Synthesis of 1-haloethenamides from ynamide through halotrimethylsilane-mediated hydrohalogenation

A convenient synthesis of 1-haloethenamides has been achieved by utilizing halotrimethylsilane (TMSX, X = Cl, Br, I) and water. Halotrimethylsilane in 1 M CH₂Cl₂ solution functions as a halogen source of the in situ generated HX, and the HX added to the terminal triple bonds of ynamides in Markovnikov fashion.     

Rhodium-Catalyzed [2+1+2+1] Cycloaddition of Benzoic Acids with Diynes through Decarboxylation and C≡C Triple Bond Cleavage

It has been established that an electron-deficient cyclopentadienyl rhodium(III) (Cp^ERh^III) complex catalyzes the oxidative and decarboxylative [2+1+2+1] cycloaddition of benzoic acids with diynes through C≡C triple bond cleavage, leading to fused naphthalenes. This cyclotrimerization is initiated by directed ortho C−H bond cleavage of a benzoic acid, and the subsequent regioselective alkyne insertion and decarboxylation produce a five-membered rhodacycle. The electron-deficient nature of the Cp^ERh^III complex promotes reductive elimination giving a cyclobutadiene–rhodium(I) complex rather than the second intermolecular alkyne insertion. The oxidative addition of the thus generated cyclobutadiene to rhodium(I) (formal C≡C triple bond cleavage) followed by the second intramolecular alkyne insertion and reductive elimination give the corresponding [2+1+2+1] cycloaddition product. The synthetic utility of the present [2+1+2+1] cycloaddition was demonstrated in the facile synthesis of a donor–acceptor [5]helicene and a hemi-hexabenzocoronene by a combination with the chemoselective Scholl reaction.     

Rhodium(I)-catalyzed direct carboxylation of arenes with CO2 via chelation-assisted C-H bond activation

Rh-catalyzed direct carboxylation of unactivated aryl C-H bond under atmospheric pressure of carbon dioxide was realized via chelation-assisted C-H activation for the first time. Variously substituted and functionalized 2-arylpyridines and 1-arylpyrazoles underwent the carboxylation in the presence of the rhodium catalyst and a stoichiometric methylating reagent, AlMe(2)(OMe), to give carboxylated products in good yields. The catalysis is proposed to consist of methylrhodium(I) species as the key intermediate, which undergoes C-H activation to afford rhodium(III), followed by reductive elimination of methane to give nucleophilic arylrhodium(I). This approach demonstrates promising application of C-H bond activation strategy in the field of carbon dioxide fixation.     

Inclusion of Two Different Guest Molecules within a Rationally Designed Macrocyclic Boronic Ester in Organic Solvent

The inclusion of two different guest molecules in a macrocyclic boronic ester in organic solvent utilizing only π‐stacking interactions has been successfully realized. For this purpose, a new tetrol which has an appropriate distance between two 1,2‐diol units for the inclusion of two aromatic molecules is designed and synthesized. Simple mixing of the new tetrol with 2,7‐pyrenediboronic acid in the presence of pyrene‐4,5‐quinone efficiently affords the desired macrocyclic boronic ester, which is found by ¹H NMR spectroscopy, ESI‐MS, and isothermal titration calorimetry studies to include one molecule each of a dinitronaphthalimide derivative and pyrene. Furthermore, inclusion of two planar molecules within the macrocyclic boronic ester is revealed by X‐ray analysis.     

Determination of cadmium in river water by electrothermal atomic absorption spectrometry after internal standardization-assisted rapid coprecipitation with lanthanum phosphate.

Cadmium ranging from 1 - 8 ng could be coprecipitated quantitatively with lanthanum phosphate at pH 5 - 6 from up to 200 mL of river water samples spiked with 5 microg of indium as an internal standard. Cadmium and indium coprecipitated were measured by using electrothermal atomic absorption spectrometry. The cadmium content in the original sample solution could be determined by internal standardization with indium. Since complete collection of the precipitate and strict adjustment of the volume of the final solution after coprecipitation are not required in this method, the precipitate could be collected by using decantation and centrifugation, and then dissolved with 1 mL of about 2.4 mol L(-1) nitric acid. The proposed method is simple and rapid, and enrichment close to 200-times can be attained; the detection limit (3sigma, n = 6) was 0.63 ng L(-1) in 200 mL of the sample solution.