterpene, 3alpha,12alpha-dihydroxy-ent-8(14),15-isopimaradien-18-al (1), and a dihydrobenzo[b]furan neolignan, (-)-trans-9-acetyl-4,9'-di-O-methyl-3'-de-O-methyldehydrodiconiferyl alcohol (2), along with five known compounds, 7,7'-dihydroxy-6,8'-bicoumarin (bicoumol) (3), 3,4-dimethoxycinnamaldehyde (4), 6-hydroxy-7-methoxycoumarin (isoscopoletin), N-butylaniline, and vanillin, have been isolated from an ethyl acetate-soluble extract of the stem wood of Euphorbiaquinquecostata. The structures of compounds 1 and 2 were elucidated on the basis of spectroscopic data interpretation, and single-crystal X-ray diffraction analysis was used to confirm the structure and relative stereochemistry of 1. The absolute configuration of 1 was established by a convenient Mosher ester procedure in which the sample was treated with MTPA chlorides in deuterated pyridine directly in NMR tubes. All isolates were evaluated for the induction of quinone reductase in Hepa1c1c7 hepatoma cells and for the inhibition of the transformation of murine epidermal JB6 cells.