Acceleration effect of allylic hydroxy group on ring-closing enyne metathesis of terminal alkynes: scope and application to the synthesis of isofagomine

An interesting allylic substituent effect on ring-closing enyne metathesis has been found. An allylic hydroxy group on enyne substrates accelerates ring-closing enyne metathesis of terminal alkynes. The reaction proceeds smoothly without ethylene atmosphere and/or more reactive newer generation Ru-carbene catalysts, which are generally necessary to promote the reaction. This efficient reaction was applied to the synthesis of isofagomine.     

Synthesis and structure of novel cyclonucleoside analogues of uridine

Novel cyclonucleoside analogues of uridine having pentylene and hexylene linker between the 5′-O and 3-N positions (thereby generating a 13- and 14-membered ring, respectively) were synthesized from uridine via ring-closing metathesis. An example of cyclic dinucleosides having two butylene linkers between the 5′-O and 3-N positions (24-membered ring) was synthesized from uridine via tandem cross-metathesis and ring-closing metathesis.     

Self-supported oligomeric Grubbs/Hoveyda-type Ru-carbene complexes for ring-closing metathesis

On the basis of the release-return metathesis mechanism, self-supported oligomeric Grubbs/Hoveyda-type Ru-carbene complexes have been designed and synthesized as a new type of recoverable catalyst for ring-closing metathesis. The catalytic activities of the self-supported oligomeric Ru-carbene complex in ring-closing metathesis are comparable to those of their homogeneous counterpart as they work homogeneously and are recovered heterogeneously.     

Diastereoselective ring-closing metathesis: synthesis of P-stereogenic phosphinates from prochiral phosphinic acid derivatives

[reaction: see text] The preparation of phosphorus-containing trienes featuring two diastereotopic vinyl moieties followed by a diastereoselective ring-closing metathesis is described. This methodology allowed for the synthesis of novel highly functionalized P-stereogenic heterocycles featuring both an exo- and an endocyclic double bond. An investigation into the factors influencing the diastereochemical outcome of the ring-closing metathesis is also presented, revealing that the geometry of the double bonds conjugated to phosphorus is important and that 1,3-stereoinduction is superior to 1,4-stereoinduction for these reactions.     

Tandem cyclopropanation/ring-closing metathesis of dienynes

Certain dienynes give cyclorearrangement by tandem cyclopropanation/ring-closing alkene metathesis, triggered by either a ruthenium carbene or noncarbene ruthenium(II) precatalyst. The process represents a variation of enyne metathesis where presumed cyclopropyl carbene intermediates undergo a consecutive ring-closing metathesis. A mechanistic proposal is offered, and sequential use of catalysts provided a tandem ring-closing enyne/alkene metathesis product.     

Diversity-oriented approach to biologically relevant molecular frameworks starting with beta-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.     

Regio- and stereoselective enyne cross metathesis of silylated internal alkynes

Cross metathesis between silylalkynes and various functionalized alkenes catalyzed by Grubbs carbene complex produced, in most cases, single regio- and stereoisomers of the resultant 1,3-dienes. Polar heteroatom substituents at the propargylic site are important for high reactivity and selectivity. An important mechanistic insight regarding the initiation event and the key propagating alkylidene in this reaction was obtained by employing a tandem cross metathesis ring-closing metathesis between a terminal alkene and a silylated alkyne possessing an alkene tether.     

First total synthesis of herbarumin III

An asymmetric 10-step total synthesis of herbarumin III in 24% overall yield is described using ring-closing metathesis as the key step.     

Metathetic approach to naphthoxepin and spirocyclic molecular frameworks

An efficient method for the synthesis of naphthoxepin and spirocyclic skeletons starting from β-naphthol has been developed. The Claisen rearrangement and the ring-closing metathesis reaction are used as key steps for their assembly.     

Stereoselective construction of the tetracyclic core of Cryptotrione

An efficient stereoselective approach to the tetracyclic core of Cryptotrione, involving an asymmetric Michael addition, ring-closing metathesis, and subsequent cyclopropanation, is described.     

Microwave-assisted ruthenium-catalyzed olefin metathesis under solvent-free conditions

An efficient method for ring-closing metathesis under solvent-free conditions and by microwave activation was established. Non-thermal microwave specific effects were evident.     

A ring-closing metathesis approach to secosteroidal macrocycles

An efficient synthesis of secosteroidal macrocycles has been achieved via an oxidative ring-expansion/ring-opening sequence and a ring-closing metathesis reaction as the key steps.     

Allylic alkylation and ring-closing metathesis in sequence: a successful cohabitation of Pd and Ru

An allylic alkylation/ring-closing metathesis domino catalytic process, wherein a palladium and a ruthenium catalyst are concomitantly present in the reaction mixture from the outset of the reaction, is developed. Evidence for Grubbs' catalysts activity in allylic alkylation is also reported.     

Expedient Route to the functionalized calyciphylline A-type skeleton via a Michael addition-RCM strategy

An efficient, robust, and scalable strategy to access the functionalized core of calyciphylline A-type alkaloids has been developed starting from commercially available 3-methylanisole. Key features of this approach are an intramolecular Michael addition/allylation sequence and a ring-closing metathesis step.     

An imine addition/ring-closing metathesis approach to the spirocyclic core of halichlorine and pinnaic acid

[reaction: see text] An approach to the spirocyclic core of halichlorine and pinnaic acid has been designed around an imine allylation/ring-closing metathesis sequence. This sequence has been used to generate several azabicylo[n.5] model systems. A newly reported metathesis catalyst was show to be highly effective for cyclization of these systems.     

The synthesis of 12-membered macrocycles containing a C1–C8 alkene unit via ring-closing metathesis

Model cross and ring-closing metathesis strategies toward the C1–C8-linear carbon skeleton are presented. The introduction of a four-atom tether enables the formation of 12-membered rings in good-to-excellent yields and stereoselectivity. Furthermore, the study revealed that the cross-metathesis approach and the formation of medium ring sizes via ring-closing metathesis are much less favorable.     

A fine-tuned molybdenum hexacarbonyl/phenol initiator for alkyne metathesis

A new, highly potent activator for molybdenum hexacarbonyl and 2-fluorophenol is described. An "instant"catalyst formed in situ from molybdenum hexacarbonyl and 2-fluorophenol shows high activity for cross- and ring-closing alkyne metathesis reaction. The use of 2-fluorophenol can be combined with other activation methods to allow alkyne metathesis at relatively low temperature (80 degrees C).     

Stereoselective synthesis of (−)- and (+)-pentenomycins using RCM

An efficient synthesis of enantiopure (−)- and (+)-pentenomycins are described by reductive iodo elimination and ring-closing metathesis (RCM), as the key steps. The first synthesis of the unnatural (+)-isomer is described.     

Well-Defined Alkyne Metathesis Catalysts: Developments and Recent Applications

Although alkyne metathesis has been known for 50 years, rapid progress in this field has mostly occurred during the last two decades. In this article, the development of several highly efficient and thoroughly studied alkyne metathesis catalysts is reviewed, which includes novel well-defined, in situ formed and heterogeneous systems. Various alkyne metathesis methodologies, including alkyne cross-metathesis (ACM), ring-closing alkyne metathesis (RCAM), cyclooligomerization, acyclic diyne metathesis polymerization (ADIMET), and ring-opening alkyne metathesis polymerization (ROAMP), are presented, and their application in natural product synthesis, materials science as well as supramolecular and polymer chemistry is discussed. Recent progress in the metathesis of diynes is also summarized, which gave rise to new methods such as ring-closing diyne metathesis (RCDM) and diyne cross-metathesis (DYCM).     

Oligometallic template strategy for ring-closing olefin metathesis: highly cis- and trans-selective synthesis of a 32-membered macrocyclic tetraoxime

An oligometallic template effect was observed on the cis/trans selectivity of a 32-membered macrocyclic tetraoxime in ring-closing olefin metathesis of an acyclic diallyl derivative H4L; the metathesis of heterotrinuclear complex LZn2M (M=Ca2+, La3+) afforded the cis isomer, whereas uncomplexed H4L gave the trans isomer.