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Cycloaddition of P−C Single Bonds: Stereoselective Formation of Benzo‐1,3,6,2‐trioxaphosphepine Complexes via a Ditopic van der Waals Complex 下载免费PDF全文
Dr. Payal Malik Prof. Dr. Arturo Espinosa Ferao Dr. Gregor Schnakenburg Prof. Dr. Rainer Streubel 《Angewandte Chemie (International ed. in English)》2016,55(41):12693-12697
While phosphaalkenes and phosphanes are known to participate in [4+n] cycloaddition reactions, P?C single bonds are inert in this respect. Herein, reactions of oxaphosphirane complexes with tetrachloro‐ortho‐benzoquinone are presented that reveal a stereoselective reaction of the endocyclic P?C bond to afford benzo‐1,3,6,2‐trioxaphosphepine complexes. High‐level DFT calculations provide evidence that the final product is derived from a sequence of three consecutive steps involving a ditopic van der Waals complex. 相似文献
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Mahesh S. Majik Perunninakulath S. Parameswaran Santosh G. Tilve 《Helvetica chimica acta》2008,91(8):1500-1504
A straightforward synthesis of (S)‐pyrrolam A is described. The synthesis involves in situ generation of the phosphorane 3 , followed by an intramolecular Wittig reaction to furnish (S)‐pyrrolam A. 相似文献
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Five new coumarin derivatives ( 5a , 5b , 5c , 5d , 5e ) with extending para‐bromophenyl at the 3‐position and substituted vinyl at the 7‐position were synthesized and characterized by FT‐IR, 1H NMR, and element analysis. The absorption and fluorescence characteristics of compounds 5a , 5b , 5c , 5d , 5e showed significant dependences on its molecular structure, which possessed large Stokes shifts (up to 8309 cm?1) and high fluorescence quantum yield (up to 0.80) in CH2Cl2. These advantageous spectral properties should allow use in many areas. 相似文献
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Azocinoindole Synthesis by a Gold(I)‐Catalyzed Ring Expansion of 2‐Propargyl‐β‐Tetrahydrocarboline 下载免费PDF全文
Lei Zhang Lina Chang Prof. Hongwen Hu Huaqin Wang Prof. Dr. Zhu‐Jun Yao Prof. Dr. Shaozhong Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(10):2925-2932
A new methodology taking advantage of gold(I)‐catalyzed ring expansion has been developed to assemble tricyclic 1H‐azocino[5,4‐b]indoles from 2‐propargyl‐β‐tetrahydrocarbolines. The azocinoindoles were obtained in moderate to excellent yields; the structure of which was established by X‐ray crystallographic analysis. A mechanism involving regioselective intramolecular hydroarylation, [1,2]‐alkenyl migration and carbon–carbon bond‐fragmentation was proposed. 相似文献
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Chien-Hong Cheng 《中国化学会会志》1988,35(4):261-266
Complexes (η4-PhCH=CHCR=NPh)Fe(CO)3, where R=H(1a) and CH3 were synthesized in excellent yield from the reaction of the corresponding α,β-unsaturated ketimines with excess Fe2(CO)9. Reaction of la with (Ph)2CHLi and (CH3)2(NC)CLi at ?78°C or ambient temperature followed by acid quenching gave trans-PhCH=CHCHRNHPh, where R=CHPH2 and C(CH3)2CN, respectively, in good yield. In the presence of 1 atm. of CO the reaction of 1a with (CH3)2(NC)CLi, followed by CuCl2 oxidation resulted in the formation of a carbamyl choride, trans-PhCH=CHCH[C(CH3)2CN]N(Ph)COCl. This species was converted to a carbamate compound trans-PhCH=CHCH[C(CH3)2 - CN]N(Ph)COOCH3 in MeOH in the presence of Ag+. 相似文献
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Gold‐Catalyzed Oxidative Ring Expansion of 2‐Alkynyl‐1,2‐Dihydropyridines or ‐quinolines: Highly Efficient Synthesis of Functionalized Azepine or Benzazepine Scaffolds 下载免费PDF全文
Ming Chen Dr. Yifeng Chen Ning Sun Jidong Zhao Prof. Yuanhong Liu Prof. Yuxue Li 《Angewandte Chemie (International ed. in English)》2015,54(4):1200-1204
A gold‐catalyzed highly regio‐ and chemoselective oxidative ring expansion of 2‐alkynyl‐1,2‐dihydropyridines and its analogues using pyridine‐N‐oxide as the oxidant has been developed. Ring expansion proceeds through exclusive 1,2‐migration of a vinyl or phenyl group, whereas no 1,2‐H and 1,2‐N migration take place. The reaction provides an efficient and attractive route to various types of medium‐sized azepine derivatives in generally high to excellent yields with a broad functional group tolerance. DFT studies indicate that the reaction proceeds through the formation of a cyclopropyl gold intermediate, and no gold carbene species is involved. 相似文献
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Hannelore Goossens Nicola Piens Dr. Saron Catak Prof. Dr. Michel Waroquier Prof. Dr. Karl W. Törnroos Prof. Dr. Veronique Van Speybroeck Prof. Dr. Matthias D'hooghe Prof. Dr. Norbert De Kimpe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(10):3383-3396
The reactivity of 3‐hydroxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams with regard to the oxidant sodium periodate was evaluated, unexpectedly resulting in the exclusive formation of new 2‐hydroxy‐1,4‐oxazin‐3‐ones through a C3? C4 bond cleavage of the intermediate 4‐formyl‐3‐hydroxy‐β‐lactams followed by a ring expansion. This peculiar transformation stands in sharp contrast with the known NaIO4‐mediated oxidation of 3‐alkoxy‐ and 3‐phenoxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams, which exclusively leads to the corresponding 4‐formyl‐β‐lactams without a subsequent ring enlargement. In addition, this new class of functionalized oxazin‐3‐ones was further evaluated for its potential use as building blocks in the synthesis of a variety of differently substituted oxazin‐3‐ones, morpholin‐3‐ones and pyrazinones. Furthermore, additional insights into the mechanism and the factors governing this new ring‐expansion reaction were provided by means of density functional theory calculations. 相似文献
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A short, efficient synthesis of 2‐methoxy‐6‐alkyl‐1,4‐benzoquinones is described. Ultrasound‐assisted Wittig reaction of alkyltriphenyl phosphonium bromides with o‐vanillin in basic aqueous conditions followed by reduction with Na/n‐BuOH gave 2‐methoxy‐6‐alkylphenols. Oxidation of 2‐methoxy‐6‐alkylphenols with Fremy's salt produced the title compounds. 相似文献
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One‐Pot Synthesis of 3‐Acetyl‐2‐aryl‐3,4‐dihydroquinazolines from N‐[2‐(Azidomethyl)phenyl]benzamides Utilizing Intramolecular Aza‐Wittig Reaction 下载免费PDF全文
Kazuhiro Kobayashi Naoki Matsumoto Mika Nagashima Hiroki Inouchi 《Helvetica chimica acta》2015,98(2):184-189
A new and convenient method for the preparation of 3,4‐dihydroquinazolines 5 with aryl and Ac groups at C(2) and N(3), respectively, has been developed. The key sequence is the formation of aza‐phosphorane intermediates by the reaction of N‐[2‐(azidomethyl)phenyl]benzamides 1 with Ph3P, followed by intramolecular aza‐Wittig reaction and 3‐acetylation, which can be conducted in one‐pot. 相似文献
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Unusual 1,2‐migration reactions of N‐heterocyclic carbene (NHC) on transition metals were investigated using density functional theory calculations. Our results reveal that the electronic properties, ring strain of the four‐membered ring, and aromaticity of NHC play crucial roles in the thermodynamics of such a 1,2‐migration. Further studies show that changing the methylene on the metal center in the reactant with a more electronegative group (NH or O) will lead to the formation of products with nitrogen coordinating to the metal center, whereas other groups (BH, CF2, and SiH2) will make such a 1,2‐migration reverse. In addition, the reversed rearrangement of 1,2‐boron, silyl migration could be thermodynamically and kinetically favorable. 相似文献
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Sinceitsdiscovery ,Wittigreactionhasbecomeoneofprimarymethodsfortheformationofcarbon carbondoublebondsandbeenwidelyusedinthesynthesisofnaturalproducts .1,2 Recently ,itwasfoundthatprimaryalcoholscanundergothetandemreactionofoxidation Wittigreactionwithphos… 相似文献
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Theoretical Investigation of the Reaction Mechanism of the Photoisomerization of 1,2‐Dihydro‐1,2‐azaborine 下载免费PDF全文
The photoisomerization of 1,2‐dihydro‐1,2‐azaborine was investigated by high‐level multireference ab initio and density functional theory calculations. The intermediates (IMs) and transition states (TSs) on the S0 and S1 states were optimized using the state‐averaged complete active space self‐consistent field method. The multireference configuration interaction method with the Davidson correction was used to obtain accurate energetics. Moreover, the conical intersections (CIs), which play a crucial role in photoisomerization, were also optimized. On the basis of the calculation results, the most favorable proposed reaction pathway is as follows: reactant→Franck‐Condon region→TS1→CI→IM0→TS0P→product. The product was not directly formed through the CI, and the IM0 existed on the S0 state. These results show that the isomerization of 1,2‐dihydro‐1,2‐azaborine involves both photoreactions and thermal reactions. The calculated results clarify recent experimental observations. 相似文献
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Ali Ramazani Morteza Rouhani Aram Rezaei Nahid Shajari Ali Souldozi 《Helvetica chimica acta》2011,94(2):282-288
Reactions of biacetyl (=butane‐2,3‐dione) with (N‐isocyanimino)triphenylphosphorane in the presence of aromatic carboxylic acids proceed smoothly at room temperature and under neutral conditions to afford 3‐(5‐aryl‐1,3,4‐oxadiazol‐2‐yl)‐3‐hydroxybutan‐2‐one derivatives in high yields. 相似文献
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Synthesis of a novel β,β′‐tetraalkylporphyrin dimer linked by vinylene was discribed, in which the dimer was readily prepared from a porphyrin‐derived Wittig reagent and a mono‐formylated porphyrin via Wittig reaction. No π‐conjugation between the two porphyrin rings was obserbed, and the dimer was in trans form. 相似文献
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Holger Bera Dr. Holger Braunschweig Prof. Dr. Rainer Dörfler Kai Hammond Andreas Oechsner Krzysztof Radacki Dr. Katharina Uttinger Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(44):12092-12098
We present the synthesis and characterization of disila‐ and distanna ansa half‐sandwich complexes of Group 6 transition metals. These compounds exhibit high ring strain within the ansa bridge, which is the key factor for the insertion of elemental chalcogens. 相似文献
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