Enantioselective total synthesis of a natural hydrocarbazolone alkaloid,identification of its stereochemistry,and revision of its spectroscopic data

The natural hydrocarbazolone alkaloid (1R,2R,3R)-3-hydroxy-1,2-dimethyl-1,2,3,9-tetrahydro-4H-carbazol-4-one has been synthesized in a catalytic and enantioselective manner. A key hydrocarbazole derivative was constructed by the holmium-catalyzed Diels-Alder reaction of (silyloxyvinyl)indole as the diene. Total synthesis of the natural product clarified the ambiguity in the spectroscopic data reported for natural products.     

Synthesis and radical ring‐opening polymerization of vinylcyclopropanes derived from amino acids with hydrophobic moieties

Six 1,1‐disubstituted vinylcyclopropanes (VCP) were synthesized from glycine and amino acids bearing hydrophobic moieties, l ‐alanine, l ‐valine, l ‐leucine, l ‐isoleucine, and l ‐phenylalanine. These VCP derivatives efficiently underwent radical ring‐opening polymerization to afford the corresponding polymers bearing trans‐vinylene moiety in the main chains and the amino acid‐derived chiral moieties in the side chains. The polymers were film‐formable, and in the films of polymers bearing the glycine‐ and alanine‐derived side chains, presence of hydrogen bonding was confirmed by IR analysis. Thermogravimetric analysis of the polymers revealed that the temperatures of 5% weight loss were higher than 300 °C. Differential scanning calorimetry clarified that the polymers were amorphous ones showing glass transition temperatures in a range of 48–80 °C. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3996–4002     

Physical properties of diblock methylcellulose derivatives with regioselective functionalization patterns: First direct evidence that a sequence of 2,3,6‐tri‐O‐methyl‐glucopyranosyl units causes thermoreversible gelation of methylcellulose

This article describes detailed structure‐property relationships of 5 regioselectively methylated celluloses and 10 diblock cellulose derivatives with regioselective functionalization patterns: methyl 2,3,6‐tri‐O‐ ( 1 , 236MC), methyl 2,3‐di‐O‐ ( 2 , 23MC), methyl 2,6‐di‐O‐ ( 3 , 26MC), methyl 3‐O‐ ( 4 , 3MC), methyl 6‐O‐methyl‐cellulosides ( 5 , 6MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,3,6‐tri‐O‐methyl‐ ( 6 , G‐236MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,3‐di‐O‐methyl‐ ( 7 , G‐23MC), methyl β‐D‐glucopyranosyl‐(1→4)‐2,6‐di‐O‐methyl‐ ( 8 , G‐26MC), methyl β‐D‐glucopyranosyl‐(1→4)‐3‐O‐methyl‐ ( 9 , G‐3MC), methyl β‐D‐glucopyranosyl‐(1→4)‐6‐O‐methyl‐ ( 10 , G‐6MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,3,6‐tri‐O‐methyl‐ ( 11 , GG‐236MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,3‐di‐O‐methyl‐ ( 12 , GG‐23MC), methyl β‐D‐glucopy‐ranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐2,6‐di‐O‐methyl‐ ( 13 , GG‐26MC), methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐3‐O‐methyl‐ ( 14 , GG‐3MC), and methyl β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐6‐O‐methyl‐cellulosides ( 15 , GG‐6MC). Surface tension, differential scanning calorimetry, fluorescence, and dynamic light scattering measurements of aqueous solutions of compounds 1 – 15 revealed that there was no relationship between aggregation behaviors and gel formation, gelation occurred only when the hydrophobic environments formed by hydrophobic interactions between the sequences of 2,3,6‐tri‐O‐methyl‐glucopyranosyl units upon heating. The diblock structure consisting of cellobiosyl block and approx. ten 2,3,6‐tri‐O‐methyl‐glucopyranosyl units was of crucial importance for thermoreversible gelation of methylcellulose. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1539–1546, 2011     

Preparation of poly(acrylic acid)‐b‐polystyrene by two‐step atom transfer radical polymerization in supercritical carbon dioxide

It is known that it is difficult to polymerize carboxylic acid‐based monomer by atom transfer radical polymerization (ATRP) in polar solvents due to the protonation of ligand caused by acidic dissociation of the monomer. In this study, precipitation reverse ATRP of acrylic acid (AA) was carried out in supercritical carbon dioxide (scCO₂), which is a nonpolar solvent to dissolve transition metal complexes, at 30 MPa and 45 °C. The polymerization proceeded smoothly and the conversion reached 86% for 3 h. After vending of scCO₂, a dry poly(acrylic acid) (PAA) powder was obtained. Weight‐average molecular weight and polydispersity of the methylated PAA, which were measured by gel‐permeation chromatography after methyl esterification, were 3.5 × 10⁴ and 2.07, respectively, indicating that the precipitation reverse ATRP proceeded with a bad control manner. However, chain extension of the methylated PAA with styrene was possible by ATRP in a bulk system. Moreover, PAA‐b‐polystyrene was successfully prepared in scCO₂ directly by two‐step ATRP, although its molecular weight distribution was broad. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Wavy texture in pressure-driven startup flows of liquid crystalline polymer solutions through a slit cell: effects of polymer concentration and solution temperature

Dependences of wavy texture on polymer concentration and solution temperature were examined using aqueous solutions of hydroxypropylcellulose (HPC). The phase of aqueous solution of HPC varied from an isotropic (I) system to a liquid crystalline (LC) one through a biphasic (I+LC, LC+I) system with increasing the HPC concentration and/or decreasing the solution temperature. The wavy texture emerged not only in the LC system but also in the LC+I system. Furthermore, induction time of wavy texture was evaluated in terms of apparent shear strain. It is suggested that polydomain structures included in liquid crystalline systems and droplets of isotropic phase in biphasic systems affect the initial stage of emergence of wavy texture at low shear rates.     

Tomographic reconstruction of damage images in hollow cylinders using Lamb waves

Lamb wave tomography (LWT) is a potential and efficient technique for non-destructive tomographic reconstruction of damage images in structural components or materials. A two-stage inverse algorithm proposed by the authors for quickly reconstructing the damage images was applied to hollow cylinders. An aluminum hollow cylinder with an internal surface pit and a Carbon Fiber Reinforced Plastic (CFRP) laminated hollow cylinder with an artificial internal surface damage were used to validate the proposed method. The results show that the present method is capable of successfully reconstructing the images of the above damages in a larger inspection area with much less experimental data compared to some conventional ultrasonic tomography techniques.