Copper‐catalyzed Ullmann condensations are key reactions for the formation of carbon–heteroatom and carbon–carbon bonds in organic synthesis. These reactions can lead to structural moieties that are prevalent in building blocks of active molecules in the life sciences and in many material precursors. An increasing number of publications have appeared concerning Ullmann‐type intermolecular reactions for the coupling of aryl and vinyl halides with N, O, and C nucleophiles, and this Minireview highlights recent and major developments in this topic since 2004. 相似文献
The transformation of C? H bonds into other chemical bonds is of great significance in synthetic chemistry. C? H bond‐activation processes provide a straightforward and atom‐economic strategy for the construction of complex structures; as such, they have attracted widespread interest over the past decade. As a prevalent directing group in the field of C? H activation, the amide group not only offers excellent regiodirecting ability, but is also a potential C? N bond precursor. As a consequence, a variety of nitrogen‐containing heterocycles have been obtained by using these reactions. This Focus Review addresses the recent research into the amide‐directed tandem C? C/C? N bond‐formation process through C? H activation. The large body of research in this field over the past three years has established it as one of the most‐important topics in organic chemistry. 相似文献
Electroactive fused ethylenedithio? tetrathiafulvalene? [4]helicene and ‐[6]helicenes have been synthesized through a strategy that involved the preparation of 2,3‐dibromo‐helicene derivatives as intermediates. The dihedral angles between the terminal helicenes, as determined by single‐crystal X‐ray analysis, are 22.7° and 50.7° for the [4]helicene and [6]helicene, respectively. Their solid‐state architectures show interplay between S???S and π???π intermolecular interactions. The chiroptical properties of the enantiopure EDT? TTF? [6]helicene derivatives have been investigated and supported by TDDFT calculations. Remarkable redox switching of the circular dichroism (CD) signal between the neutral and radical‐cation species has been achieved. 相似文献
A nanocomposite of Pd? TiO2? SiO2 is developed through a sol‐gel process from the reaction products of titanium isopropoxide followed by mixing the same with palladium linked 3‐glycidoxypropyltrimethoxysilane. The reaction product is sonicated and calcinated to obtain the nanocomposite of Pd? TiO2? SiO2. The calcination at 600 °C yielded an amorphous structure whereas at 900 °C it resulted into a nanocrystalline structure. The nanocomposite of palladium was further characterized by TEM, XRD, IR and EDS. The material acts as an efficient electrocatalyst. Electrocatalysis of ascorbic acid is observed at 0.1 V vs. Ag/AgCl, shows linearity between 1 µM and 1 mM in 0.1 M phosphate buffer (pH 7.0). 相似文献
Tuning the nature of the linker in a L∼BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ‐C H and ε‐Bsp2 H, agostic interactions. Such a unique coordination mode stabilizes a 14‐electron “RuH2P2” fragment through connected σ‐bonds of different polarity, and affords selective B H, C H, and B C bond activation as illustrated by reactivity studies with H2 and boranes. 相似文献
An sp 2 /sp 3 get‐together : A novel and efficient method can be used to synthesize 3,3‐disubstitued oxindoles by the direct intramolecular oxidative coupling of an aryl C? H and a C? H center (see scheme; DMF=N,N‐dimethylformamide).
Attachment of one electron to 1,2-diBeX-benzene and 1,2-diZnX-benzene derivatives leads to the formation of stronger Be Be and Zn Zn interaction compared to the neutral one. This is reflected in the dramatic shortening of the Be Be and Zn Zn distance. The formation of these 2-center-1-electron bonds have also been confirmed by topological survey of electron density using quantum theory of atoms in molecules and electron localization function. The formation of these bonds is expected to render stability to these radical anions. These radical anions are stable toward electron detachment and computed bond dissociation energy values are also significant. 相似文献
Described herein is a manganese‐catalyzed dehydrogenative [4+2] annulation of N H imines and alkynes, a reaction providing highly atom‐economical access to diverse isoquinolines. This transformation represents the first example of manganese‐catalyzed C H activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H2 as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition‐metal‐catalyzed C H activation. Mechanistic studies revealed the five‐membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle. 相似文献
The reactivity of disulfide and diselenide derivatives towards F? and CN? nucleophiles has been investigated by means of B3PW91/6‐311+G(2df,p) calculations. This theoretical survey shows that these processes, in contrast with the generally accepted view of disulfide and diselenide linkages, do not always lead to S? S or Se? Se bond cleavage. In fact, S? S or Se? Se bond fission is the most favorable process only when the substituents attached to the S or the Se atoms are not very electronegative. Highly electronegative substituents (X) strongly favor S? X bond fission. This significant difference in the observed reactivity patterns is directly related to the change in the nature of the LUMO orbital of the disulfide or diselenide derivative as the electronegativity of the substituents increases. For weakly electronegative substituents, the LUMO is a σ‐type S? S (or Se? Se) antibonding orbital, but as the electronegativity of the substituents increases the π‐type S? X antibonding orbital stabilizes and becomes the LUMO. The observed reactivity also changes with the nature of the nucleophile and with the S or Se atom that undergoes the nucleophilic attack in asymmetric disulfides and diselenides. The activation strain model provides interesting insights into these processes. There are significant similarities between the reactivity of disulfides and diselenides, although some dissimilarities are also observed, usually related to the different interaction energies between the fragments produced in the fragmentation process. 相似文献
The Morita? Baylis? Hillman (MBH) reactions of (4S,5R,7R,8R)‐ and (4R,5R,7R,8R)‐4‐hydroxy‐7,8‐dimethoxy‐7,8‐dimethyl‐6,9‐dioxaspiro[4.5]dec‐2‐en‐1‐ones ( 2 and 3 , resp.) with aldehydes using various catalysts were studied. A combination of Bu3P/phenol in THF was found being optimum conditions giving the corresponding MBH adducts with high diastereoisomeric ratios. After separation, each stereomerically pure isomer of the MBH adducts was subjected to hydrolysis employing 1% aq. CF3COOH (TFA) in a water bath of an ultrasonic cleaner to afford the corresponding polyhydroxylated cyclopentenones in good yields. 相似文献
A computational study of the intramolecular pnicogen bond in PHF? (CH2)n? PHF (n=2–6) systems was carried out. For each compound, two different conformations, (R,R) and (R,S), were considered on the basis of the chirality of the phosphine groups. The characteristics of the closed conformers, in which the pnicogen interaction occurs, were compared with those of the extended conformer. In several cases, the closed conformations are more stable than the extended conformations. The calculated interaction energies of the pnicogen contact, by means of isodesmic reactions, provide values between ?3.4 and ?26.0 kJ mol?1. Atoms in molecules and electron localization function analysis of the electron density showed that the systems in the closed conformations with short P ??? P distances have a partial covalent character in this interaction. The calculated absolute chemical shieldings of the P atoms showed an exponential relationship with the P ??? P distance. In addition, a search in the Cambridge crystallographic database was carried out to detect those compounds with a potential intramolecular pnicogen bond in the solid phase. 相似文献
New conjugates of antiviral nucleoside Ribavirin (=1‐(β‐D ‐ribofuranosyl)‐1H‐1,2,4‐triazole‐3‐carboxamide; 1 ) with 1,2‐ and 1,3‐diacyl glycerophosphates have been synthesized by the phosphoramidite method. A combination of 2′,3′‐phenylboronate protecting group for the sugar moiety of the ribonucleoside 1 and 2‐cyanoethyl protection for the phosphate fragment ensured the preparation of the desired compounds with reasonable yields via a small number of synthetic steps. 相似文献