Metal‐Catalyzed C−H Bond Activation of 5‐Membered Carbocyclic Rings: A Powerful Access to Azulene,Acenaphthylene and Fulvene Derivatives

Azulene, acenaphthylene and fulvene derivatives exhibit important physical properties useful in materials chemistry as well as valuable biological properties. Since about two decades ago, the metal‐catalyzed functionalization of such compounds, via C?H bond activation of their 5‐membered carbocyclic ring, proved to be a very convenient method for the synthesis of a wide variety of azulene, acenaphthylene and fulvene derivatives. For such reactions, there is no need to prefunctionalize the 5‐membered carbocyclic rings. In this review, the progress in the synthesis of azulene, acenaphthylene and fulvene derivatives via metal‐catalyzed C?H bond activation of their 5‐membered carbocyclic ring are summarized.     

Limites dégénérées de séries discrètes, formes automorphes et variétés de Griffiths–Schmid: le cas du groupe U (2, 1)

Let G be an inner anisotropic form of an unitary group of 3 variables over Q, such that G_RU(2,1), and be an automorphic representation of G(A) whose archimedean component is a degenerate limit of discrete series; such a never occurs in the cohomology (coherent or étale) of a Shimura variety. We show that however it does appear in the coherent cohomology of some line bundle over an associated Griffiths-Schmid variety. Moreover we study cup products between such cohomology classes and some other automorphic cohomology classes and we prove some non-vanishing results.     

Hidden constructions in abstract algebra (6): The theorem of Maroscia and Brewer & Costa

We give a constructive deciphering for a generalization of the Quillen-Suslin theorem due to Maroscia and Brewer & Costa stating that finitely generated projective modules over , where is a Prüfer domain with Krull dimension ≤1, are extended from .     

Position-independent chemical quantitation with passive 13.56-MHz radio frequency identification (RFID) sensors

Recently, we have demonstrated an attractive approach to adapt conventional radio frequency identification (RFID) tags for multianalyte chemical sensing. These RFID sensors could be very attractive as ubiquitous distributed remote sensor networks. However, critical to the wide acceptance of the demonstrated RFID sensors is the analyte-quantitation ability of these sensors in presence of possible repositioning errors between the RFID sensor and its pickup coil. In this study, we evaluate the capability for such position-independent analyte quantification using multivariate analysis tools. By measuring simultaneously several parameters of the complex impedance from such an RFID sensor and applying multivariate statistical analysis methods, we were able to compensate for the repositioning effects such as baseline signal offset and magnitude of sensor response to an analyte.     

Palladium/tetraphosphine catalyzed suzuki cross‐coupling of heteroarylboronic acids with aryl halides

cis,cis,cis‐1,2,3,4‐Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C₃H₅)]₂ efficiently catalyses the Suzuki reaction of heteroarylboronic acids with aryl bromides and also the coupling of arylboronic acids with heteroaryl bromides. The coupling of thiophene‐ or benzothiopheneboronic acids, furan‐ or benzofuranboronic acids and 3‐pyridineboronic acid with a variety of aryl bromides gave the corresponding coupling products in good yields. However, in most cases, better results in terms of ratio substrate/catalyst were obtained for the reverse reaction using heteroaryl bromides with arylboronic acids.     

A combined spectroscopic and theoretical study of dibutyltin diacetate and dilaurate in supercritical CO2

Two organotin catalysts, namely, dibutyltin dilaurate (DBTDL) and dibutyltin diacetate (DBTDA), commonly used in the synthesis of polyurethanes, have been investigated combining vibrational spectroscopic measurements with molecular modeling. The structure and vibrational spectra of the DBTDA molecule have been simulated using density functional theory. Thus, because of the Sn...O interactions, the lowest energy conformer reveals an asymmetrically chelated structure of the acetate groups with a C2v symmetry. The experimental IR spectra of DBTDA and DBTDL diluted in carbon tetrachloride and in supercritical CO2 show unambiguously that these molecules adopt the asymmetrically chelated conformation in the solvent. A new attribution of the main peaks constituting the respective IR spectra of the catalysts could be carried out. Finally, from the IR spectra of the two catalysts diluted in supercritical CO2 reported as a function of time, it was found that both molecules react slightly with CO2. However, their spectrum remains unchanged at the earliest stage of the polymerization, indicating that these molecules preserve a catalytic activity similar to that noted in conventional organic solvent.     

Substituent effects on the ring-chain tautomerism of some 1,3-oxazolidine derivatives

The 14 and 70 eV electron ionization mass spectra of five sets (R1 = Me, Et, i-Pr, t-Bu and Ph) of seven 2-aryl-4-R1-substituted (Ar = C6H4X; X = p-NO2, m-Br, p-Cl, H, p-Me, p-OMe and p-NMe2) (1-5) and of seven 2-aryl-5-phenyl-substituted 1,3-oxazolidines (6; for Ar, see above) were recorded to study their ring-chain equilibria in the gas phase. These equilibria were also studied by 1H NMR spectroscopy in CDCl3 for compounds 5 and 6. A few 2,4- and 2,5-dimethyl-2-aryl derivatives (7, 8: Ar = C6H4X; X = m-Br, H and p-OMe) were studied both in CDCl3 and in the gas phase. The main characteristics of the ring-chain equilibria expressed by the variable SigmaRA% of the ring and of the chain form proved to be a strong dependence on the nature of the substituents on C-2 and C-4. The results in the gas phase are compared with those in CDCl3.