Cycloaddition reactions of 2-vinylthiophen

Cycloaddition reactions between 2-vinylthiophen and the dienophiles maleic anhydride, dimethyl acetylenedicarboxylate,' methyl propiolate, and methyl acrylate, are reported. Products include simple benzo[b]thiophen carboxylates (6, 13, 17) and reduced derivatives (3, 4, 18). The acetylenic dienophiles also gave a dihydrobenzthienyl-acrylate (16) or -fumarate (11), and the dithienylcyclohexene esters (7) and (14).     

Screening of homocysteine from newborn blood spots by high-performance liquid chromatography with coulometric array detection

Homocystinuria, due to a deficiency of cystationine-beta-synthase, refers to the rare inborn error of the metabolism of homocysteine. The identification and prompt treatment of homocystinuria during the neonatal period can prevent or greatly reduce the severity of the clinical consequences. We report a new method for homocystinuria diagnosis from dried blood spots on newborn screening cards, based on high-performance liquid chromatography with electrochemical coulometric array detection. This method shows an excellent linearity (y=10.36x+0.04; r=0.999), precision (RSDs ranged from 2.7 to 5.8%), recovery (87%) and appears to be a cost-effective approach, being simple, rapid, sensitive and cheap.     

Enantioselective epoxidation of alkenes catalyzed by 2-fluoro-N-carbethoxytropinone and related tropinone derivatives

Several alpha-substituted N-carbethoxytropinones have been evaluated as catalysts for asymmetric epoxidation of alkenes with Oxone, via a dioxirane intermediate. alpha-Fluoro-N-carbethoxytropinone (2) has been studied in detail and is an efficient catalyst which does not suffer from Baeyer-Villiger decomposition and can be used in relatively low loadings. This ketone was prepared in enantiomerically pure form using chiral base desymmetrization of N-carbethoxytropinone. Asymmetric epoxidation catalyzed by 2 affords epoxides with up to 83% ee. Among other derivatives tested, the alpha-acetoxy derivative 7 affords the highest enantioselectivities.     

Synthesis of 4-hetaryl-5,6-(2,5-dimethyl-3-thienyl)-2-phenyl-4h-thiazines and investigation of their photochromism

The polar [4+2] cycloaddition reaction of 1,2-bis(2,5-dimethyl-3-thienyl)acetylene with thiobenzamide and certain aldehydes of the thiophene and furan series catalyzed by boron trifluoride etherate gives the corresponding 4-hetaryl-5,6-di(2,5-dimethyl-3-thienyl)-2-phenyl-4H-1,3-thiazines. The photochromic properties of the products have been studied.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 100–106, January, 2005.     

Synthesis and x-ray crystal structure of the TiMgCl5(OOCCH2Cl) · (ClCH2COOC2H5)3 Adduct

The synthesis of the TiMgCl₅(OOCCH₂Cl) · (ClCH₂COOC₂H₅)₃ adduct, obtained by reacting TiCl₄ with a solution of MgCl₂ in dry ClCH₂COOC₂H₅, is reported together with its molecular and crystal structure as determined by x-ray diffraction. The structure was solved by direct and Fourier methods and refined by least-squares techniques to R = 0.057 for 1318 independent observed reflections. Crystals are monoclinic, space-group P2₁/c, with 4 formula units in a unit-cell of dimensions a = 10.480(4), b = 19.641(9), c = 16.597(6) Å, β = 120.21(5)°. The titanium(IV) atom is octahedrally coordinated by five chlorine atoms and an oxygen atom of a OOCCH₂Cl residue. The magnesium atom is similarly coordinated by two chlorine atoms, the carbonyl oxygen atoms of three ClCH₂COOC₂H₅ molecules and an oxygen atom of the OOCCH₂Cl residue. The two octahedra share an edge by a double chlorine bridge between the magnesium and the titanium atoms and are also connected by the COO group of the OOCCH₂Cl residue. Changes in the configurations and dimensions with respect to the free acceptor and donor molecules are discussed.     

Paired electrosynthesis of cyanoacetic acid

Cyanoacetic acid is formed by cathodic reduction of CO(2) and anodic oxidation of the tetraalkylammonium salt anion; the process is conduced in acetonitrile using a divided cell with a medium porosity glass-frit diaphragm. A mechanism for this paired electrochemical reaction is proposed.     

Electrochemical dimerization of phenacyl bromides N-acylhydrazones—a new way to 1-N-acylamino-2,5-diaryl-pyrroles

Cathodic reduction of phenacyl bromides N-acyl hydrazones lead to dimeric 1,4-diaryl-1,4-butanedione di-N-acylhydrazones, which give the corresponding 1-N-acylamino-2,5-diarylpyrroles in good yields.     

Photochromic dihetarylethenes. 13. Optimization of conditions for the acylation of 2,5-dimethylthiophene with squaric acid dichloride

The conditions for acylation of 2,5-dimethylthiophene with squaric acid dichloride were optimized, and 3,4-bis(2,5-dimethylthiophen-3-yl)cyclobut-3-ene-1,2-dione was obtained in good yield. X-ray diffraction analysis demonstrated that the by-product has the structure of 1a,1b-dichloro-5-(2,5-dimethylthiophen-3-yl)-3-hydroxy-4,5a-dimethyl-1b,4a,5,5a-tetrahydro-1aH-1-thiacyclopropa[a]pentalen-2-one.     

Spectroscopic and structural impact of a stem base-pair change in DNA hairpins: GTTC-ACA-GAAC versus GTAC-ACA-GTAC

Successive investigations over the last decade have revealed and confirmed a stable loop closure in a family of d-[GTAC-5Pur6N7N-GTAC] hairpins, where 5Pur6N7N is a AAA, GAG and AXC loop (X being any nucleotide). The trinucleotide loop is characterized by a well defined 5Pur-7N mispairing mode, and by upfield chemical shifts for three sugar protons of the apical nucleotide 6N. The GTTC-ACA-GAAC DNA hairpin, of interest for its likely involvement in Vibrio cholerae genome mutations, has now been investigated. The GTAC-ACA-GTAC DNA hairpin has also been studied because it is intermediate between the other structures, as it contains the loop of the hairpin under consideration and the stem of the above family. The two hairpins with the ACA loop are stable. They show the same mispairing mode and similar upfield shifts as the previous family, but GTTC-ACA-GAAC seems to be slightly less compact than any other. GTTC-ACA-GAAC is remarkable in that it exhibits a B(II) character for the phosphate-ester conformation at 8Gp9A, together with a swing of the upper hairpin into the major groove that, in particular, brings 6CH1' roughly as close to 7AH2 as to 6CH6. These unexpected structural features are qualitatively deduced from (1)H and (31)P NMR spectra, and confirmed by Raman spectroscopy. This comparative study shows that not only the loop sequence but also the stem sequence may control hairpin structures.     

Unusual reaction of α-diketones of the indole series with hydrazine

Symmetrical and unsymmetrical α-diketones of the indole series were synthesized by the Friedel-Crafts reaction of 3-indolylglyoxyl chlorides with heterocycles. A nonconventional reaction of N-unsubstituted diketones with hydrazine producing 3H-pyrazolo[3,4-c]quinoline derivatives was found. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 862–866, May, 2006.