The effect of substituents at silicon on the cross-metathesis of trisubstituted vinylsilanes with olefins

Efficient cross-metathesis of vinylsilanes, carrying a large spectrum of different substituents at silicon, with various olefins in the presence of the first and second generation Grubbs catalyst and Hoveyda–Grubbs catalyst is described. On the basis of the results of equimolar reactions of vinylsilanes with ruthenium alkylidene complexes and experiments with deuterium-labelled reagents, a general, metallacarbene mechanism for the cross-metathesis of trisubstituted vinylsilanes with olefins has been suggested. Reaction was proved to be a valuable method for synthesis of unsaturated organosilicon derivatives.     

Ruthenium catalyzed synthesis of enaminones

The Grubbs first-generation catalyst has been found to be an effective catalyst for the synthesis of enaminones by coupling thioamides with α-diazodicarbonyl compounds. The reaction is successful in converting primary, secondary, and tertiary thioamides into their corresponding enaminones. The reaction is also suitable for the synthesis of chiral enaminones.     

Modular synthesis of optically active lactones by Ru-catalyzed asymmetric allylic carboxylation and ring-closing metathesis reaction

A new synthetic route to optically active unsaturated γ- and δ-lactones has been demonstrated via asymmetric allylic carboxylation with a planar-chiral Cp'Ru catalyst and ring-closing metathesis reaction with a Grubbs II catalyst, and successfully applied to the enantioselective synthesis of (R)-(-)-massoialactone.     

Grubbs催化剂合成研究进展

烯烃复分解反应通过催化使两个烯烃碳碳双键断裂,再重新组合形成新的碳碳双键,是以烯烃作为底物构建碳碳双键的重要方法.从反应类型来分,烯烃复分解反应主要有：关环复分解反应（RCM）,开环复分解聚合反应（ROMP）,交叉复分解反应（CM）及非环二烯复分解反应（ADMET）.在天然产物的全合成,药物化学和材料科学中均有广     

New efficient ruthenium metathesis catalyst containing chromenyl ligand

A synthesis of new Hoveyda-Grubbs-type catalyst with chromenyl ligand was described herein. The new catalyst was tested in model RCM and CM reactions. The catalyst proved to be quite efficient. It showed activity comparable or superior to that of commercially available Grubbs second-generation complexes.     

Asymmetric synthesis of C-aliphatic homoallylic amines and biologically important cyclohexenylamine analogues

An efficient method for the asymmetric synthesis of C-aliphatic homoallylic amines with up to 94% yield and 80% de is reported. Ring-closing metathesis of several chiral homoallylic amines using the second-generation Grubbs catalyst provided easy access to a wide variety of cyclohexenylamines.     

Homo- and heterogeneous Ru-based metathesis catalysts in cross-metathesis of 15-allylestrone—towards 17β-hydroxysteroid dehydrogenase type 1 inhibitors

The cross-metathesis of allylestrone with acrylic acid derivatives using homogeneous and heterogenized Ru-catalysts was evaluated for the synthesis of a new 17β-hydroxysteroid dehydrogenase type 1 inhibitor. Hoveyda-type catalyst containing an additional diethylamino group turned out to be comparably active as homogeneous Grubbs II catalyst after immobilization on an acidic ion exchange resin which greatly facilitated workup.     

Polymer‐Bound,Amphiphilic Hoveyda‐Grubbs‐Type Catalyst for Ring‐Closing Metathesis in Water

Summary: We report on the synthesis of a new amphiphilic, polymer‐bound variant of the Hoveyda‐Grubbs catalyst via the coupling reaction of a carboxylic acid‐functionalized poly(2‐oxazoline) block copolymer with 2‐isopropoxy‐5‐hydroxystyrene and subsequent reaction of the resulting macroligand with a second generation Grubbs catalyst. For the benchmark, the substrate diethyl diallylmalonate was studied in the ring‐closing metathesis (RCM) reaction and a turn‐over number (TON) of up to 390 in water was achieved. To the best of our knowledge, this is the highest value for any aqueous RCM reaction to date. For the first time, recycling of a ruthenium initiator in an aqueous RCM reaction has been successful to some extent. In addition, the micellar conditions accelerate the conversion of the hydrophobic diene and at the same time stabilize the active alkylidene species, although competing decomposition of the catalyst in water still impairs the catalyst performance. Residual ruthenium content was determined to be below 1 ppm in the product suggesting a very low leaching of the polymeric catalyst system.

Simplified chemical structure of the amphiphilic, polymer‐bound Grubbs‐Hoveyda catalyst.     

A concise asymmetric route to the bridged bicyclic tropane alkaloid ferruginine using enyne ring-closing metathesis

[reaction: see text] Enyne metathesis has been used to prepare bridged azabicycles and applied in a short asymmetric synthesis of the tropane ferruginine. A Grubbs first generation catalyst proved to be superior to the second generation catalyst in the enyne metathesis reaction.     

Aerobic Dehydrogenation of N-Heterocycles with Grubbs Catalyst: Its Application to Assisted-Tandem Catalysis to Construct N-Containing Fused Heteroarenes

An aerobic dehydrogenation of nitrogen-containing heterocycles catalyzed by Grubbs catalyst is developed. The reaction is applicable to various nitrogen-containing heterocycles. The exceptionally high functional group compatibility of this method was confirmed by the oxidation of an unprotected dihydroindolactam V to indolactam V. Furthermore, by taking advantage of the oxygen-mediated structural change of the Grubbs catalyst, we integrated ring-closing metathesis and subsequent aerobic dehydrogenation to develop the novel assisted-tandem catalysis using molecular oxygen as a chemical trigger. The utility of the assisted-tandem catalysis was demonstrated by the concise synthesis of N-containing fused heteroarenes including a natural antibiotic, pyocyanine.     

An alternative stereoselective synthesis of greensporone C

Greensporone C, a new 14-membered resorcylic acid lactone, has been synthesized from inexpensive and commercially available starting materials. This convergent synthesis utilizes Cross metathesis using the Grubbs Hoveyda catalyst, alkylation of 1,3-dithiane and Yamaguchi macrolactonization as key steps.     

A materials approach to site-isolation of Grubbs catalysts from incompatible solvents and m-chloroperoxybenzoic acid

The development of a method for site-isolation of Grubbs second-generation catalyst from MCPBA is described. In these reactions, Grubbs catalyst was dissolved in a solvent consisting of a mixture (1:1 v/v) of 1-butyl-3-methylimidazolium hexafluorophosphate and methylene chloride and completely encapsulated within a thimble fabricated from polydimethylsiloxane (PDMS). A series of molecules that react by cross metathesis or ring-closing metathesis were added to the interior of the thimble and allowed to react. In the last step, m-chloroperoxybenzoic acid (MCPBA) dissolved in MeOH/H(2)O (1:1 v/v) was added to the exterior of the PDMS thimble. Small organic molecules diffused through the PDMS to react with MCPBA to form epoxides, but the Grubbs catalyst remained encapsulated. This result is important because Grubbs catalyst catalytically decomposes MCPBA at ratios of MCPBA to Grubbs of 3000 to 1. The yields for this two-step cascade sequence ranged from 67 to 83 %. The concept behind this sequence is that small organic molecules have high flux through PDMS but large molecules--such as Grubbs catalyst--and ionic reagents--such as MCPBA--have much lower flux through PDMS. Small molecules can thus react both outside and inside PDMS thimbles, whereas incompatible catalysts and reagents remain site-isolated from each other. This method does not require alteration of structures of the catalysts or reagents, so it may be applied to a wide range of homogeneous catalysts and reagents. To demonstrate further that the catalyst was encapsulated, the Grubbs catalyst was successfully recycled within the cascade sequence.     

Highly chemo- and stereoselective intermolecular coupling of diazoacetates to give cis-olefins by using Grubbs second-generation catalyst

Highly stereoselective formation of cis-2-ene-1,4-diesters by homo- and heterocoupling of alpha-diazoacetates in the presence of Grubbs second-generation catalyst is demonstrated. The dual reactivity of the catalyst in alkene metathesis and diazocoupling has been exploited in the synthesis of 12-26-membered macrocyclic dienyl dilactones by one-pot carbene dimerisation/ring-closing metathesis.     

Kinetically controlled ring-closing metathesis: synthesis of a potential scaffold for 12-membered salicylic macrolides

For the synthesis of a 12-membered salicylic macrolide scaffold, ring-closing metathesis (RCM) of a omega-diene compound was planned. The stereochemical outcome of the RCM reaction changed depending on the type of Ru catalyst that was used; a "first-generation" Grubbs catalyst produced exclusively the E isomer and "second-generation" catalysts provided a mixture of the E and Z isomers under kinetic control (not thermodynamic control). Considerations for the E/Z selectivity are described.     

Enantioselective total synthesis of (-)- and (+)-petrosin

The enantioselective total synthesis of (-)- and (+)-petrosin is described. The union of two key segments was executed by Suzuki-Miyaura coupling. The quinolizidine rings were stereoselectively constructed via a diastereoselective Mannich reaction and an aza-Michael reaction. The 16-membered ring was constructed by ring-closing metathesis with the second-generation Grubbs catalyst.     

Facile synthesis of substituted 2,3,4,7-tetrahydro-1H-azepines via ring-closing metathesis

A highly efficient synthesis based on inexpensive and readily available starting material towards the pharmacologically interesting class of substituted 2,3,4,7-tetrahydro-1H-azepines via a ring-closing metathesis (RCM) approach employing Grubbs catalysts 1 and 2 is described. The influence of the substituents R¹ and R² on the outcome of the RCM reaction is discussed. The seemingly first example of an RCM approach towards seven-membered azacycles bearing a substituent at the alkene moiety utilizing Grubbs catalyst 1 is presented.     

Synthesis and activity for ROMP of bidentate Schiff base substituted second generation Grubbs catalysts

The synthesis and characterisation of Schiff base substituted second generation Grubbs catalysts is described using the pyridine functionalised second generation catalyst and a Schiff base-Tl salt. The complexes are less active for the ROMP of COD (cycloocadiene) than their second generation analogues though their activity for the ROMP of DCPD (dicyclopentadiene) at high temperatures shows great potential due to the thermal stability of the catalysts.     

Strategic utilization of catalytic metathesis and photo-thermal metathesis in caged polycyclic frames

Highly functionalized cage compounds have been prepared via cross-metathesis (CM) using Grubbs modified N-tolyl catalyst 7. A strategic utilization of photo-thermal metathesis and catalytic metathesis sequence for the synthesis of functionalized caged molecules has been demonstrated.     

Development of isomerization and cycloisomerization with use of a ruthenium hydride with N-heterocyclic carbene and its application to the synthesis of heterocycles

A pure ruthenium hydride complex with N-heterocyclic carbene (NHC) ligand was efficiently generated from the reaction of a second-generation Grubbs ruthenium catalyst with vinyloxytrimethylsilane and unambiguously characterized. This ruthenium hydride complex showed high catalytic activity for the selective isomerization of terminal olefin and for the cycloisomerization of 1,6-dienes. These reactions of N-allyl-o-vinylaniline lead to novel synthetic methods for heterocycles such as indoles and 3-methylene-2,3-dihydroindoles, which are useful synthons for bioactive natural products. These procedures address an important issue in diversity-oriented synthesis.     

Improved synthesis of the A-G ring segment of brevetoxin B

An efficient synthesis of the A-G ring segment 2, a key intermediate for the total synthesis of brevetoxin B (1), was achieved in 37 steps and 5.0% overall yield. The intramolecular allylation of the O,S-acetal 22, prepared from the ABC ring segment 15 and the FG ring segment 17, was carried out using AgOTf as a Lewis acid to give the desired compound 23, predominantly. Ring-closing metathesis of 23 with the Grubbs catalyst 12 afforded the heptacyclic ether 25. Selective hydrogenation of the E ring olefin of 25 was performed by diimide reduction to afford 2.