Construction of a novel Mo/Cu/S cluster with a closed double-cubane-like polyhedron and a chain polymer of W/Cu/S clusters

Reaction of [MoOS(3)](2)(-) and [WS(4)](2)(-) with Cudtp (dtp = diethyl dithiophosphate) gave rise to the clusters [Bu(4)N](2)[(MoOS(3))(4)Cu(12)(dtp)(6)], 1, and [Et(4)N][(WS(4)Cu(4))(dtp)(3)], 2, respectively. In cluster 1, the dtp- ligands act as both monodentate and bidentate ligands that bridge between Cu atoms and link together a closed double-cubane-like [Mo(2)O(2)S(6)Cu(6)](2+) core and two incomplete cubane-like [MoOS(3)Cu(3)]+ units. In cluster 2, the [WS(4)Cu(4)](2+) fragments were connected via bidentate and doubly bridging dtp- bridges to give a chain polymeric anion. Cluster 1 is the first example of a Mo/Cu/S cluster that contains a closed double-cubane-like structure. Compound 2 is also rare and the first W/Cu/S polymer with dtp- linkages.     

Systematic synthesis of heterometallic Ni/Fe/S and Cu/Fe/S clusters with a pentlandite-like M8S6 core

The systematic synthesis of heterometallic Ni/Fe/S and Cu/Fe/S clusters with a M8S6 core structure that resembles that of pentlandite minerals is described. The chemical properties and electronic structures of the new clusters have been investigated and are reported in this communication.     

A quadruple ring-closing metathesis reaction in the synthesis of bis-spirocyclic compounds: extending the scope of metathesis chemistry

The first example of a quadruple ring-closing metathesis reaction is reported. The reaction of the C2 symmetric octaene 3 afforded bis-spirocyclic compounds in high yield.     

Reversible aqueous metathesis reactions for potential application in dynamic combinatorial chemistry

Solutions of heterocycles having an allyl sulfide unit and simple alkenes in 50% t-BuOH/H₂O undergo reversible olefin metathesis reactions with the second generation Hoveyda-Grubbs catalyst. The choice of functional groups is limited by competitive chelation of some heterocycles with the catalyst, and other stereoelectronic effects.     

Modeling random methyl branching in ethylene/ propylene copolymers using metathesis chemistry: synthesis and thermal behavior

The structure of random ethylene/propylene (EP) copolymers has been modeled using step polymerization chemistry. Six ethylene/propylene model copolymers have been prepared via acyclic diene metathesis (ADMET) polymerization and characterized for primary and higher level structure using in-depth NMR, IR, DSC, WAXD, and GPC analysis. These copolymers possess 1.5, 7.1, 13.6, 25.0, 43.3, and 55.6 methyl branches per 1000 carbons. Examination of these macromolecules by IR and WAXD analysis has demonstrated the first hexagonal phase in EP copolymers containing high ethylene content (90%) without the influence of sample manipulation (temperature, pressure, or radiation). Thermal behavior studies have shown that the melting point and heat of fusion decrease as the branch content increases. Further, comparisons have been made between these random ADMET EP copolymers, random EP copolymers made by typical chain addition techniques, and precisely branched ADMET EP copolymers.     

Low-temperature synthesis of uranium tetraboride by solid-state metathesis reactions

A novel synthesis of uranium tetraboride (UB(4)) by solid-state metathesis reaction is demonstrated. This approach significantly lowers the temperature required to synthesize this material to < or = 850 degrees C. When UCl(4) is reacted with 2 equiv of MgB(2) at 850 degrees C, crystalline UB(4) is formed. Powder X-ray diffraction and ICP-AES data support the reduction of UCl(4) to UCl(3) as the initial step in the reaction. The UB(4) product is purified by washing with water.     

Ring-closing olefin metathesis reactions; synthesis of iso-β-bisabolol

A ring-closing olefin metathesis is the key step in a synthesis of the rare iso-β-bisabolol found in sandalwood oils.     

Asymmetric synthesis of fluorinated amino macrolactones through ring-closing metathesis

The synthesis of new chiral fluorinated amino and azamacrolactones of types 1 and 2 is described. A ring-closing metathesis (RCM) reaction constitutes the key step in this methodology, which uses fluorinated amino alcohols 7 as starting materials. The influence of the CF2 group, which is located in the alpha-position relative to the carbon bearing the amino group, on the efficiency of the RCM reaction is noteworthy. This method allows for the preparation of the desired fluorinated macrolactones in excellent yields.     

Catalytic asymmetric ring-opening metathesis/cross metathesis (AROM/CM) reactions. Mechanism and application to enantioselective synthesis of functionalized cyclopentanes

Studies regarding the first examples of catalytic asymmetric ring-opening metathesis (AROM) reactions are detailed. This enantioselective cleavage of norbornyl alkenes is followed by an intermolecular cross metathesis with a terminal olefin partner; judicious selection of olefin is required so that oligomerization and dimerization side products are avoided. Results outlined herein suggest that the presence of suitably positioned heteroatom substituents may be critical to reaction efficiency. Mo-catalyzed tandem AROM/CM affords functionalized cyclopentyl dienes in >98% ee and >98% trans olefin selectivity; both secondary and tertiary ether products can be obtained. The examples provided include the catalytic synthesis of an optically pure cyclopentyl epoxide and dimethyl acetal. Mechanistic studies suggest that it is the more substituted benzylidene or silylated alkylidenes that are involved in the catalytic process (vs the corresponding Mo-methylidenes). Although electron rich benzylidenes react more efficiently, the derived electron poor Mo complexes promote AROM/CM transformations as well; alkylidenes that bear a boron substituent are unreactive.     

Total synthesis of patulolide A through ring closing metathesis

A simple and efficient total synthesis of patulolide A from readily available 7-octen-1-ol is reported by asymmetric synthetic approach. The key reactions involved are asymmetric dihydroxylation using AD-mix-β and Grubbs’ ring-closing metathesis reaction for the synthesis macrocyclic ring system.     

Regioselective synthesis of novel spiroindane-1,3-diones through 1,3-dipolar cycloaddition reactions

A facile synthesis of novel spiroindane-1,3-diones has been achieved via 1,3-dipolar cycloaddition of an azomethine ylide, generated in situ from ninhydrin and 1,2,3,4-tetrahydroisoquinoline, with the conjugated double bond of chalcone derivatives. The regiochemistry and structures of the cycloadducts were determined with spectroscopic data and by X-ray crystal structure analysis.     

Tandem radical reactions and ring-closing metathesis. Application in the synthesis of cyclooctenes

[reaction: see text] Fumarate- and acrylate-substituted oxazolidinones undergo tandem radical reaction to form dienes in moderate to good yields. The resulting dienes provide cyclooctenes in moderate to good yields after ring-closing metathesis (RCM). The role of the carbon backbone substituents and other variables in the efficiency of the eight-membered ring formation is discussed.     

Structural diversity through ligand flexibility: two novel metal-organic nets via ligand-to-ligand cross-linking of "paddlewheels"

Solvothermal reaction of a partially flexible ligand, H(4)L, and Cu(NO(3))(2)·2.5H(2)O afforded two cross-linked Kagomé lattices of formula [Cu(2)(L)](n): an acs net sustained by novel trigonal prismatic supermolecular building blocks (SBBs) and the first example of a partially pillared Kagomé net.     

Stereochemical diversity through cyclodimerization: synthesis of polyketide-like macrodiolides

[reaction: see text] An expeditious procedure for the direct formation of stereochemically well-defined macrodiolides is described. Cyclodimerizations of enantioenriched C7 and C8 hydroxy esters 6 in the presence of catalytic amounts of distannoxane transesterification catalysts afford 14- to 22-membered macrodiolides 7-9 bearing up to six stereocenters. Additional structural diversity is introduced by further stereoselective reactions on selected macrodiolides 7a, 7g, 10a, and 11.