Search Results (5)

An unreported and unusual nor-neolignan dimer, namely bis((5-allyl-2-(benzo[d][1,3]dioxol-5-yl)benzofuran-7-yl)oxy)methane (1), was isolated from the bark-derived chloroform extract of Magnolia grandiflora L. Compound 1 was structurally elucidated through the detailed analysis of the spectroscopic data (one- and two-dimensional nuclear magnetic resonance, infrared, and high-resolution mass spectrometry). The effect of compound 1 on the mycelial growth of Fusarium oxysporum was also determined, affording moderate antifungal activity. Full article

The regioselective synthesis of novel functionalized condensed organochalcogen compounds by chalcogenocyclofunctionalization reactions based on chalcogen halides and the natural products thymol and carvacrol has been developed. The reactions of selenium dibromide with allyl thymol and allyl carvacrol proceeded in methylene chloride at room temperature in the presence of NaHCO₃ affording bis[(7-isopropyl-4-methyl-2,3-dihydro-1-benzofuran-2-yl)methyl] and bis[(4-isopropyl-7-methyl-2,3-dihydro-1-benzofuran-2-yl)methyl] selenides in 90–92% yield. Similar sulfides were obtained in 70–72% yields by the reaction of sulfur dichloride in chloroform under reflux. Trihalotellanes containing the same organic moieties were synthesized from allyl thymol, allyl carvacrol and tellurium tetrachloride or tetrabromide in quantitative yields. Corresponding functionalized ditellurides were prepared in 91–92% yields by the reduction of the trichlorotellanes with sodium metabisulfite in two-phase solvent system. The comparison of reactivity of sulfur, selenium and tellurium halides in chalcogenocyclofunctionalization and distinguishing features of each reaction were discussed. Full article

Through reducing the system InCl₃-Li-DTBB(cat.) in THF at room temperature and in the absence of any additives or anti-caking ligand, we have synthesized indium nanoparticles (InNPs) of about 4 nm. The catalyst was employed in the allylation of carbonyl compounds, giving excellent yields of the corresponding homoallylic alcohols. We have established that the reaction products come from a γ-coupling via a six members cyclic transition state, type Zimmerman–Traxler. Relative to the selectivity, the allylation with crotyl bromide of ortho substituted benzaldehydes (e.g., o-NO₂, o-OMe, o-Cl, o-CF₃) showed syn selectivity. With the aim to improve the mentioned selectivity, we synthetized o-ⁱPrO-benzaldehyde, and evaluated the reaction with crotyl bromide and InNPs. The homoallylic alcohol 1-(2-isopropoxyphenyl)-2-methylbut-3-en-1-ol was obtained almost quantitatively after 1h as a mixture of the syn- and anti- isomers. The relationship observed by ¹H-RMN was 75:25, but we did not know if the syn-isomer was the dominant because the product has not been reported in the scientific literature. Based on this, and in order to determinate which 1H-NMR signals correspond to each isomer, we started computational theoretical and NMR studies. The initial conformational analysis was performed using the semiempirical PM3 method, then we work with the B3LYP functional, applying the 6-31+G* basis set and the solvent effect (chloroform) was evaluated with the PCM model as implemented in Gaussian09. So, we found thirteen low-energy conformations for the syn-diastereomer and six low-energy conformations for the anti-diastereomer. On the other hand, we have carried out NMR experiments such as ¹H, ¹³C, HSQC, to assign the signals of each diastereomer; and experiments such as NOESY, selective NOE, JRes, homo- and hetero-nuclear J-coupled and J-decoupling, to be able to measure coupling constants and establish the structure of each diastereomer. Full article

At 25.0 °C the specific rates of solvolysis for allyl and vinyl chloroformates have been determined in a wide mix of pure and aqueous organic mixtures. In all the solvents studied, vinyl chloroformate was found to react significantly faster than allyl chloroformate. Multiple correlation analyses of these rates are completed using the extended (two-term) Grunwald-Winstein equation with incorporation of literature values for solvent nucleophilicity (N_T) and solvent ionizing power (Y_Cl). Both substrates were found to solvolyze by similar dual bimolecular carbonyl-addition and unimolecular ionization channels, each heavily dependent upon the solvents nucleophilicity and ionizing ability. Full article

Starting from 2-(triphenylsilyl)ethanol a new oxycarbonyl protecting group cleavable by fluoride ion induced Peterson-elimination has been developed. Known 2-(triphenylsilyl)ethanol has been prepared from commercially available triphenylvinyl-silane by a hydroboration-oxidation sequence using the sterically hindered borane reagent 9-BBN. The silyl alcohol was subsequently transformed into its chloroformate, imidazolylcarboxylic acid ester and p-nitrophenyl carbonate and used in standard protocols for the formation of carbamates and carbonates. The Tpseoc group proved to be highly resistant against acidic conditions applied in removal of tert-butyl esters and the t-Boc-group. It also withstood catalytic hydrogenation, treatment with morpholine, methylhydrazine and Pd-reagents/allyl-scavanger combinations, conditions required to cleave Cbz-, Fmoc-, phthalimide- and Alloc-groups. The Tpseoc-group is cleaved upon treatment with TBAF/CsF at 0 °C or r.t. with cleavage times reaching from < 10 min. to 24 h. Its orthogonality, ease of cleavage and UV-detectability makes the Tpseoc-group a promising alternative to other widely used silicon based amine protecting groups like the Teoc- and SES-groups. Full article