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991.
Stavroula I. Sampani Dr. Victor Zdorichenko Jack Devonport Gioia Rossini Dr. Matthew C. Leech Dr. Kevin Lam Prof. Brian Cox Dr. Alaa Abdul-Sada Dr. Alfredo Vargas Dr. George E. Kostakis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(13):4394-4400
The hybrid bidentate 1-(2-pyridyl)benzotriazole (pyb) ligand was introduced into 3d transition metal catalysis. Specifically, [CuII(OTf)2(pyb)2] ⋅ 2 CH3CN ( 1 ) enables the synthesis of a wide range of propargylamines by the A3 coupling reaction at room temperature in the absence of additives. Experimental and high-level theoretical calculations suggest that the bridging N atom of the ligand imposes exclusive trans coordination at Cu and allows ligand rotation, while the N atom of the pyridine group modulates charge distribution and flux, and thus orchestrates structural and electronic precatalyst control permitting alkyne binding with simultaneous activation of the C−H bond via a transient CuI species. 相似文献
992.
Positivity - In this paper set optimization problems with three types of set order relations are concerned. We introduce various types of Levitin–Polyak (LP) well-posedness for set... 相似文献
993.
Aaron J. Day Joel H. Z. Lee Quang D. Phan Hiu C. Lam Adam Ametovski Christopher J. Sumby Stephen G. Bell Jonathan H. George 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(5):1441-1445
The first total synthesis of bruceol has been achieved using a biomimetic cascade cyclization initiated by a stereoselective Jacobsen–Katsuki epoxidation (and kinetic resolution) of racemic protobruceol‐I. A bacterial cytochrome P450 monooxygenase was also found to catalyze the conversion of protobruceol‐I into bruceol. The first full analysis of the NMR data of natural bruceol suggested that “isobruceol” was a previously unrecognized natural product also isolated from Philotheca brucei. This was confirmed by the re‐isolation, synthesis, and X‐ray analysis of isobruceol. In total, eight stereoisomers and structural isomers of bruceol have been synthesized in a highly divergent approach. 相似文献
994.
Furans bearing epoxy enolsilane units linked by a nitrogen heteroatom tether undergo intramolecular (4 + 3) cycloadditions to generate bis-heteroatomic polycyclic adducts having piperidine moieties in their frameworks. The cycloadducts, ultimately derived from furfural, a renewal chemical feedstock, are obtained with up to 4:1 dr and with ee retained from the epoxide. 相似文献
995.
996.
997.
Chun‐Wei Chang Chia‐Hui Wu Mei‐Huei Lin Pin‐Hsuan Liao Chun‐Chi Chang Hsiao‐Han Chuang Su‐Ching Lin Sarah Lam Ved Prakash Verma Chao‐Ping Hsu Cheng‐Chung Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(47):16931-16935
Stereocontrolled chemical glycosylation remains a major challenge despite vast efforts reported over many decades and so far still mainly relies on trial and error. Now it is shown that the relative reactivity value (RRV) of thioglycosides is an indicator for revealing stereoselectivities according to four types of acceptors. Mechanistic studies show that the reaction is dominated by two distinct intermediates: glycosyl triflates and glycosyl halides from N‐halosuccinimide (NXS)/TfOH. The formation of glycosyl halide is highly correlated with the production of α‐glycoside. These findings enable glycosylation reactions to be foreseen by using RRVs as an α/β‐selectivity indicator and guidelines and rules to be developed for stereocontrolled glycosylation. 相似文献
998.
999.
Brian Simolon Naseem Aziz Scott Cogan Eric Kurth Simon Lam Susan Petronio James Woolaway Sumith Bandara Sarath Gunapala Jason Mumolo 《Infrared Physics & Technology》2009,52(6):391-394
FLIR Systems, Inc. has designed and fabricated the ISC0501 CMOS readout integrated circuit (ROIC) for quantum well infrared photodetectors (QWIPs). The ISC0501 is a two-color 1024 × 1024 format array with a 30 μm pixel pitch. The ROIC contains a separate analog signal path for each wavelength band. Separate signal paths allow the two-colors to have optimized detector biases, integration times, offsets and gains. This architecture also allows both colors to simultaneously sample a scene and readout the pixel data. This paper will describe the interface, design and features of the ROIC as well as a summary of the characterization test results. A sample image is included from a focal plane array (FPA) built by the Jet Propulsion Laboratory (JPL) using the ISC0501 ROIC with QWIP detectors designed by JPL. 相似文献
1000.
Xin Jiang Feng Po Lam Wu Hoi Lam Tam Dr. King Fai Li Dr. Man Shing Wong Prof. Kok Wai Cheah Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11681-11691
A novel series of diphenylamino‐ and 1,2,4‐triazole‐end‐capped, fluorene‐based, π‐conjugated oligomers that includes extended oligofluorenes and oligothienylfluorenes has been synthesized by means of the palladium‐catalyzed Suzuki cross‐coupling of 9,9‐dibutyl‐7‐(diphenylamino)‐2‐fluorenylboronic acid and the corresponding 1,2,4,‐triazole‐based aryl halide as a key step. It was demonstrated that efficient two‐ and three‐photon excited photoluminescence and lasing in the blue region are obtained by pumping near‐infrared femtosecond lasers on these materials. Although the absorption and emission maxima of the highly fluorescent and extended oligofluorenes reach a saturation limit, there exists an effective conjugation length for an optimum three‐photon absorption cross section in the homologous oligofluorene series. On the other hand, the multiphoton excited emission spectrum and lasing wavelength can easily be modified or tuned by an incorporation of thienyl unit(s) into the fluorene‐based π‐conjugated core with which exceptionally large three‐photon absorption cross sections up to 3.59×10?77 cm6 s2 in the femtosecond regime have been obtained, thereby highlighting the potential of this series of photonic materials. The optimized full width at half‐maximum of the cavityless three‐photon upconverted blue lasing spectra are sharply narrowed to approximately 6 nm with an efficiency of up to 0.013 %. 相似文献