排序方式: 共有46条查询结果,搜索用时 296 毫秒
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Alison S. H. Ryder Dr. William B. Cunningham George Ballantyne Tom Mules Anna G. Kinsella Jacob Turner-Dore Dr. Catherine M. Alder Lee J. Edwards Dr. Blandine S. J. McKay Dr. Matthew N. Grayson Dr. Alexander J. Cresswell 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):15096-15101
A practical, catalytic entry to α,α,α-trisubstituted (α-tertiary) primary amines by C−H functionalisation has long been recognised as a critical gap in the synthetic toolbox. We report a simple and scalable solution to this problem that does not require any in situ protection of the amino group and proceeds with 100 % atom-economy. Our strategy, which uses an organic photocatalyst in combination with azide ion as a hydrogen atom transfer (HAT) catalyst, provides a direct synthesis of α-tertiary amines, or their corresponding γ-lactams. We anticipate that this methodology will inspire new retrosynthetic disconnections for substituted amine derivatives in organic synthesis, and particularly for challenging α-tertiary primary amines. 相似文献
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AJ Cresswell SG Davies JA Lee MJ Morris PM Roberts JE Thomson 《The Journal of organic chemistry》2012,77(17):7262-7281
A diastereodivergent hydroxyfluorination protocol enabling the direct conversion of some conformationally biased allylic amines to the corresponding diastereoisomeric amino fluorohydrins has been developed. Sequential treatment of a conformationally biased allylic amine with 2 equiv of HBF(4)·OEt(2) followed by m-CPBA promotes epoxidation of the olefin on the face proximal to the amino group under hydrogen-bonded direction from the in situ formed ammonium ion. Regioselective and stereospecific epoxide ring-opening by transfer of fluoride from a BF(4)(-) ion (an S(N)2-type process at the carbon atom distal to the ammonium moiety) then occurs in situ to give the corresponding amino fluorohydrin. Alternatively, an analogous reaction using 20 equiv of HBF(4)·OEt(2) results in preferential epoxidation of the opposite face of the olefin, which is followed by regioselective and stereospecific epoxide ring-opening by transfer of fluoride from a BF(4)(-) ion (an S(N)2-type process at the carbon atom distal to the ammonium moiety). The synthetic utility of this methodology is demonstrated via its application to a synthesis of 4-deoxy-4-fluoro-l-xylo-phytosphingosine and 4-deoxy-4-fluoro-l-lyxo-phytosphingosine, each in five steps from Garner's aldehyde. 相似文献
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The fluorescence of rhenium(IV) and thulium(III) ions doped singly and together in the most host lattice Cs2NaYCl6 is studied. Energy transfer between Re4+ and Tm3+ ions is demonstrated and is shown to provide two-step up-conversion to the 1D2 and 1G4 levels of the Tm3+ ion, both of which emit in the blue. 相似文献
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In this paper we develop numerical algorithms for the continuationof degenerate homoclinic connections in planar systems. We considerthe case where the equilibrium point has zero trace and twocases of higher-order degeneracies. The method we propose isable to continue homoclinic connections of order up to codimension-four.Application of the algorithm to four examples supports its validityand demonstrates its usefulness. 相似文献
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AM Cardoso SM Alexandre CM Barros AJ Correia NM Nibbering 《Rapid communications in mass spectrometry : RCM》1999,13(19):1885-1888
The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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DJ Smith KW Ledingham RP Singhal T McCanny P Graham HS Kilic P Tzallas C Kosmidis AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1366-1373
With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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X Fang KW Ledingham P Graham DJ Smith T McCanny RP Singhal AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1390-1397
The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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Room‐Temperature Gold‐Catalysed Arylation of Heteroarenes: Complementarity to Palladium Catalysis
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Dr. Alexander J. Cresswell Prof. Dr. Guy C. Lloyd‐Jones 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(36):12641-12645
Tailoring of the pre‐catalyst, the oxidant and the arylsilane enables the first room‐temperature, gold‐catalysed, innate C?H arylation of heteroarenes. Regioselectivity is consistently high and, in some cases, distinct from that reported with palladium catalysis. Tolerance to halides and boronic esters, in both the heteroarene and silane partners, provides orthogonality to Suzuki–Miyaura coupling. 相似文献
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Dr. Alexander J. Cresswell Dr. Stanley T.‐C. Eey Prof. Dr. Scott E. Denmark 《Angewandte Chemie (International ed. in English)》2015,54(52):15642-15682
Although recent years have witnessed significant advances in the development of catalytic, enantioselective halofunctionalizations of alkenes, the related dihalogenation of olefins to afford enantioenriched vicinal dihalide products remains comparatively underdeveloped. However, the growing number of complex natural products bearing halogen atoms at stereogenic centers has underscored this critical gap in the synthetic chemist’s arsenal. This Review highlights the selectivity challenges inherent in the design of enantioselective dihalogenation processes, and formulates a mechanism‐based classification of alkene dihalogenations, including those that may circumvent the “classical” haliranium (or alkene‐dihalogen π‐complex) intermediates. A variety of metal and main group halide reagents that have been used for the dichlorination or dibromination of alkenes are discussed, and the proposed mechanisms of these transformations are critically evaluated. 相似文献