Combination Of Ring-closing Metathesis Research Articles

Synthesis and Cytotoxicity Evaluation of Betulin Cycloolefin Derivatives by Ruthenium-Catalyzed Ring-Closing Metathesis.

The combination of ring-closing metathesis with betulin enables the design and synthesis of novel biomolecules representing a library of triterpenoid derivatives for potential pharmacological research. In this work, cyclic olefin betulin derivatives were attempted to be prepared by the combination of ring-closing metathesis with betulin. Dicyclohexyl carbodiimide coupling reaction allowed the transformation of betulin into two types of linear olefin derivatives that have different methylene spacer lengths between the olefin and ester groups. Subsequently, betulin-based cycloolefins were synthesized by ring-closing metathesis using Grubbs first-generation catalyst. The influence of different parameters including solvents, temperature, catalysts, and catalyst loading on ring-closing metathesis was investigated. Cytotoxicity results indicated that these betulin-based olefin derivatives, derived from renewable bioresources, have potential applications in the biomedical field.

Total Synthesis of Aigialomycin D Using a Ramberg−Bäcklund/RCM Strategy

The bioactive resorcylic acid lactone aigialomycin D (1) has been synthesized by a novel combination of ring-closing metathesis (RCM) and Ramberg-Bäcklund reactions. This synthetic strategy enables the C1'-C2' alkene to be masked as a sulfone during formation of the macrocycle by ring closing metathesis at the C7'-C8' olefin, thus avoiding competing formation of a cyclohexene. A subsequent Ramberg-Bäcklund reaction efficiently produces the C1'-C2' E-alkene. This combined RCM/Ramberg-Bäcklund reaction strategy should be widely applicable to the synthesis of macrocyclic dienes.

Combination of RCM and the Pauson–Khand Reaction: One‐Step Synthesis of Tricyclic Structures

AbstractThe combination of ring‐closing metathesis (RCM) followed by an intramolecular Pauson–Khand reaction gives direct entry to tricyclic compounds. The RCM was carried out on a hexacarbonylcobalt‐complexed alkyne, this complex acting as a protecting group against enyne metathesis. The procedure was studied for dienynes containing heteroatoms and allows the building of [6,5,5] and [7,5,5] tricyclic systems. The feasibility of the process depends strongly on the nature of the substrate.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Intramolecular silicon-assisted cross-coupling reactions: general synthesis of medium-sized rings containing a 1,3-cis-cis diene unit.

The combination of ring-closing metathesis and Pd-catalyzed, silicon-assisted intramolecular cross-coupling has been developed to provide an effective and powerful method for construction of medium-sized rings with an internal 1,3-cis-cis diene unit. Allylic alcohols bearing a Z-iodoalkenyl tether can be silylated with chlorodimethylvinylsilane and subjected to Mo-catalyzed ring-closing metathesis to form unsaturated siloxanes. Activation of the siloxane with tetrabutylammonium fluoride in the presence of [allylPdCl](2) leads to high yielding ring-closing reactions to form 9-, 10-, 11- and 12-membered rings. Extension to the synthesis of 9-membered ring unsaturated ethers has also been accomplished. Noteworthy features of this process include: (1) a highly stereospecific intramolecular coupling process, (2) flexible positioning of the hydroxy group, and (3) potential extension to other medium-sized carbocycles and heterocycles.

ChemInform Abstract: Synthesis of 2-Substituted Chromenes via Ring-Closing Metathesis and Stable 1-Benzopyrylium Ions.

Abstract 2-Substituted chromenes were obtained via combination of ring-closing metathesis of allylic acetals to the corresponding cyclic acetals, followed by Lewis acid-mediated functionalization of the resulting stable 1-benzopyrylium ion with suitable nucleophiles.