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1.
Dr. Christopher R. Opie Dr. Hidetoshi Noda Prof. Dr. Masakatsu Shibasaki Dr. Naoya Kumagai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(18):4648-4653
The B3NO2 six-membered heterocycle (1,3-dioxa-5-aza-2,4,6-triborinane=DATB), comprising three different non-carbon period 2 elements, has been recently demonstrated to be a powerful catalyst for dehydrative condensation of carboxylic acids and amines. The tedious synthesis of DATB, however, has significantly diminished its utility as a catalyst, and thus the inherent chemical properties of the ring system have remained virtually unexplored. Here, a general and facile synthetic strategy that harnesses a pyrimidine-containing scaffold for the reliable installation of boron atoms is disclosed, giving rise to a series of Pym-DATBs from inexpensive materials in a modular fashion. The identification of a soluble Pym-DATB derivative allowed for the investigation of the dynamic nature of the B3NO2 ring system, revealing differential ring-closing and -opening behaviors depending on the medium. Readily accessible Pym-DATBs proved their utility as efficient catalysts for dehydrative amidation with broad substrate scope and functional-group tolerance, offering a general and practical catalytic alternative to reagent-driven amidation. 相似文献
2.
Dr. Xinxin Tang Dr. Hidetoshi Noda Prof. Dr. Masakatsu Shibasaki 《Angewandte Chemie (International ed. in English)》2023,62(51):e202311027
The exponential proliferation of conformers makes it impossible to examine the entire population in most systems. Controlling conformational ensembles is thus pivotal in many areas of chemistry. Rh2(esp)2, a dicarboxylate-derived paddlewheel rhodium complex, is one of the most effective catalysts for nitrene chemistry. Its enormous success has led to preparing many analogous complexes. However, there has been little consideration for the conformational dynamics of the parent catalyst. Herein, we report a new ligand modification principle that prevents conformer interconversion. The resulting complex comprises two isolable conformers, whose structures have been determined by X-ray diffraction. Combined experimental and computational data has revealed similarities and dissimilarities between the conformationally confined and parent complexes. Three model cases have demonstrated the utility of conformational fixation in the development of stereoselective catalysts for nitrene transfer reactions. The design principle described in this study can be combined with other established modification strategies, serving as a springboard for further advancement of the chemistry of paddlewheel metal complexes. 相似文献
3.
Dr. Akihiro Takada Hiroaki Fujiwara Dr. Kenji Sugimoto Dr. Hirofumi Ueda Prof. Dr. Hidetoshi Tokuyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(46):16400-16403
The total synthesis of (?)‐isoschizogamine was accomplished, featuring the construction of the quaternary carbon center by the modified Johnson–Claisen rearrangement in basic media and the facile assembly of the key tetracyclic quinolone intermediate through a cascade cyclization. The characteristic cyclic aminal was constructed by late‐stage C?H functionalization at the position adjacent to the lactam nitrogen using a combination of CrO3 and nBu4NIO4 and subsequent Bi(OTf)3‐mediated cyclization. 相似文献
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Hidetoshi Shinada 《Optical Review》2016,23(5):765-769
Digital printing systems recorded on films or computer to plates (CTPs) have been required to improve their productivity and image quality. Under the circumstance, a printing technology of the multi-beam laser scanning for the drum capstan system, which is almost the same as optics configuration as the flat bed system, was developed using a newly developed multi-frequency acousto–optic modulator (AOM) as a key device instead of ultra-fast scanning devices toward a main scan direction. The multi-frequency AOM was developed with phased array-type transducers, achieving a wider bandwidth of over 160 MHz. The design consisted of a simultaneous three beams generation with interlace scan to avoid the beat effect by adjacent Doppler-shifted beams, which consequently attained the fastest recording speed of 5.0 mm/s compared with 2.0–3.0 mm/s of existing systems in those days. Furthermore, a couple of critical parameters of the multi-frequency AOM are studied, for example, a treatment of third-order intermodulation and also beat effect in connection with photosensitive media. As a result, the necessity of interlaces scanning to obtain good image quality without beat effect and also to allow a lower laser power to apply is proposed. 相似文献
6.
Motohiro Aiba Takahiro Tokuyama Susumu Baba Hidetoshi Matsumoto Hiroki Tomioka Tomoya Higashihara Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》2014,52(9):1275-1281
A new concept for the method to provide semipermeability in ultrathin and single‐component wholly aromatic polyamide membranes has been developed for the first time. It was found that water molecules could permeate through the membrane prepared not from polyamides containing flexible ether, bulky binaphthyl, or fluorene rigid units, but one with carboxylic acid groups under a reverse osmosis mode. However, the enhancement of water transport properties by introducing the hydrophilic group of polyamide was not substantial. Therefore, polyamide membranes were prepared from the solution containing aqueous additives in order to weaken hydrogen bonds between polymer chains and thereby to suppress the aggregation of the polymer chains. As a result, water flux was dramatically improved with slightly improved NaCl rejection. Our analyses based on attenuated total reflectance Fourier transform infrared spectroscopy and solid‐state carbon polarization and magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy confirmed that the aggregation of polymer chains due to the hydrogen bonds among the amide linkages was suppressed by the co‐ordination of the aqueous additives to the amide linkage. The state of water in the membranes analyzed by differential scanning calorimetry also supported the formation of pores. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1275–1281 相似文献
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Defect turbulence described by the one-dimensional complex Ginzburg–Landau equation is investigated and analyzed via a birth–death process of the local structures composed of defects, holes, and modulated amplitude waves (MAWs). All the number statistics of each local structure, in its stationary state, are subjected to Poisson statistics. In addition, the probability density functions of interarrival times of defects, lifetimes of holes, and MAWs show the existence of long-memory and some characteristic time scales caused by zigzag motions of oscillating traveling holes. The corresponding stochastic process for these observations is fully described by a non-Markovian master equation. 相似文献
10.
Prof. Takanori Suzuki Yuto Sakano Dr. Tomohiro Iwai Dr. Shinichi Iwashita Dr. Youhei Miura Dr. Ryo Katoono Prof. Hidetoshi Kawai Prof. Kenshu Fujiwara Prof. Yasushi Tsuji Prof. Takanori Fukushima 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):117-123
When two benzene rings are fused to a tetraaryl‐o‐quinodimethane skeleton, sterically hindered helical molecules 1 acquire a high thermodynamic stability. Because the tetraarylbutadiene subunit contains electron‐donating alkoxy groups, 1 undergo reversible two‐electron oxidation to 2 2+, which can be isolated as deeply colored stable salts. Intramolecular transfer of the point chirality (e.g., sec‐butyl) on the aryl groups to helicity induces a diastereomeric preference in dications 2 b 2+ and 2 c 2+, which represents an efficient method for enhancing circular‐dichroism signals. Thus, those redox pairs can serve as new electrochiroptical response systems. X‐ray analysis of dication 2 2+ revealed π–π stacking interaction of the diarylmethylium moieties, which is also present in solution. The stacking geometry is the key contributor to the chirosolvatochromic response. 相似文献