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Samarium metal and samarium diiodide have become important tools as selective cyclopropanating agents in organic synthesis due to their high chemo- and stereoselectivity. Therefore, Sm and SmI2are the ideal reagents to prepare cyclopropane derivatives. This tutorial reviewhighlights C–C multiple bond cyclopropanation processes promoted by samarium or samarium diiodide. [ABSTRACT FROM AUTHOR]

The free-radical hydrothiolation of alkynes (thiol-ynecoupling, TYC) unites two thiol fragments across the carbon-carbon triple bond to give a dithioether derivative with exclusive 1,2-addition; this reaction can be used for modification of peptides and proteins allowing glycoconjugation and fluorescent labeling. These results have implications not only as a flexible strategy for attaching two modifications at a single site in proteins but also for unanticipated side-reactions of reagents (such as cycloalkynes) used in other protein coupling reactions. [ABSTRACT FROM AUTHOR]

The intramolecular [2 + 2]-photocycloaddition of the 1,3-divinyl-2-cyclopentyl tetronates 1 was performed under various conditions to give perfect diastereoselectivity and a regioselectivity of up to 85/15 in the presence of γ-cyclodextrin by differentiating the two chemically very similar double bonds of 1. [ABSTRACT FROM AUTHOR]

Reactions and purifications, including carbon–carbon bond forming reactions, can be carried out on a cellulose support on which the substrates are non-covalently absorbed. [ABSTRACT FROM AUTHOR]

Transition-metal-catalyzed coupling reactions have become a versatile tool for chemical bond formation. From the variation of the coupling partners, coupling reactions can be classified into three models: traditional coupling, reductive coupling and oxidative coupling. The oxidative coupling, which is different from the traditional coupling, occurs between two nucleophiles. This critical reviewfocuses on transition-metal-catalyzed oxidative coupling reactions involving organometallic reagents as nucleophiles. Since the scope of the oxidative coupling is highly diversified, this paper only reviews the oxidative coupling reactions concerning C–C bond formation, including the coupling between organometal reagents and hydrocarbons as well as coupling between two organometal reagents. Since terminal alkynes are normally activated by metal salts and in situform the alkynyl metal reagents in coupling reactions, they are directly considered as organometal reagents in this review. Intramolecular oxidative couplings and oxidative cyclizations are not included in this critical review. Moreover, there are many examples of oxidative coupling leading to the formation of functional materials, such as the oxidative polymerization of thiophenes. Since several reviews in these areas have been published they are not included in this review either (99 references). [ABSTRACT FROM AUTHOR]

Fagnou et al.reported direct arylation reactions that use palladium catalysts to couple Ar1–X to Ar2–H with the aid of a coordinated base. These reactions are particularly favourable for polyfluorinated arenes Ar2–H (see S. I. Gorelsky, D. Lapointe and K. Fagnou, J. Am. Chem. Soc. 2008, 130, 10848). In this paper, we show by means of a DFT analysis how the energetics and activation energies vary with fluorine substitution and examine the structures of intermediates and transition states. The reactant is modelled by Pd(OAc)(Ph)(PMe3)(DMA) (DMA = dimethylacetamide). The sequence consists of (a) replacement of DMA by arene, (b) Concerted Deprotonation Metallation (CMD), (c) decoordination of AcOH, (d) reductive elimination of biaryl. Many of the variations are dominated by the number of fluorine substituents orthoto the C–H bond and fall into three groups labelled accordingly: Set0Fo, Set1Fo, and Set2Fo. In the first step a coordinated solvent is replaced by the arene. The arenes of Set0Foand Set1Focoordinate in a conventional η2-CHCH mode, whereas the arenes of Set2Focoordinate in an η1-CH mode assisted by an OH–C hydrogen bond from the coordinated acetate. Both the energy barriers to CMD and the product energies fall into the three typical sets with the highest barrier and highest product energy being for Set0Fo. They correlate more satisfactorily with the variations in Pd–C bond energies than with the C–H acidities. The barriers to reductive elimination from Pd(Ph)(ArF)(PMe3)(AcOH) increase systematically from Set0Foto Set2Foas the Pd–C bond becomes stronger in a regular fashion from Set0Foto Set2Fo. Again there is a strong correlation between the energy barriers to reductive elimination and the Pd–C bond energies. It is found overall that the key aspects of the reactions are: (a) the lowering of the energy of the CMD step by the orthofluorine substituents, (b) the regioselective activation of C–H bonds orthoto fluorine which is also determined at the CMD step, (c) the decoordination of AcOH, which maintains the transition state for reductive elimination at low Gibbs free energy. The presence of fluorine increases the effectiveness of the reaction in the sense of points a and b viathe increasing strength of the palladium-carbon bond. [ABSTRACT FROM AUTHOR]

In this paper, we present a theoretical study based on DFT methods using functionals implemented in Gaussian03, to obtain geometry optimizations, harmonic frequencies, IR intensities and Raman scattering activities of the triad [Ni(tdas)2]z[z= 0 (0); z= 1− (1); z= 2− (2)] and of [Au(tdas)2]−(3) with the aim of elucidating the nature of the bonding in these complexes and checking whether C–C stretching vibrations are suitable spectroscopic markers to assign the ‘innocent–non-innocent’ character of the ligand. Geometry optimization at the density functional theory level was performed, and geometrical parameters were obtained in good agreement with the experimental structural data for the Ni complexes. Following the geometrical changes upon reduction, the Ni–S, N–S and C–S distances undergo a small increase, while the C–C length does not change significantly. Thus, unlike what is generally found for non-benzenoid dithiolenes, no shift of the ν(C–C) vibration is expected on reduction as observed for 1and 2. The vibrational spectra are very accurately reproduced by the calculations. The less satisfactory agreement obtained for the gold complex is probably due to the deviation of the structurally characterized sample from the D2hsymmetry obtained in the calculations, and/or overestimation of the Au–S distances, typical of the DFT functionals used. Calculations indicated that the electroactive orbital, HOMO in 2and 3, SOMO in 1and LUMO in 0, is a highly delocalized π-orbital with a predominant S-ligand character, and that the total spin density in 1is delocalized over the ligands and the nickel atom, in agreement with EPR data. From the obtained results we can assign a non-innocent character to the tdas ligand and show that the C–C stretching vibrations are not suitable spectroscopic markers to reflect this feature. [ABSTRACT FROM AUTHOR]