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Dr. Manisha Swain Gusein Sadykhov Ruoxi Wang Prof. Dr. Ohyun Kwon 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(40):17718-17724
The dealkenylative alkenylation of alkene C(sp3)−C(sp2) bonds has been an unexplored area for C−C bond formation. Herein 64 examples of β-alkylated styrene derivatives, synthesized through the reactions of readily accessible feedstock olefins with β-nitrostyrenes by ozone/FeII-mediated radical substitutions, are reported. These reactions proceed with good efficiencies and high stereoselectivities under mild reaction conditions and tolerate an array of functional groups. Also demonstrated is the applicability of the strategy through several synthetic transformations of the products, as well as the syntheses of the natural product iso-moracin and the drug (E)-metanicotine. 相似文献
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Andrew J. Smaligo Jason Wu Nikolas R. Burton Allison S. Hacker Aslam C. Shaikh Jason C. Quintana Ruoxi Wang Changmin Xie Ohyun Kwon 《Angewandte Chemie (International ed. in English)》2020,59(3):1211-1215
Reported herein is a one‐pot protocol for the oxodealkenylative introduction of carbonyl functionalities into terpenes and terpene‐derived compounds. This transformation proceeds by Criegee ozonolysis of an alkene, reductive cleavage of the resulting α‐alkoxy hydroperoxide, trapping of the generated alkyl radical with 2,2,6,6‐tetramethylpiperidin‐1‐yl (TEMPO), and subsequent oxidative fragmentation with MMPP. Using readily available starting materials from chiral pool, a variety of carbonyl‐containing products have been accessed rapidly in good yields. 相似文献
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Transition from π Radicals to σ Radicals: Substituent‐Tuned Cyclization of Hydrazonyl Radicals 下载免费PDF全文
Xiu‐Long Yang Prof. Dr. Wei Yu Prof. Dr. Bing Han 《Angewandte Chemie (International ed. in English)》2014,53(12):3158-3162
Hydrazonyl radicals are known for their π‐electronic structures; however, their σ‐electronic structures have not been reported as yet. Herein, we show that readily accessible β,γ‐ and γ,δ‐unsaturated N‐trichloroacetyl and N‐trifluoroacetyl hydrazones can be conveniently converted into hydrazonyl σ radicals, which subsequently undergo 5‐exo‐trig radical cyclization at the N1 or N2 atom to form pyrazolines and azomethine imines, respectively. 相似文献
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Ute Wild Stefanie Federle Dr. Arne Wagner Dr. Elisabeth Kaifer Prof. Dr. Hans‐Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(34):11971-11976
We present a new option for metal‐free σ‐bond activation, making use of oxidized, guanidino‐functionalized aromatic compounds (GFAs). We demonstrate this new option by the homocoupling reactions of thiols and phosphines. The kinetics and the reaction pathway were studied by a number of experiments (including heterocoupling of thiols and phosphines), supported by quantum‐chemical computations. Reaction of the oxidized GFA with p‐dihydrobenzoquinone to give p‐benzoquinone shows that typical proton‐coupled electron‐transfer reactions are also possible. 相似文献
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David J. Liptrot Prof. Michael S. Hill Dr. Mary F. Mahon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9871-9874
Reactions between PhSiH3 and alkali‐metal diamidoalkylmagnesiates ([M{N(SiMe3)2}2MgBu], M=Li, Na, K) provide either selective alkyl metathesis or the formation of polyhydride aggregates contingent upon the identity of the Group 1 metal. In the case of [M{N(SiMe3)2}2MgBu], this reactivity results in a structurally unprecedented dodecametallic decahydride cluster species. 相似文献
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Redox‐Switchable 20π‐, 19π‐, and 18π‐Electron 5,10,15,20‐Tetraaryl‐5,15‐diazaporphyrinoid Nickel(II) Complexes 下载免费PDF全文
Takaharu Satoh Prof. Dr. Mao Minoura Prof. Dr. Haruyuki Nakano Prof. Dr. Ko Furukawa Prof. Dr. Yoshihiro Matano 《Angewandte Chemie (International ed. in English)》2016,55(6):2235-2238
The first examples of air‐stable 20π‐electron 5,10,15,20‐tetraaryl‐5,15‐diaza‐5,15‐dihydroporphyrins, their 18π‐electron dications, and the 19π‐electron radical cation were prepared through metal‐templated annulation of nickel(II) bis(5‐arylamino‐3‐chloro‐8‐mesityldipyrrin) complexes followed by oxidation. The neutral 20π‐electron derivatives are antiaromatic and the cationic 18π‐electron derivatives are aromatic in terms of the magnetic criterion of aromaticity. The meso N atoms in these diazaporphyrinoids give rise to characteristic redox and optical properties for the compounds that are not typical of isoelectronic 5,10,15,20‐tetraarylporphyrins. 相似文献
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Visible‐Light‐Mediated Addition of α‐Aminoalkyl Radicals to [60]Fullerene by Using Photoredox Catalysts 下载免费PDF全文
Dr. Yoshihiro Miyake Yuya Ashida Dr. Kazunari Nakajima Prof. Dr. Yoshiaki Nishibayashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):6120-6125
The functionalization of fullerene has been extensively studied and various fullerene derivatives have been synthesized. We have succeeded in the functionalization of [60]fullerene by using α‐aminoalkyl radicals generated by visible‐light‐mediated single‐electron oxidation of α‐silylamines as synthetic intermediates. In these reactions, the introduction of diarylamino groups, which are useful electron donors, has been easily achieved. 相似文献
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β‐Amyrin Biosynthesis: The Methyl‐30 Group of (3S)‐2,3‐Oxidosqualene Is More Critical to Its Correct Folding To Generate the Pentacyclic Scaffold than the Methyl‐24 Group 下载免费PDF全文
Prof. Dr. Tsutomu Hoshino Yuri Miyahara Masaki Hanaoka Kazunari Takahashi Ikki Kaneko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15769-15784
Oxidosqualene cyclases catalyze the transformation of oxidosqualene ( 1 ) into numerous cyclic triterpenes. Enzymatic reactions of 24‐noroxidosqualene ( 8 ) and 30‐noroxidosqualene ( 9 ) with Euphorbia tirucalli β‐amyrin synthase were conducted to examine the role of the branched methyl groups of compound 1 in the β‐amyrin biosynthesis. Substrate 8 almost exclusively afforded 30‐nor‐β‐amyrin (>95.5 %), which was produced through a normal cyclization pathway, along with minor products (<4.5 %). However, a lack of the Me‐30 group (analogue 9 ) resulted in significantly high production of premature cyclization products, including 6/6/6/5‐fused tetracyclic and 6/6/6/6/5‐fused pentacyclic skeletons (64.6 %). In addition, the fully cyclized product (35.4 %) having the 6/6/6/6/6‐fused pentacycle was produced; however, the normally cyclized product, 29‐nor‐β‐amyrin was present in only 18.6 % of these products. The conversion yield of substrate 8 possessing a Z‐Me group at the terminus was approximately twofold greater than that of compound 9 with an E‐Me group. Thus, the Me‐30 group is essential for the correct folding of a chair–chair–chair–boat–boat conformation of compound 1 for the production of the β‐amyrin scaffold, whereas the Me‐24 group exerts little influence on the normal polycyclization cascade. Here, we show that the Me‐30 group plays critical roles in constructing the ordered architecture of a chair–chair–chair–boat–boat structure, in facilitating the ring‐expansion reactions, and in performing the final deprotonation reaction at the correct position. 相似文献
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Ryousuke Ito Ippei Hashimoto Yukari Masukawa Prof. Dr. Tsutomu Hoshino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(50):17150-17158
The function of the active‐site residues of oxidosqualene cyclases (OSCs) has been presumed mainly in light of the product distribution; however, not much research has been performed into the enzymatic activity of mutated OSCs. β‐Amyrin, which is widely found in the plant kingdom, is classified as an OSC; mutational studies on β‐amyrin cyclase are very limited. Six site‐specific mutations targeted at the Phe728 residue of Euphorbia tirucalli β‐amyrin synthase (EtAS) were constructed to inspect the function of this aromatic residue. We developed a simple method to evaluate the in vivo enzymatic activity; the expression levels of EtASs and the quantities of the cyclic triterpenes produced were determined by use of western blot and GC analyses, respectively. Measurement of the relative in vivo activity of the mutants versus that of the wild‐type enzyme showed that the Ala, Met, His, and Trp variants had significantly decreased activity, but that the Tyr mutant had a high activity, which was nearly the same as that of the wild‐type enzyme. In contrast to Tyr, Ala and Met possess no π‐electrons; thus, the role of Phe728 is to stabilize the cationic intermediates, resulting in facilitation of the ring‐expansion processes, especially by stabilizing the secondary cations. The decreased activity of the Trp mutant is ascribed to the introduction of a large steric bulk, leading to looser binding of oxidosqualene in the Trp variant. The His mutant afforded germanicol as the main product, indicating that the Phe residue is located near the D/E‐ring‐formation site. Changes in the steric bulk gave some cationic intermediates, resulting in the formation of 13 cyclic triterpenes, including an unnatural triterpene, (17E)‐dammara‐17(20),24‐dien‐3β‐ol, and isoursenol, which has rarely been found in nature. In this study, we provide the first experimental evidence that cation–π interactions play a key role in the catalytic action of OSCs. 相似文献
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Jan L. Wolf Martin A. Suhm Prof. Dr. Thomas Zeuch Dr. 《Angewandte Chemie (International ed. in English)》2009,48(12):2231-2235
The new approach of kinetically controlled ozone removal suppresses particle formation in laboratory ozonolysis experiments for methylcyclohexene and methylenecyclohexane (MCHa) at excess alkene concentrations (see graph). The results support the hypothesis that peroxy radicals are involved in organic nucleation and particle‐growth mechanisms.
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Atsuro Takai Claude P. Gros Dr. Jean‐Michel Barbe Dr. Roger Guilard Prof. Dr. Shunichi Fukuzumi Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(13):3110-3122
π–π assisted : Photoinduced electron transfer from cofacial porphyrin dimers to electron acceptors is prominently accelerated, whereas the back electron transfer is decelerated, relative to the corresponding porphyrin monomer (see figure).
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Lina Ma Wenjuan Li Hui Xi Xiaohui Bai Enlu Ma Dr. Xiaoyu Yan Prof. Dr. Zhiping Li 《Angewandte Chemie (International ed. in English)》2016,55(35):10410-10413
Exploiting catalytic carbonyl–olefin metathesis is an ongoing challenge in organic synthesis. Reported herein is an FeCl3‐catalyzed ring‐closing carbonyl–olefin metathesis. The protocol allows access to a range of carbo‐/heterocyclic alkenes with good efficiency and excellent trans diastereoselectivity. The methodology presents one of the rare examples of catalytic ring‐closing carbonyl–olefin metathesis. This process is proposed to take place by FeCl3‐catalyzed oxetane formation followed by retro‐ring‐opening to deliver metathesis products. 相似文献
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Amidyl Radicals by Oxidation of α‐Amido‐oxy Acids: Transition‐Metal‐Free Amidofluorination of Unactivated Alkenes 下载免费PDF全文
Heng Jiang Prof. Dr. Armido Studer 《Angewandte Chemie (International ed. in English)》2018,57(33):10707-10711
A three‐component transition‐metal‐free amidofluorination of unactivated alkenes and styrenes is presented. α‐Amido‐oxy acids are introduced as efficient and easily accessible amidyl radical precursors that are oxidized by a photoexcited organic sensitizer (Mes‐Acr‐Me) to the corresponding carboxyl radical. Sequential CO2 and aldehyde/ketone fragmentation leads to an N‐centered radical that adds to an alkene. Commercial Selectfluor is used to trap the adduct radical through fluorine‐atom transfer. The transformation features by high functional‐group tolerance, broad substrate scope, and practical mild conditions. Mechanistic studies support the radical nature of the cascade. 相似文献