Ring-closing Enyne Metathesis Research Articles

Synthesis of Allocolchicines Using Sequential Ring-Closing Enyne Metathesis−Diels−Alder Reactions

New allocolchinoids having functionality in the C ring at position C10 or C11 have been synthesized using the enyne ring-closing metathesis (RCM) reaction for construction of the seven-membered ring and a Diels-Alder-aromatization sequence for the elaboration of the aromatic ring C. [reaction: see text].

Ring closing enyne metathesis: A powerful tool for the synthesis of heterocycles

The ring closing metathesis (RCM) is a powerful method in organic synthesis for the preparation of cyclic compounds by formation of new carbon-carbon bonds. In the past years a particular subclass of the RCM, the ring closing enyne metathesis (RCEYM), has attracted attention due to its synthetic potential in the generation of ring structures with 1,3-diene moieties, which can subsequently be further functionalised. In this tutorial review mechanistic considerations will be described and the synthetic power of this useful and attractive carbon-carbon bond forming reaction will be illustrated by recent examples of RCEYM applications in the preparation of heterocyclic compounds.

Enyne Metathesis–Oxidation Sequence for the Synthesis of 2‐Phosphono Pyrroles: Proof of the “Yne‐then‐Ene” Pathway

A new tandem reaction sequence has been developed for the synthesis of 2-phosphono pyrroles. The sequence consists of ring-closing enyne metathesis of a substituted aminophosphonate, containing a terminal alkyne and an internal alkene, in combination with in situ oxidation of the produced 3-pyrrolines using tetrachloroquinone. By analyzing the formation of the end and certain byproducts, taking into account the difference in reactivity of different substrates and carefully studying spectroscopic data, it was found that the reaction proceeds by means of the "yne-then-ene" pathway. During the initiation phase, a new ruthenium carbene is formed which continues the propagation cycle.

Synthesis of Thiepin-annulated Pyrone and Coumarin Heterocycles by Grubbs’ Second Generation Catalyst Mediated Enyne Metathesis

Abstract Synthesis of thiepin-annulated pyrone and coumarin derivatives has been achieved by the ring-closing enyne metathesis using the second generation Grubbs’ catalyst under a nitrogen atmosphere.

Enyne Ring‐Closing Metathesis on Heteroaromatic Cations.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Diversity‐Oriented Approach to Biologically Relevant Molecular Frameworks Starting with β‐Naphthol and Using the Claisen Rearrangement and Olefin Metathesis as Key Steps

A diversity-oriented approach for the synthesis of various structurally different molecular frameworks from readily accessible and common precursors is described. A Claisen rearrangement followed by ring-closing metathesis or ethylene-promoted ring-closing enyne metathesis has been utilized as the key synthetic transformation to generate naphthoxepine derivatives. The ring-closing metathesis approach has also been used to generate spirocyclic compounds and the pleiadene framework.

Enantioselective Total Synthesis of (−)‐Acylfulvene and (−)‐Irofulven

Antitumor agents (−)-acylfulvene and (−)-irofulven are prepared in an approach that employs the powerful enyne ring-closing metathesis reaction to secure the spiro-bicyclic AB rings. Other key features of this synthesis include an efficient aldol-based introduction of the stereocenter at C2, a diazene-mediated reductive allylic transposition, and a ring-closing metathesis/oxidation sequence.

Enantioselective Total Synthesis of (−)‐Acylfulvene and (−)‐Irofulven

We report our full account of the enantioselective total synthesis of (-)-acylfulvene (1) and (-)-irofulven (2), which features metathesis reactions for the rapid assembly of the molecular framework of these antitumor agents. We discuss (1) the application of an Evans Cu-catalyzed aldol addition reaction using a strained cyclopropyl ketenethioacetal, (2) an efficient enyne ring-closing metathesis cascade reaction in a challenging setting, (3) the reagent IPNBSH for a late-stage reductive allylic transposition reaction, and (4) the final RCM/dehydrogenation sequence for the formation of (-)-acylfulvene (1) and (-)-irofulven (2).

Oxepin- and Spiro-Annulation of 2-Pyridone in Conjunction with Claisen Rearrangement and Ruthenium Carbene Complex Mediated Enyne Metathesis (SUPPORTING DATA)

A direct synthesis of substituted oxepin and spiroheterocycles has been achieved from substrates derived from 4-hydroxy-1,6-dimethyl pyridine-2-ones (1) by combining Claisen rearrangement and ring closing enyne metathesis. The RCEM proceeded smoothly under nitrogen atmosphere at room temperature in the presence of well-defined ruthenium catalyst A (10 mol%).

Synthesis of Polycyclic Coumarin Derivatives by Combined Claisen Rearrangement, Ring-closing Metathesis, and Diels–Alder Reaction

Abstract A new route to several hitherto unknown linearly and angularly architectured polycyclic coumarin derivatives has been developed involving tandem applications of three atom economic processes viz. Claisen rearrangement, ring-closing enyne metathesis, and Diels–Alder reactions.

Group‐Selective Ring‐Closing Enyne Metathesis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Tandem Claisen rearrangement and ruthenium catalyzed enyne bond reorganization as a route to the synthesis of tricyclic 1,8-naphthyridinones

A novel procedure for the synthesis of substituted 1,8-naphthyridinones via tandem Claisen rearrangement and ring-closing enyne metathesis is reported.

Stereoselective Synthesis of Tricyclic Pyranoxepin Derivatives by Ruthenium-Catalyzed Enyne Metathesis/Diels-Alder Reaction

Synthesis of tricyclic oxepin-annulated pyrone derivatives has been achieved by the ring-closing enyne metathesis using the first-generation Grubbs' catalyst under a nitrogen atmosphere. The Diels-Alder reaction of these cyclized products with the dienophile proceeded smoothly to afford the tricyclic compounds in excellent yield.

Enyne ring-closing metathesis on heteroaromatic cations

Cationic heteroaromatic enynes have been employed as substrates in enyne ring-closing metathesis, under an atmosphere of ethylene and using the Hoveyda-Grubbs catalyst, for the first time; the reaction affords new 1-vinyl- and 2-vinyl-substituted 3,4-dihydroquinolizinium salts, useful precursors for biologically relevant cations based on the quinolinizium system.

Ring-Closing Metathesis of Heteroatom-Substituted Dienes

The ring-closing metathesis (RCM) of dienes that contain at least one participating heteroatom-substituted olefin is reviewed (olefins substituted with O, N, S, P, Si, B, and halogen atoms will be considered). Efforts have been made to include as many relevant examples of RCM of heteroatom-substituted dienes as possible, but due to the increasing volume of research in this area, an exhaustive coverage is not intended. Attention has focussed on diene RCM reactions catalysed by ruthenium and molybdenum alkylidene complexes, although a brief discussion of some ring-closing reactions of titanium alkylidene species is provided. Other metathesis reactions such as enyne RCM, cross-metathesis and ROMP are not included.

Preparation of Alkenyl Cyclopropanes through a Ruthenium-Catalyzed Tandem Enyne Metathesis−Cyclopropanation Sequence

Acyclic enynes undergo a tandem enyne metathesis/cyclopropanation sequence in the presence of Grubbs' 1st generation metathesis catalyst and diazo compounds. In practice, the acyclic substrates in the presence of the ruthenium alkylidene first undergo a ring-closing enyne metathesis to generate cyclic 1,3-dienes; then upon addition of a diazo compound, these products are cyclopropanated selectively at the more accessible olefin. Overall, the reaction sequence converts acyclic enynes into vinyl cyclopropanes in single operation through two unique ruthenium-catalyzed transformations.

Rate Enhancement by Ethylene in the Ru‐Catalyzed Ring‐Closing Metathesis of Enynes: Evidence for an “Ene‐then‐Yne” Pathway that Diverts through a Second Catalytic Cycle

Mixing it: A dual-substrate/dual isotopic labeling strategy has shown that the accelerating effect of ethylene in intermolecular ring-closing metathesis of enynes is best explained by an ene-then-yne mechanism rather than the commonly proposed yne-then-ene mechanism (see picture).

Asymmetric Synthesis of (‐)‐Dihydroxanthatin by the Stereoselective Oshima—Utimoto Reaction.

The catalytic stereoselective Oshima−Utimoto reaction is useful for the construction of five-membered oxacycles from simple starting materials and was employed for the preparation of the lactone group in the asymmetric synthesis of (−)-11α,13-dihydroxanthatin. Completion of the synthesis is facilitated by ring-closing enyne metathesis and alkene cross metathesis reactions.

Synthesis and determination of absolute configuration of tetracetate 4a-carba- d-xylofuranoside

The synthesis of carbasugar analogue tetracetate 4a-carba- d-xylofuranoside ( 1 ) was reported. The new route involved the conversion of d-(−)-tartatic acid into an enyne compound, which was then cyclized via a key ring-closing enyne metathesis to form the key intermediate 1-vinyl cyclopentene 9 , which was then stereoselectively converted to our target. The absolute configuration of the enyne was determined by modified Mosher's method, while that of tetracetate 4a-carba- d-xylofuranoside by ROSEY spectroscopy and γ- gauche effect.

Group‐Selective Ring‐Closing Enyne Metathesis

The ring-closing metathesis (RCM) of dienynes represents a powerful methodology for the construction of mono- and bicyclic systems containing 1,3-diene functionality. Despite its synthetic potential, the utility of dienyne RCM is significantly reduced due to poor group selectivity. To circumvent this shortcoming, several strategies utilizing steric hindrance, electronic variation, relay metathesis and ring-closure kinetics have been implemented to exert control over the reaction pathways. This article highlights a variety of methods to achieve group-selective enyne RCM of dienynes.