Enantioselective Synthesis of 5-epi-Citreoviral Using Ruthenium-Catalyzed Asymmetric Ring-Closing Metathesis

Chiral ruthenium olefin metathesis catalysts can perform asymmetric ring-closing reactions in ≥90% ee with low catalyst loadings. To illustrate the practicality of these reactions and the products they form, an enantioselective total synthesis of 5-epi-citreoviral was completed by using an asymmetric ring-closing olefin metathesis reaction as a key step early in the synthesis. All of the stereocenters in the final compound were set by using the chiral center generated by asymmetric olefin metathesis

Cross Metathesis Assisted Solid-Phase Synthesis of Glycopeptoids

A solid-phase synthesis of glycopeptoids was explored through olefin cross metathesis (CM). Peptoids and sugar derivatives with appropriate olefin moieties were coupled in the presence of an olefin metathesis catalyst to afford glycopeptoids in good yields. This systematic solid-phase CM study can provide facile access to the molecular sources of glycopeptidomimetics and postchemical modifications on various molecular scaffolds

Ru-Catalyzed, cis-Selective Living Ring-Opening Metathesis Polymerization of Various Monomers, Including a Dendronized Macromonomer, and Implications to Enhanced Shear Stability

An unsaturated polymer’s cis/trans-olefin content has a significant influence on its properties. For polymers obtained by ring-opening metathesis polymerization (ROMP), the cis/trans-olefin content can be tuned by using specific catalysts. However, cis-selective ROMP has suffered from narrow monomer scope and lack of control over the polymerization (giving polymers with broad molecular weight distributions and prohibiting the synthesis of block copolymers). Herein, we report the versatile cis-selective controlled living ROMP of various endo-tricyclo[4.2.2.0^(2,5)]deca-3,9-diene and various norbornene derivatives using a fast-initiating dithiolate-chelated Ru catalyst. Polymers with cis-olefin content as high as 99% could be obtained with high molecular weight (up to M_n of 105.1 kDa) and narrow dispersity (<1.4). The living nature of the polymerization was also exploited to prepare block copolymers with high cis-olefin content for the first time. Furthermore, owing to the successful control over the stereochemistry and narrow dispersity, we could compare cis- and trans-rich polynorbornene and found the former to have enhanced resistance to shear degradation

Sprectral data for Generation of Molecular Complexity from Cyclooctatetraene Using Dienyliron and Olefin Metathesis

Spectral data used in the course of researching Generation of molecular complexity from cyclooctatetraene using dienyliron and olefin metathesis methodology . Transformation of the simple hydrocarbon cyclooctatetraene into a variety of polycyclic skeletons was achieved by sequential coordination to iron, reaction with electrophiles followed by allylated nucleophiles, decomplexation and olefin metathesis

Chelated Ruthenium Catalysts for Z-Selective Olefin Metathesis

We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands that catalyze highly Z-selective olefin metathesis. A very simple and convenient procedure for the synthesis of such catalysts has been developed. Intramolecular C–H bond activation of the NHC ligand, promoted by anion ligand substitution, forms the appropriate chelate for stereocontrolled olefin metathesis

Facile Synthesis of Effcient and Selective Ruthenium Olefin Metathesis Catalysts with Sulfonate and Phosphate Ligands

A series of novel, air-stable ruthenium NHC catalysts with sulfonate and phosphate anions have been prepared easily in one pot at high yields using commercially available precursors. The catalysts were found to be effective for ring-opening metathesis polymerization, ring-closing metathesis, and cross-metathesis. The catalysts showed higher cis-selectivity in olefin cross-metathesis reactions as compared to earlier known ruthenium-based olefin metathesis catalysts, with allylbenzene and cis-1,4-diacetoxybutene as substrates

Conformational analysis of olefin-carbene ruthenium metathesis catalysts

We settle a long-standing disagreement of DFT with experiment (both solution and gas phase) for the phosphine dissociation process in Grubbs metathesis catalysis. Our findings with the M06 functional provide further support to gas-phase experimental work, concluding that for the ring-closing metathesis of norbornene, the resting state is the alkylidene−olefin complex and the rate-determining step is the loss of norbornene as a ligand and generation of the 14-electron activated species. Comparing to recent solution NMR data on olefin−carbene Ru complexes relevant to olefin metathesis, we find that the M06 density functional leads to accurate predictions for the stability of conformers, ~0.5 kcal/mol better than is found by B3LYP. Using this methodology, we suggest that Piers and co-workers observed the cis-dichloro “down” isomer exclusively following the ring opening of acenaphthalene

Tandem ring-closing metathesis reaction with a ruthenium catalyst containing a N-heterocyclic ligand

The highly active catalyst 2 was used in tandem RCM to make molecules with various ring systems containing α,β-unsaturated carbonyl compounds

The Metallacyclopentane-Olefin Interchange Reaction

Tris(triphenylphosphine)tetramethylenenickel(II) and biscyclopentadienyltetramethylenetitanium, prepared from the reaction of a 1,4-dilithiobutane and the transition metal dihalides react with olefins to produce substituted metallacyclopentanes; the stereochemistry and substitution pattern of the metallocycles formed from propene, octa-1,7-diene, and norbornadiene has been determined

Ruthenium Olefin Metathesis Catalysts Bearing Carbohydrate-Based N-Heterocyclic Carbenes

Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy revealed the presence of Ru−C (benzylidene) rotamers at room temperature, and the rate of rotation was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to be effective at ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), cross-metathesis (CM), and asymmetric ring-opening cross-metathesis (AROCM) and showed surprising selectivity in both CM and AROCM