Allenic Ethers Research Articles

New Pyranone Derivatives and Sesquiterpenoid Isolated from the Endophytic Fungus Xylaria sp. Z184.

The fungus Xylaria sp. Z184, harvested from the leaves of Fallopia convolvulus (L.) Á. Löve, has been isolated for the first time. Chemical investigation on the methanol extract of the culture broth of the titles strain led to the discovery of three new pyranone derivatives, called fallopiaxylaresters A-C (1-3), and a new bisabolane-type sesquiterpenoid, named fallopiaxylarol A (4), along with the first complete set of spectroscopic data for the previously reported pestalotiopyrone M (5). Known pyranone derivatives (6-11), sesquiterpenoids (12-14), isocoumarin derivatives (15-17), and an aromatic allenic ether (18) were also co-isolated in this study. All new structures were elucidated by the interpretation of HRESIMS, 1D, 2D NMR spectroscopy, and quantum chemical computation approach. The in vitro antimicrobial, anti-inflammatory, and α-glucosidase-inhibitory activities of the selected compounds and the crude extract were evaluated. The extract was shown to inhibit nitric oxide (NO) production induced by lipopolysaccharide (LPS) in murine RAW264.7 macrophage cells, with an inhibition rate of 77.28 ± 0.82% at a concentration of 50 μg/mL. The compounds 5, 7, and 8 displayed weak antibacterial activity against Staphylococcus areus subsp. aureus at a concentration of 100 μM.

Synthesis of Methylenecyclobutenes by [2+2] Cycloaddition of Allene Ethers and Alkyne

AbstractMethylenecyclobutenes are useful precursors to provide other organic compounds. We report intermolecular [2+2] cycloaddition of allene ethers and alkynes at 100 °C, which gives methylenecyclobutenes in 50–60 % yields. The reaction does not require any metal catalyst and shows broad substrate scope, high regioselectivity and high stereoselectivity.

One stone three birds: Ni-catalyzed asymmetric allenylic substitution of allenic ethers, hydroalkylation of 1,3-enynes and double alkylation of enynyl ethers

The development of low-cost, earth-abundant and environmentally benign transition metal catalysts, which can catalyze multiple different types of asymmetric reactions, is an important objective in modern asymmetric catalysis. Herein we demonstrate that a chiral Ni/P-Phos catalyst achieves three types of asymmetric reactions: allenylic substitution of racemic allenic ethers, 1,4-hydroalkylation of prochiral 1,3-enynes and double alkylation of newly designed enynyl ether reagents. Three methods complement each other and produce various axially chiral allene derivatives bearing a pyrazolidine-3,5‑dione unit, which is widely present in drugs and biologically active molecules with versatile pharmacological activities.

Synthetic studies towards (±)-isopalhinine A: Preparation of the bicyclic core via Nazarov cyclization

This manuscript describes progress towards the total synthesis of (±)-isopalhinine A wherein an allene ether Nazarov cyclization gives rise to the bicyclic core.

ChemInform Abstract: Allene Ether Nazarov Cyclization

AbstractReview: [59 refs.

Allene ether Nazarov cyclization

The ease of synthesis and the exceptional reactivity of alkoxyallenes has led to their use in a large number of highly diverse applications. This Report describes their use in various versions of the allene ether Nazarov cyclization. Following a brief introduction to the Nazarov cyclization (Section 1), the oxidative cyclization of vinyl alkoxyallenes is discussed first (Section 2). Nazarov cyclizations of α-alkoxyallenyl vinyl ketones and of α-alkoxyallenyl vinyl tertiary carbinols are covered (Section 3). The discovery and the subsequent rational design of acetals that serve as chiral auxiliaries on the allene in highly enantioselective Nazarov cyclizations is explained (Section 4). Interrupted Nazarov cyclizations of alkoxyallenes that are generated in situ from the isomerization of propargyl ethers on solid supports are discussed, including the evolution of a highly diastereoselective, chiral auxiliary controlled version of the reaction. Some applications of the methodology to natural products total synthesis have been included so as to provide the reader with benchmarks with which to judge the utility of the methodology.

ChemInform Abstract: Synthesis of Silyl, Germyl, and Phosphino-Substituted Acylketenes from Pivaloylethoxyacetylene.

The reaction of pivaloylethoxyacetylene with silicon halides, which has been found to occur as a 1,4-addition, leads to allenic ethers, which readily eliminate ethyl halides and are converted to previously unknown types of ketenes—stable element-substituted acylketenes. Germanium-substituted acylketenes are also formed; however, clear evidence of 1,4-addition of germanium halides was not obtained. In the reaction between Ph2PCl and pivaloylethoxyacetylene, phosphorus (III) substituted acylketenes initially formed underwent rapid [3 + 3] cyclodimerization.

Traceless Chiral Auxiliaries for the Allene Ether Nazarov Cyclization

The key stereochemical factors that determine transfer of asymmetry from the chiral auxiliary to the cyclopentenone in the allene ether version of the Nazarov reaction have been elucidated. On the basis of the new insights into the mechanism, two highly effective chiral auxiliaries were designed and prepared.

Four new aromatic allenic ethers from the fungus Xylaria sp. No. 2508

Four new aromatic allenic ethers, (7E)-3-(4-buta-2,3-dienyloxy-3-methoxy-phenyl)-acrylic acid methyl ester (1), (7E)-3-[4-(4-buta-2,3-dienyloxy-benzyloxy)-phenyl]-acrylic acid methyl ester (2), 4-(4-buta-2,3-dienyloxy-benzyloxy)-benzoic acid methyl ester (3), (7E)-3-[4-(4-buta-2,3- dienyloxy-benzyloxy)-3-methoxy-phenyl]-acrylic acid methyl ester (4) were isolated from the fungus Xylaria sp. No. 2508. The structures of those compounds were determined by analysis of spectroscopic data, mainly 2D NMR experiments.

Total Synthesis of (±)-Terpestacin and (±)-11-epi-Terpestacin

The total synthesis of racemic terpestacin and 11-epi-terpestacin using the allene ether Nazarov reaction as the key step is described. All stereochemistry is derived from the stereogenic carbon atom that is formed during the Nazarov reaction.

Design of Chiral Auxiliaries for the Allene Ether Nazarov Cyclization

A 1,3- or a 1,4-cis axial tert-butyldimethylsilyloxy substituent on the pyranose derived chiral auxiliary for the allene ether Nazarov cyclization leads to products in high optical purity. α-Pyranose and β-pyranose derived auxiliaries lead to enantiomeric products.

Synthesis of (+)-madindoline A and (+)-madindoline B.

The allene ether version of the Nazarov cyclization was used to construct the cyclopentane dione portion of madindolines A and B. The racemic cyclopentane dione from the Nazarov cyclization was converted to an enol ether that was combined with the chiral, nonracemic hydroxyfuroindoline in a Mannich reaction. Deprotection and oxidation led to (+)-madindoline A and (+)-madindoline B. [reaction: see text].

An Improved Chiral Auxiliary for the Allene Ether Version of the Nazarov Cyclization.

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An Improved Chiral Auxiliary for the Allene Ether Version of the Nazarov Cyclization

Alpha-2-deoxy-D-glucose derived ether 14 is a superior reagent for the allene ether version of the Nazarov cyclization. Enantiomeric excesses of products derived from trisubstituted morpholino enamides varied between 85% and 93% ee. [structure: see text]

Terpestacin Core Structure. Control of Stereochemistry

[reaction: see text] The alpha-hydroxycyclopentenone core structure of terpestacin has been prepared in a model system through an allene ether Nazarov cyclization of an alkylidene-gamma-butyrolactone followed by regio- and stereoselective alkylation reactions. The stereochemistry at C15 (terpestacin numbering) has been used to control stereochemistry at C1 and at C23. The use of E-alkylidene-gamma-butyrolactones extends the scope of the cationic cyclopentannelation reaction.

Medium optimization of carbon and nitrogen sources for the production of eucalyptene A and xyloketal A from Xylaria sp. 2508 using response surface methodology

To optimize the production of novel ketal compounds and allenic ethers from a mangrove fungus Xylaria sp. 2508, optimization of the culture medium was carried out using a two-step approach. A quick identification of a suitable source of carbon and nitrogen was obtained by a simple screening experiment, which was followed by an application of response surface methodology (RSM) for further optimization design. A second order model was found to fit the eucalyptene A production. Response surface analysis revealed that the optimum values of the tested variables for the production of eucalyptene A were: glucose 2.86% (w/v), peptone 0.78% (w/v) and yeast extract 0.35% (w/v). A production of 4.89 × 10 −7 g ml −1 for eucalyptene A, which was close to the predicted response, was observed in verification experiment. The production of xyloketal A was 2.20 × 10 −7 g ml −1. In comparison to their production of basal medium, 1.53- and 1.32-fold increase had been obtained, respectively. The 3-D response surface curves implied that high yeast extract concentration repressed the growth of Xylaria sp.

Tetrasubstituted Allene Ethers; Synthesis and Use in Nazarov Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Tetrasubstituted Allene Ethers; Synthesis and Use in Nazarov Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Tetrasubstituted Allene Ethers; Synthesis and Use in Nazarov Reactions

A method for the synthesis of tetrasubstituted allene ethers is described, making use of a reverse Brook rearrangement in the key step. The allene products have been used in the Nazarov cyclization reaction.

Cationic Cyclopentanellation of Allene Ethers

AbstractFor Abstract see ChemInform Abstract in Full Text.