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Enantioselective copper-catalyzed allylic alkylations were performed on allylic bromides with a protected hydroxyl or amine functional group using several Grignard reagents and Taniaphos L1 as a ligand. The terminal olefin moiety in the products was transformed into various functional groups without racemization, providing facile access to a variety of versatile bifunctional chiral building blocks. [ABSTRACT FROM AUTHOR]

A computational DFT examination (B3LYP/6-31G* and B3LYP/6-311+G**//B3LYP/6-31G*) of the thermal [5C + 2C] cycloaddditions of 6-acetoxy-3-pyranones and 3-silyloxy-4-pyrones with tethered alkenyl sulfoxides confirms that the high level of diastereofacial selectivity obtained is ultimately due to the preference of the alkenesulfinyl group to adopt a well-defined conformation in the transition state of the reaction. This conformation, which is different from that found in the ground state, is most probably dictated by dipolar interaction effects between the sulfoxide and the oxidopyrylium ylide intermediate. [ABSTRACT FROM AUTHOR]

Examines the production of branched allylic ethers using iridium catalysts. Intermolecular allylic etherification of achiral carbonates with phenoxides; Molecular structure; Enantioselectivity.

Examines the ruthenium-catalyzed alkyne-alkene coupling and a prins-type cyclization. Use of 1-trimethylsilyl-1-alkyn-3-ols and allyl ethers; Application of aromatic system as the nucleophilic partner; Assembly of a homologous oxygen-bridged system.

A highly diastereo- and chemoselectiveintramolecular nickel-catalyzedcycloaddition of alkene- and alkyne-tethered alkynylidenecyclopropanesis reported. The method constitutes the first fully intramolecular[3 + 2 + 2] alkylidenecyclopropropane cycloaddition occurring viaa proximal cleavage of the cyclopropane and makes it possible to buildrelevant 6,7,5-tricyclic frameworks in a single-pot reaction. Importantly,the reaction outcome is highly dependent on the characteristics ofthe nickel ligands. [ABSTRACT FROM AUTHOR]

Thecomplex [OsCp{κ3-P,C,C-PiPr2[C(CH3)CH2]}(CH3CN)]PF6(1) reactswith (2-pyridyl)methylenecyclopropane, at room temperature, to giveinitially the cyclobutylidene derivative [Os(η5-C5H5)(CCH2CH2CH-o-C5H4N){PiPr2[C(Me)CH2]}]PF6(2), as a result of the ring expansionof the alkylidenecyclopropane unit. Over time complex 2rearranges into the cyclobutene derivative [Os(η5-C5H5){η2-C(CHCH2CH2)-o-C5H4N}{PiPr2[C(Me)CH2]}]PF6(3). The reaction of 1with (2-pyridyl)methylenecyclopropane at room temperaturealso affords the phosphinomethanide metallacycle [Os(η5-C5H5){κ4-P,Ca,Cb,N-PiPr2[Ca(Me)CH2CH)(CbCH2CH2-o-C5H4N]}]PF6(4) as a minor product, which becomes the major product of the reactionat 45 °C. This osmacyclopentane results from the C–C couplingof the isopropenyl substituent of the phosphine ligand and the organicsubstrate. In acetone at 75 °C, the reaction of 1with (2-pyridyl)methylenecyclopropane leads to the 2-alkylidene-1-osmacyclobutane[Os(η5-C5H5){κ3-N,Ca,Cb-Ca(CH2CbH2)(CH-o-C5H4N)}{PiPr2[C(Me)CH2]}]PF6(5), as a consequence of the oxidative addition ofone of the C(sp2)–C(sp3) bonds of thecyclopropane unit of the substrate to the osmium atom, along with 6, a diastereomer of 4. Complexes 3–5have been characterized by X-ray diffractionanalysis. DFT calculations suggest that all of the reaction productsare derived from a common key 1-osma-2-azacyclopent-3-ene intermediate(D). [ABSTRACT FROM AUTHOR]

A practical protocol for the hydroalkynylation of enones using Pd catalysis is reported. The reaction proceeds efficiently with a variety of alkynes as well as with several cyclic and acyclic enones, providing synthetically relevant β-alkynyl ketones in good to excellent yields. [ABSTRACT FROM AUTHOR]

Gold(I) complexes featuring electron acceptor ligands such as phosphites and phosphoramidites catalyze the [4C+2C] intramolecular cycloaddition of allenedienes. The reaction is chemo- and stereoselective, and provides trans-fused bicyclic cycloadducts in good yields. Moreover, using novel chiral phosphoramidite-based gold catalysts it is possible to perform the reaction with excellent enantioselectivity. Experimental and theoretical data dismiss a cationic mechanism involving intermediate II and suggest that the formation of the [4C+2C] cycloadducts might arise from a 1,2-alkyl migration (ring contraction) in a cycloheptenyl Au-carbene intermediate (IV), itself arising from a [4C+3C] concerted cycloaddition of the allenediene. Therefore, these [4C+2C] allenediene cycloadditions and the previously reported [4C+3C] counterparts most likely share such cycloaddition step, differing in the final 1,2-migration step. [ABSTRACT FROM AUTHOR]

The article describes the [4+3] intramolecular cycloaddition of alkylidenecyclopropanes and dienes using a palladium catalyst. According to the authors, the cycloaddition reaction allows the synthesis of appealing, stereochemically rich 5,7-fused bicyclic systems from readily dienylidenecyclopropanes. They mention that the success of reaction is restricted to dienes blocked in a cisoid conformation and activated by the presence of electron-withdrawing substituents.

This article presents information related to an iterative catalytic route to enantiopure deoxypropionate subunits. The occurrence of polydeoxypropionate chains in numerous biologically relevant compounds has stimulated the development of methods for their stereocontrolled synthesis. The poor results obtained in the 1,4 additions of the less reactive MeMgBr impeded the development of catalytic iterative methodology for 1,3-dimethyl arrays. The additions of MeMgBr proceed with equally high selectivity when the catalyst loading is reduced to only 1 mol %, providing the methylated 1,4-addition products with 92- 96% ee and isolated yields of 88-94%.

α,β-Unsaturated N,N-dialkyl hydrazones undergo a mild [2+ 2] cycloaddition to allenamideswhen treated with a suitable gold catalyst. The method, which representsthe first application of N,N-dialkylhydrazones in gold catalysis, is compatible with a wide variety ofsubstituents at the alkenyl moiety of the hydrazone component, proceedswith excellent levels of regio- and diastereoselectivity, and providesdensely substituted cyclobutanes with good to excellent yields. [ABSTRACT FROM AUTHOR]

The first highly enantioselective intermolecular (4 + 2) cycloaddition between allenes and dienes is reported. The reaction provides good yields of optically active cyclohexenes featuring diverse substitution patterns and up to three stereocenters. Key to the success of the process is the use of newly designed axially chiral N-heterocyclic carbene-gold catalysts. [ABSTRACT FROM AUTHOR]

We report a ruthenium-catalyzed (2 + 2) intramolecular cycloadclition of allenes and alkenes. We have found that the use of the ruthenium complex nH2Cl2(PiPr3)2., which has previously gone unnoticed in catalytic applications, is crucial for the observed reactivity. The reaction proceeds under mild conditions and is fully diastereoselective, providing a practical entry to a variety of bicydo[3.2.O]heptane skeletons featuring cyclobutane rings. [ABSTRACT FROM AUTHOR]

The article focuses on the potential applications of the cleavage of C-C bonds with the help of transition-metal complexes in organic synthesis, as well as petroleum and pharmaceutical research. It says that alkylidenecyclopropanes containing C=C bond at the olefinic moiety's terminal carbon undergo Os-promoted ring expansion. It cites that absence of coordination auxiliary can be cracked to ethylene and vinylidene units under very mild conditions to form ethylene-osmium-vinylidene complexes.

The article focuses on the formation of cyclobutylidine complexes from osmium and ruthenium through the ring expansion of alkylidenecyclopropanes. It mentions that new reaction transition pattern of metal complexes and alkylidenecyclopropane formed the derivatives of cyclobutylidene. It concludes that alkalidenecyclopropanes that contains chelation assistant undergo ring expansion to afford cyclobutylidene derivatives.