Nickel-catalyzed [4+3] cycloaddition of ethyl cyclopropylideneacetate and 1,3-dienes

The [4+3] cycloaddition of ethyl cyclopropylideneacetate (1) with 1,3-dienes proceeded in the presence of Ni(cod)₂-TOPP (tri-o-biphenylyl phosphite). The reaction provided a new method for the synthesis of cycloheptene derivatives. The mechanism of the reaction was proposed.     

Structural Insights into Rice Straw Pretreated by Hot-Compressed Water in Relation to Enzymatic Hydrolysis

Pretreatment-induced structural alteration is critical in influencing the rate and extent of enzymatic saccharification of lignocellulosic biomass. The present work has investigated structural features of rice straw pretreated by hot-compressed water (HCW) from 140 to 240 °C for 10 or 30 min and enzymatic hydrolysis profiles of pretreated rice straw. Compositional profiles of pretreated rice straw were examined to offer the basis for structural changes. The wide-angle X-ray diffraction analysis revealed possible modification in crystalline microstructure of cellulose and the severity-dependent variation of crystallinity. The specific surface area (SSA) of pretreated samples was able to achieve more than 10-fold of that of the raw material and was in linear relationship with the removal of acetyl groups and xylan. The glucose yield by enzymatic hydrolysis of pretreated materials correlated linearly with the SSA increase and the dissolution of acetyl and xylan. A quantitatively intrinsic relationship was suggested to exist between enzymatic hydrolysis and the extraction of hemicellulose components in hydrothermally treated rice straw, and SSA was considered one important structural parameter signaling the efficiency of enzymatic digestibility in HCW-treated materials in which hemicellulose removal and lignin redistribution happened.     

Strategy for synthesis of the isoleucine conjugate of epi-jasmonic acid

The TES ether of 2-((1R,2S,3R)-3-hydroxy-2-((Z)-pent-2-enyl)cyclopentyl)acetic acid (5, equal to the reduction product of epi-jasmonic acid) derived from (1R,4S)-4-hydroxycyclopent-2-enyl acetate (19) in 13 steps was activated by using isobutyl chloroformate and was subjected to condensation with isoleucine at room temperature for 48 h. The product was desilylated and oxidized to the isoleucine conjugate of epi-jasmonic acid in 68% yield over three steps. Similarly, allo-isoleucine conjugate of epi-jasmonic acid and three isoleucine conjugates of ent-epi-jasmonic acid, jasmonic acid, and ent-jasmonic acid were synthesized.     

Fabrication of novel layer-by-layer assembly films composed of poly(lactic acid) and polylysine through cation-dipole interactions

Novel layer-by-layer (LbL) assembly films composed of poly( L-lysine) (PLL) and poly( D-lactic acid) (PDLA) were prepared by the alternate immersion of a gold substrate into an aqueous PLL solution and an acetonitrile solution of PDLA. The formation of the LbL assembly film was confirmed by quartz crystal microbalance (QCM) analysis, atomic force microscopy observation, and attenuated total reflection Fourier transform infrared spectroscopy measurement. The driving force responsible for the LbL assembly was determined by investigating the formation behavior of the LbL assembly under various conditions. The formation of the LbL assembly was not affected either by the stereochemistry of polylysine and poly(lactic acid) or by the addition of urea, which is known to inhibit hydrogen bonding interaction between polymers, into the aqueous PLL solution. The LbL assembly was also formed by the combination of PDLA and polycations other than polylysine, such as poly(diallyldimethylammonium chloride). On the other hand, the combination of PDLA and any polyanions such as poly(styrene sulfonate sodium salt) produced little corresponding LbL assembly. The increase in positive charge on the amino nitrogen atom of PLL enhanced the LbL assembly. These results suggest that the LbL assembly film composed of PLL and PDLA was fabricated by cation-dipole interactions between the positive charge on the amino nitrogen atom of PLL and the lone pairs of the carbonyl oxygen atom of PDLA.     

Generation and detection of the radical cation and the dication derived from 4,9‐diethyl[1,4]dihydrodithiino[5,6‐f]benzotrithiole and its 5‐oxide

4,9‐Diethyl[1,4]dihydrodithiino[5,6‐f]benzotrithiole (DTBT) gave a radical cation, DTBT(•+), and a dication, DTBT(2+), on treatment with a single‐electron oxidizing reagent. Both compounds showed an ESR signal, whereas the dication, generated by this procedure, was silent for ¹H NMR. Hydrolysis of DTBT(2+) gave DTBT 1‐oxide (DTBT 1‐O) and 2‐oxide (DTBT 2‐O) together with DTBT and a mixture of several dioxides. A singlet‐state dication, DTBT(2+)‐S, which was generated upon treatment of DTBT 5‐oxide (DTBT 5‐O) with concentrated D₂SO₄, was detected by ¹H and ¹³C NMR. After 20 h, the NMR signals disappeared while the solution was active for ESR. The results suggest that (i) a species generated from DTBT by oxidation with the single‐electron oxidizing reagent is a triplet‐state dication, DTBT(2+)‐T, and (ii) DTBT(2+)‐S, initially generated, gradually isomerizes to DTBT(2+)‐T in the solution, and DTBT(2+)‐T forms a partial spin pair. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:394–401, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20445     

Synthesis and properties of a chelating resin containing triazolethiol groups

A macroreticular poly(acrylic acid)-based resin with triazolethiol as the functional group has been synthesized. The stability of the resin in acidic media and the behaviour in sorption and desorption of various metal ions have been investigated and compared with those of the acylthiosemicarbazide resin which is an intermediate in synthesis of the triazolethiol resin. Both resins show high affinity for copper(II) silver, cadmium and mercury(II), and high selectivity for silver and mercury(II) at low pH (1–2), and even at pH 7 if EDTA is present. The triazolethiol resin sorbs metal ions faster than the acylthiosemicarbazide resin does and sorbs mercury(II) from high concentrations of acids and neutral salt solutions. This resin has been applied to the concentration of silver and mercury(II) from sea-water samples by column operation.     

Novel rearrangement of twisted 2,4-di-alkyl 2-trans-4-trans pentadienals: An approach to cyclopentenones based on molecular mechanical consideration

Rearrangement of 2,4-di-$\text{trans}$-pentadienals $\text{IVa-d}$ was described as a consequence of the successive alkyl substitutions on the C-2 and C-4 positions. ¹H-FT nmr spectroscopy suggested that the reaction involves ketene $\text{VIII}$ as an intermediate.     

Catalyst‐free synthesis of polyorganosiloxanes by high temperature and pressure water. II. Understanding of the reaction process

A catalyst‐free polysiloxane synthetic process that uses high temperature and pressure water for the hydrolysis and subsequent polycondensation of phenyltrimethoxysilane was studied in detail to gain insights into the reaction mechanism. It was suggested that this process is essentially composed of two stages: (1) oligomerization of phenyltrimethoxysilane yielding low‐molecular weight species with high contents of silanol and methoxy groups and (2) polycondensation of the oligomers yielding high‐molecular weight species. The use of a preformed oligosiloxane as a starting material was informative to understand the polycondensation stage. A modified synthetic process in which a stop valve was introduced to control the internal pressure was developed based on the understanding of the present process. This modified process enabled a two‐stage reaction resulting in a discernible increase of the molecular weight of polysiloxane. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2656–2663, 2009