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SYNTHESIS OF 5,7-DIHYDRODIBENZOMETALLEPINS VIA A NEW DI-GRIGNARD OR DILITHIUM REAGENT
Thermally robust metallacycles (L=2-, M=Ti, Zr, Hf) and have been obtained from the newly developed reagents, L2 and L2, as has the silylated derivative, 2.A new radical anion of 9,10-dihydrophenanthrene derived from the reaction of lithium and LCl2 or LBr2 in thf has been detected.
Leung, Wing-Por,Raston, Colin L.
p. C1 - C4
(1982)
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ELECTRO-ORGANIC REACTIONS. PART 29: CATHODIC REDUCTION ACTIVATED BY ARENE-CHROMIUM TRICARBONYL COMLEXATION
Chromium tricarbonyl-arene complexes are easily reduced electrochemically and reduction potentials ca. 0.6 V less than the corresponding arenes; hence stilbene is activated towards hydrodimerisation and phenanthrene towards hydrogenation
Chiu, Y. Lin,Sant'ana, Antonio E. G.,Utley, James H. P.
p. 1349 - 1352
(1987)
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Aromatic compound hydrogenation and hydrodeoxygenation method and application thereof
The invention belongs to the technical field of medicines, and discloses an aromatic compound hydrogenation and hydrodeoxygenation method under mild conditions and application of the method in hydrogenation and hydrodeoxygenation reactions of the aromatic compounds and related mixtures. Specifically, the method comprises the following steps: contacting the aromatic compound or a mixture containing the aromatic compound with a catalyst and hydrogen with proper pressure in a solvent under a proper temperature condition, and reacting the hydrogen, the solvent and the aromatic compound under the action of the catalyst to obtain a corresponding hydrogenation product or/and a hydrodeoxygenation product without an oxygen-containing substituent group. The invention also discloses specific implementation conditions of the method and an aromatic compound structure type applicable to the method. The hydrogenation and hydrodeoxygenation reaction method used in the invention has the advantages of mild reaction conditions, high hydrodeoxygenation efficiency, wide substrate applicability, convenient post-treatment, and good laboratory and industrial application prospects.
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Paragraph 0094-0095; 0106-0113

(2021/05/29)

A facile and versatile electro-reductive system for hydrodefunctionalization under ambient conditions
A general electrochemical system for reductive hydrodefunctionalization is described, employing the inexpensive and easily available triethylamine (Et3N) as a sacrificial reductant. This protocol is characterized by facile operation, sustainable conditions, and exceptionally wide substrate scope covering the cleavage of C-halogen, N-S, N-C, O-S, O-C, C-C and C-N bonds. Notably, the selectivity and capability of reduction can be conveniently switched by simple incorporation or removal of an alcohol as a co-solvent.
Huang, Binbin,Guo, Lin,Xia, Wujiong
supporting information
p. 2095 - 2103
(2021/03/26)

On the multifaceted roles of NiSx in hydrodearomatization reactions catalyzed by unsupported Ni-promoted MoS2
A series of unsupported Ni-Mo sulfide catalysts with varying Ni contents (0.13–0.72 molNi molNi+Mo-1) was post-synthetically treated with concentrated HCl to remove large crystallites of accessible NiSx. These sulfide particles inevitably form and grow at Ni concentrations required for the synthesis, but generally have very low activities. In all cases, Ni concentrations were greatly reduced by the HCl treatment. While this ‘leaching’ strategy successfully improved the reaction rates of high Ni-content (>0.4 molNi molmetal-1) catalysts for the hydrogenation of phenanthrene, modest to drastic decreases in catalytic rates (×0.1–0.8) were registered for catalysts with lower Ni concentrations. For the lowest Ni-loaded catalyst (0.05 molNi molmetal-1), HCl treatment caused a dramatic loss of specific surface area and catalytic activity by more than a factor of 6 and shifted the selectivity pattern to that of pure MoS2. These observations allow us to conclude that Ni atoms incorporated at the slab edges are inherently susceptible to HCl attack. NiSx, however, are the preferential sites at which HCl induces dissolution. Experiments with inter-particle mixtures and segregated beds of NiSx and MoS2 demonstrate that NiSx not only activates H2, but also acts as a reservoir to dynamically incorporate Ni in the MoS2 slabs at reaction conditions. These beneficial effects are reduced, as nickel sulfide particles become excessively abundant as typical for high Ni-content catalysts, for which edge substitution by Ni is near or at its maximum. The areal activity and concentration of chemisorbed nitric oxide (NO) are well correlated for the leached catalysts, with the exception of the lowest Ni-containing catalyst that has a low degree of Ni edge substitution (20% of total edge atoms) and predominantly unpromoted sites. This linear correlation shows that the Ni-promoted sites are more than five-fold as active as the unpromoted sites.
Ji, Yinjie,Lercher, Johannes A.,Shi, Hui,Vogelgsang, Ferdinand
p. 212 - 223
(2020/09/16)

Highly Active Superbulky Alkaline Earth Metal Amide Catalysts for Hydrogenation of Challenging Alkenes and Aromatic Rings
Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP)2]2 (1-Ae) and Ae[N(TRIP)(DIPP)]2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr3, DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene.
Eyselein, Jonathan,F?rber, Christian,Grams, Samuel,Harder, Sjoerd,Knüpfer, Christian,Langer, Jens,Martin, Johannes,Thum, Katharina,Wiesinger, Michael
supporting information
p. 9102 - 9112
(2020/03/30)

Birch-Type Photoreduction of Arenes and Heteroarenes by Sensitized Electron Transfer
The direct reduction of arenes and heteroarenes by visible-light irradiation remains challenging, as the energy of a single photon is not sufficient for breaking aromatic stabilization. Shown herein is that the energy accumulation of two visible-light photons allows the dearomatization of arenes and heteroarenes. Mechanistic investigations confirm that the combination of energy-transfer and electron-transfer processes generates an arene radical anion, which is subsequently trapped by hydrogen-atom transfer and finally protonated to form the dearomatized product. The photoreduction converts planar aromatic feedstock compounds into molecular skeletons that are of use in organic synthesis.
Chatterjee, Anamitra,K?nig, Burkhard
supporting information
p. 14289 - 14294
(2019/08/30)

Experimental and Theoretical Studies on the Aqueous Solvation and Reactivity of SmCl2 and Comparison with SmBr2 and SmI2
Water addition to Sm(II) has been shown to increase reactivity for both SmI2 and SmBr2. Previous work in our groups has demonstrated that this increase in reactivity can be attributed to coordination induced bond weakening enabling substrate reduction through proton-coupled electron transfer. The present work examines the interaction of water with samarium dichloride (SmCl2) and illustrates the importance of the Sm-X interaction and bond distance upon water addition critical for the reactivity of the reagent system. Born-Oppenheimer molecular dynamics simulations identify substantial variations among the reductants created in solution upon water addition to SmI2, SmBr2, and SmCl2 with the latter showing the least halide dissociation. This results in a lower water coordination number for SmCl2, creating a more powerful reducing system. As previously shown with the other SmX2-water systems, coordination-induced bond-weakening of the O-H bond of water bound to Sm(II) results in significant bond weakening. In the case of SmCl2, the bond weakening is estimated to be in the range of 83 to 88.5 kcal/mol.
Ramírez-Solís, Alejandro,Bartulovich, Caroline O.,León-Pimentel, César Iván,Saint-Martin, Humberto,Anderson, William R.,Flowers, Robert A.
supporting information
p. 13927 - 13932
(2019/10/16)

Aerobic and Ligand-Free Manganese-Catalyzed Homocoupling of Arenes or Aryl Halides via in Situ Formation of Aryllithiums
Ligand-free manganese-catalyzed homocoupling of arenes or aryl halides can be carried out under aerobic conditions via the in situ formation of the corresponding aryllithiums. A wide range of biaryls and derivatives has been obtained, and a mechanism involving monomeric manganese-oxo complexes has been proposed on the basis of DFT calculations.
Liu, Yujia,Bergès, Julien,Zaid, Yassir,Chahdi, Fouad Ouazzani,Van Der Lee, Arie,Harakat, Dominique,Clot, Eric,Jaroschik, Florian,Taillefer, Marc
p. 4413 - 4420
(2019/03/26)

Hydrodehalogenation of Aryl Halides through Direct Electrolysis
A catalyst- and metal-free electrochemical hydrodehalogenation of aryl halides is disclosed. Our reaction by a flexible protocol is operated in an undivided cell equipped with an inexpensive graphite rod anode and cathode. Trialkylamines nBu3N/Et3N behave as effective reductants and hydrogen atom donors for this electrochemical reductive reaction. Various aryl and heteroaryl bromides worked effectively. The typically less reactive aryl chlorides and fluorides can also be smoothly converted. The utility of our method is demonstrated by detoxification of harmful pesticides and hydrodebromination of a dibrominated biphenyl (analogues of flame-retardants) in gram scale.
Ke, Jie,Wang, Hongling,Zhou, Liejin,Mou, Chengli,Zhang, Jingjie,Pan, Lutai,Chi, Yonggui Robin
supporting information
p. 6911 - 6914
(2019/05/10)

Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca2N]+?e- in an Alcoholic Solvent: An Analogue of Solvated Electrons
Birch reduction of aromatic systems by solvated electrons in alkali metal-ammonia solutions is widely recognized as a key reaction that functionalizes highly stable π-conjugated organic systems. In spite of recent advances in Birch reduction with regard to reducing agent and reaction conditions, there remains an ongoing challenge to develop a simple and efficient Birch reaction under mild conditions. Here, we demonstrate that the inorganic electride [Ca2N]+?e- promotes the Birch reduction of polycyclic aromatic hydrocarbons (PAHs) and naphthalene under alcoholic solvent in the vicinity of room temperature as a solid-type analogy to solvated electrons in alkali metal ammonia solutions. The anionic electrons from electride [Ca2N]+?e- are transferred to PAHs and naphthalene via alcoholysis in a polar cosolvent medium. It is noteworthy that a high conversion yield to the hydrogenated products is ascribed to the extremely high electron transfer efficiency of 98%. This simple protocol utilizing an inorganic electride offers a direct and practical strategy for the reduction of aromatic compounds and provides an outstanding reducing agent for synthetic chemistry.
Yoo, Byung Il,Kim, Ye Ji,You, Youngmin,Yang, Jung Woon,Kim, Sung Wng
supporting information
p. 13847 - 13853
(2018/11/23)

Strontium-mediated selective protonation of unsaturated linkage of aromatic hydrocarbons and these derivatives
The selective protonation of aromatic hydrocarbons with at least two or more aromatic rings and aromatic compounds bearing unsaturated linkages can be achieved by metallic strontium metal with ammonium chloride and iodine, or ammonium iodide in tetrahydrofuran. The reaction system is ammonia-free in room temperature and the reaction proceeds high selectivity in moderate to good yields.
Ohmura, Satoshi D.,Ueno, Masaharu,Miyoshi, Norikazu
supporting information
p. 2268 - 2271
(2018/05/16)

Novel electronic salt system and method for reducing unsaturated hydrocarbon compound
The invention discloses an electronic salt system and a method for reducing unsaturated hydrocarbon compounds by using the electronic salt system, belongs to the field of organic synthesis, and solvesthe problems such as complicated operation, harsh conditions, easy generation of complex over-reduction products of methods for reducing the unsaturated hydrocarbon compounds in the prior art. An electron salt may be synthesized by an alkali metal reagent, an ether and an alcohol, the ether can be a crown ether or a cryptand; and the method adopts the electronic salt system, the unsaturated hydrocarbon compounds is reduced by the electronic salt system in an organic solvent. The method for reducing the unsaturated hydrocarbon compounds is used for reducing the unsaturated hydrocarbon compounds.
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Paragraph 0109-0113

(2018/09/08)

Active Sites on Nickel-Promoted Transition-Metal Sulfides That Catalyze Hydrogenation of Aromatic Compounds
Hydrogenation on Mo and W sulfides occurs at the edges of the sulfide slabs. The rate of hydrogen addition is directly proportional to the concentration of sulfhydryl (SH) groups at the slab edge and the metal atom attached to it. Sulfhydryl groups vicinal to edge-incorporated Ni hydrogenate with much higher rates than SH close to Mo and W. Each subset of SH groups, however, exhibits nearly identical intrinsic activity and selectivity, independent of the sulfide composition. The higher activity of Ni-WS2 compared to Ni-MoS2 stems from a higher concentration of SH groups on the former sulfide associated with a higher tendency of its surface vacancies to react with H2.
Luo, Wanqiu,Shi, Hui,Schachtl, Eva,Gutiérrez, Oliver Y.,Lercher, Johannes A.
supporting information
p. 14555 - 14559
(2018/09/25)

Experimental and Theoretical Studies on the Implications of Halide-Dependent Aqueous Solvation of Sm(II)
The addition of water to samarium(II) has been demonstrated to have a significant impact on the reduction of organic substrates, with the majority of research dedicated to the most widely used reagent, samarium diiodide (SmI2). The work presented herein focuses on the reducing capabilities of samarium dibromide (SmBr2) and demonstrates how the modest change in halide ligand results in observable mechanistic differences between the SmBr2-water and the SmI2-water systems that have considerable implications in terms of reactivity between the two reagents. Quantum chemical results from Born-Oppenheimer molecular dynamics simulations show significant differences between SmI2-water and SmBr2-water, with the latter displaying less dissociation of the halide, which results in a lower coordination number for water. Experimental results are consistent with computational results and demonstrate that the coordination sphere of SmBr2 is saturated at lower concentrations of water. In addition, coordination-induced bond-weakening of the O-H bond is demonstrably different for water bound to SmBr2, leading to an estimated O-H bond-weakening of at least 83 kcal/mol, nearly 10 kcal/mol larger than the bond-weakening observed in SmI2-H2O. Experimental results also demonstrate that the use of alcohols in place of water with SmBr2 leads to substrate reduction, albeit several orders of magnitude slower than for SmBr2-water. The difference in rates resulting from the change in proton donor is attributed to a rate-limiting proton-coupled electron transfer in SmBr2-water and a sequential electron transfer then proton transfer in SmBr2-alcohol systems, where electron transfer is rate-limiting.
Ramírez-Solís, Alejandro,Bartulovich, Caroline O.,Chciuk, Tesia V.,Hernández-Cobos, Jorge,Saint-Martin, Humberto,Maron, Laurent,Anderson, William R.,Li, Anna M.,Flowers, Robert A.
supporting information
p. 16731 - 16739
(2018/12/11)

Dimerization of the Benzyl Radical in a High-Temperature Pyrolysis Reactor Investigated by IR/UV Ion Dip Spectroscopy
We investigate the self-reaction of benzyl, C7H7, in a high-temperature pyrolysis reactor. The work is motivated by the observation that resonance-stabilized benzyl radicals can accumulate in reactive environments and contribute to the formation of polycyclic aromatic hydrocarbons (PAHs) and soot. Reaction products are detected by IR/UV ion dip spectroscopy, using infrared radiation from the free electron laser FELIX, and are identified by comparison with computed spectra. Among the reaction products identified by their IR absorption are several PAHs linked to toluene combustion such as bibenzyl, phenanthrene, diphenylmethane, and fluorene. The identification of 9,10-dihydrophenanthrene provides evidence for a mechanism of phenanthrene formation from bibenzyl that proceeds by initial cyclization rather than an initial hydrogen loss to stilbene.
Hirsch, Florian,Constantinidis, Philipp,Fischer, Ingo,Bakels, Sjors,Rijs, Anouk M.
p. 7647 - 7652
(2018/05/03)

Secondary amides as hydrogen atom transfer promoters for reactions of samarium diiodide
Two secondary amides (N-methylacetamide and 2-pyrrolidinone) were used as additives with SmI2 in THF to estimate the extent of N-H bond weakening upon coordination. Mechanistic and synthetic studies demonstrate significant bond-weakening, providing a reagent system capable of reducing a range of substrates through formal hydrogen atom transfer.
Chciuk, Tesia V.,Li, Anna M.,Vazquez-Lopez, Andres,Anderson, William R.,Flowers, Robert A.
supporting information
p. 290 - 293
(2017/11/27)

Electron-Transfer and Hydride-Transfer Pathways in the Stoltz–Grubbs Reducing System (KOtBu/Et3SiH)
Recent studies by Stoltz, Grubbs et al. have shown that triethylsilane and potassium tert-butoxide react to form a highly attractive and versatile system that shows (reversible) silylation of arenes and heteroarenes as well as reductive cleavage of C?O bonds in aryl ethers and C?S bonds in aryl thioethers. Their extensive mechanistic studies indicate a complex network of reactions with a number of possible intermediates and mechanisms, but their reactions likely feature silyl radicals undergoing addition reactions and SH2 reactions. This paper focuses on the same system, but through computational and experimental studies, reports complementary facets of its chemistry based on a) single-electron transfer (SET), and b) hydride delivery reactions to arenes.
Smith, Andrew J.,Young, Allan,Rohrbach, Simon,O'Connor, Erin F.,Allison, Mark,Wang, Hong-Shuang,Poole, Darren L.,Tuttle, Tell,Murphy, John A.
supporting information
p. 13747 - 13751
(2017/10/12)

Nickel-mediated decarbonylation of simple unstrained ketones through the cleavage of carbon-carbon bonds
Despite advances in methods for the decarbonylation of aldehydes, the decarbonylation of ketones has been met with limited success because this process requires the activation of two inert carbon-carbon bonds. All of the decarbonylation reactions of simple unstrained ketones reported to date require the addition of a stoichiometric rhodium complex. We report herein the nickel/N-heterocyclic carbene-mediated decarbonylation of simple diaryl ketones. This reaction shows unique acceleration effects based on the presence of both electron-donating and electron-withdrawing groups.
Morioka, Toshifumi,Nishizawa, Akihiro,Furukawa, Takayuki,Tobisu, Mamoru,Chatani, Naoto
supporting information
p. 1416 - 1419
(2017/02/10)

Acid-Catalyzed Skeletal Rearrangements in Arenes: Aryl versus Alkyl Ring Pirouettes in Anthracene and Phenanthrene
In 1 M triflic acid/dichloroethane, anthracene is protonated at C9, and the resulting 9-anthracenium ion is easily observed by NMR at ambient temperature. When heated as a dilute solution in triflic acid/dichloroethane, anthracene undergoes conversion to phenanthrene as the major volatile product. Minor dihydro and tetrahydro products are also observed. MALDI analysis supports the simultaneous formation of oligomers, which represent 10-60% of the product. Phenanthrene is nearly inert to the same superacid conditions. DFT and CCSD(T)//DFT computational models were constructed for isomerization and automerization mechanisms. These reactions are believed to occur by cationic ring pirouettes which pass through spirocyclic intermediates. The direct aryl pirouette mechanism for anthracene has a predicted DFT barrier of 33.6 kcal/mol; this is too high to be consistent with experiment. The ensemble of experimental and computational models supports a multistep isomerization process, which proceeds by reduction to 1,2,3,4-tetrahydroanthracene, acid-catalyzed isomerization to 1,2,3,4-tetrahydrophenanthrene with a predicted DFT barrier of 19.7 kcal/mol, and then reoxidation to phenanthrene. By contrast, DFT computations support a direct pirouette mechanism for automerization of outer ring carbons in phenanthrene, a reaction demonstrated previously by Balaban through isotopic labeling.
Skraba-Joiner, Sarah L.,Brulet, Jeffrey W.,Song, Min K.,Johnson, Richard P.
p. 13076 - 13083
(2017/12/26)

Au-catalyzed biaryl coupling to generate 5- to 9-membered rings: Turnover-limiting reductive elimination versus π-complexation
The intramolecular gold-catalyzed arylation of arenes by aryl-trimethylsilanes has been investigated from both mechanistic and preparative aspects. The reaction generates 5- to 9-membered rings, and of the 44 examples studied, 10 include a heteroatom (N, O). Tethering of the arene to the arylsilane provides not only a tool to probe the impact of the conformational flexibility of Ar-Au-Ar intermediates, via systematic modulation of the length of aryl-aryl linkage, but also the ability to arylate neutral and electron-poor arenes-substrates that do not react at all in the intermolecular process. Rendering the arylation intramolecular also results in phenomenologically simpler reaction kinetics, and overall these features have facilitated a detailed study of linear free energy relationships, kinetic isotope effects, and the first quantitative experimental data on the effects of aryl electron demand and conformational freedom on the rate of reductive elimination from diaryl-gold(III) species. The turnover-limiting step for the formation of a series of fluorene derivatives is sensitive to the reactivity of the arene and changes from reductive elimination to π-complexation for arenes bearing strongly electron-withdrawing substituents (σ > 0.43). Reductive elimination is accelerated by electron-donating substituents (ρ = -2.0) on one or both rings, with the individual σ-values being additive in nature. Longer and more flexible tethers between the two aryl rings result in faster reductive elimination from Ar-Au(X)-Ar and lead to the π-complexation of the arene by Ar-AuX2 becoming the turnover-limiting step.
Corrie, Tom J. A.,Ball, Liam T.,Russell, Christopher A.,Lloyd-Jones, Guy C.
supporting information
p. 245 - 254
(2017/05/29)

Au-Catalyzed Biaryl Coupling to Generate 5- To 9-Membered Rings: Turnover-Limiting Reductive Elimination versus ?-Complexation
The intramolecular gold-catalyzed arylation of arenes by aryl-trimethylsilanes has been investigated from both mechanistic and preparative aspects. The reaction generates 5- to 9-membered rings, and of the 44 examples studied, 10 include a heteroatom (N, O). Tethering of the arene to the arylsilane provides not only a tool to probe the impact of the conformational flexibility of Ar-Au-Ar intermediates, via systematic modulation of the length of aryl-aryl linkage, but also the ability to arylate neutral and electron-poor arenes - substrates that do not react at all in the intermolecular process. Rendering the arylation intramolecular also results in phenomenologically simpler reaction kinetics, and overall these features have facilitated a detailed study of linear free energy relationships, kinetic isotope effects, and the first quantitative experimental data on the effects of aryl electron demand and conformational freedom on the rate of reductive elimination from diaryl-gold(III) species. The turnover-limiting step for the formation of a series of fluorene derivatives is sensitive to the reactivity of the arene and changes from reductive elimination to ?-complexation for arenes bearing strongly electron-withdrawing substituents (σ > 0.43). Reductive elimination is accelerated by electron-donating substituents (ρ = -2.0) on one or both rings, with the individual σ-values being additive in nature. Longer and more flexible tethers between the two aryl rings result in faster reductive elimination from Ar-Au(X)-Ar and lead to the ?-complexation of the arene by Ar-AuX2 becoming the turnover-limiting step.
Ball, Liam T.,Corrie, Tom J. A.,Lloyd-Jones, Guy C.,Russell, Christopher A.
supporting information
p. 245 - 254
(2021/09/04)

Sterically congested phosphonium borate acids as effective Br?nsted acid catalysts
Phosphonium borate acids [HPPh2(C6F5)][B(C6F5)4] (2), [HPMes2(C6F5)][B(C6F5)4] (3) and [HPMes(C6F5)2][B(C6F5)4] (4) were synthesized via heterolytic dihydrogen cleavage in the presence of triisopropylsilylium and characterized by spectroscopic and crystallographic methods. Br?nsted acid catalysis using compounds 2–4 proved to be efficient for a number of challenging reactions (namely ionic hydrogenation, hydroamination and hydroarylation), owing to the restrained nucleophilicity of the sterically hindered conjugate bases. Reactivity of compounds 2–4 suggests that their pKavalues are similar to that of diethyl oxonium acid.
Sinha, Arup,Jaiswal, Amit K.,Young, Rowan D.
p. 36 - 43
(2016/12/06)

Improving the selectivity in hydrocracking of phenanthrene over mesoporous Al-SBA-15 based Fe-W catalysts by enhancing mesoporosity and acidity
Catalysts for heavy oil hydrocracking require an enhanced mesoporosity (higher pore diameters) and a moderate acidic function (mild acidity) to treat the bulky molecules present in this kind of feedstock and to yield middle distillates (MD). In this work, we have synthesized five different kinds of mesoporous silica based on SBA-15 by modifying some of the variables of their synthesis with the aim at enhancing mesoporosity. NH4F and 1,3,5-trimethylbenzene (TMB) were used to modify the mesostructured arrangement in SBA-15. TMB modified SBA-15 materials exhibited the highest textural properties (2.16 cm3 g-1 and 17 nm) in comparison to NH4F modified silica (1.90 cm3 g-1 and 10.8 nm) and pristine SBA-15 silica (1.03 cm3 g-1 and 12 nm). The acidity of the SBA-15 based materials was modified by a post-synthesis "grafting procedure" to Si/Al molar ratios of 10, 25, and 40. SBA-15 based materials modified with both Al and TMB were used as supports for Fe-W sulfides. These catalysts were tested in the hydrocracking of phenanthrene. In general, all of the catalysts supported on Al-SBA-15 based materials were selective to the ring opening reaction of phenanthrene in contrast to the results obtained over a commercial Ni-Mo/γ catalyst. Such trend was associated to the presence of Br?nsted acid sites on the surface of the Al modified supports as shown 27 Al MAS NMR analysis.
Restrepo-Garcia, Jonatan R.,Baldovino-Medrano, Víctor G.,Giraldo, Sonia A.
p. 98 - 109
(2015/11/28)

Mesoporous zeolite-supported metal sulfide catalysts with high activities in the deep hydrogenation of phenanthrene
Developing highly active hydrogenation catalysts for deep aromatics saturation is of great importance in the production of ultraclean diesel fuel at a low cost. Toward this goal, we synthesized a mesoporous zeolite ZSM-5 (MZSM-5) that was cost-effective and available on a large scale, and used it as a support for the preparation of highly efficient metal sulfide catalysts (NiMoS/MZSM-5 and CoMoS/MZSM-5) for the deep hydrogenation of phenanthrene. The intrinsic activity of the NiMoS/MZSM-5 catalyst (7.4 × 10-4 mol kg-1 s-1) was much higher than that of the alumina-supported NiMo catalyst (NiMoS/γ-Al2O3, 4.8 × 10-4 mol kg-1 s-1), and the selectivity of the deep hydrogenation products over NiMoS/MZSM-5 (20.9%) was higher than for NiMoS/γ-Al2O3 (15.2%). Compared with γ-Al2O3, the relatively weak metal-support interaction could facilitate the formation of polymolybdates on MZSM-5. After sulfidation, the more multistacked MoS2 active phases were formed on the MZSM-5, enhancing the hydrogenation activity of the NiMoS/MZSM-5 catalyst.
Fu, Wenqian,Zhang, Lei,Wu, Dongfang,Xiang, Mei,Zhuo, Qian,Huang, Kai,Tao, Zhongdong,Tang, Tiandi
p. 423 - 433
(2015/09/02)

Understanding Ni Promotion of MoS2/γ-Al2O3 and its Implications for the Hydrogenation of Phenanthrene
The chemical composition and structure of NiMo sulfides supported on γ-Al2O3 and its properties for hydrogenation of polyaromatic compounds is explored. The presence of Ni favors the formation of disperse octahedrally coordinated Mo in the oxide precursors and facilitates its reduction during sulfidation. This decreases the particle size of MoS2 (measured by transmission electron microscopy) and increases the concentration of active sites up to a Ni/(Mo+Ni) atomic ratio of 0.33. At higher Ni loadings, the size of the MoS2 did not decrease further, although the concentration of adsorption sites and accessible Ni atoms decreased. This is attributed to the formation of NiSx clusters at the edges of MoS2. Nickel also interacts with the support, forming separated NiSx clusters, and is partially incorporated into the γ-Al2O3, forming a Ni-spinel. The hydrogenation of phenanthrene follows two pathways; by adding one or two H2 molecules, 9,10-dihydrophenanthrene or 1,2,3,4-tetrahydrophenanthrene are formed as primary products. Only symmetric hydrogenation, leading to 9,10-dihydrophenanthrene, was observed on unpromoted MoS2/γ-Al2O3. In contrast, symmetric and deep hydrogenation (leading to 9,10-dihydrophenanthrene and 1,2,3,4-tetrahydrophenanthrene, respectively) occur with similar selectivity on Ni-promoted MoS2/γ-Al2O3. The rates of both pathways increase linearly with the concentration of Ni atoms in the catalyst. The higher rates for symmetric hydrogenation are attributed to increasing concentrations of reactive species at the surface, and deep hydrogenation is concluded to be catalyzed by Ni at the edge of MoS2 slabs. Well, everybody knows that Ni is the word: In promoted MoS2/γ-Al2O3, Ni substitutes Mo at the perimeter of the MoS2 slabs, forming particles of Ni sulfides with varying sizes at the edges of MoS2 or on the support. The proportions of these species depend on the Ni content. Ni-substituted sites perform faster and deeper hydrogenation of phenanthrene than non-promoted sites.
Schachtl, Eva,Zhong, Lei,Kondratieva, Elena,Hein, Jennifer,Gutiérrez, Oliver Y.,Jentys, Andreas,Lercher, Johannes A.
p. 4118 - 4130
(2015/12/26)

Selective catalytic hydrogenation of polycyclic aromatic hydrocarbons promoted by ruthenium nanoparticles
Ru nanoparticles stabilised by PPh3 are efficient catalysts for hydrogenation of polycyclic aromatic hydrocarbons (PAHs) containing 2-4 rings under mild reaction conditions. These compounds were partially hydrogenated with good to excellent selectivities just by optimizing the reaction conditions. The influence of the nature of substituents present in different positions of naphthalene on the selectivity of hydrogenation was also studied. Hydrogenation of products containing substituents at position 1 is slower than that of products containing substituents at position 2. In all cases, hydrogenation takes place mainly on the less substituted ring.
Bresó-Femenia, Emma,Chaudret, Bruno,Castillón, Sergio
p. 2741 - 2751
(2015/05/27)

Nickel-catalyzed reductive cyclization of alkyl dihalides
The reductive coupling protocol to intramolecular cyclization of dihaloalkanes is presented. It leads to five- and six-membered rings, with the former being more efficient. The incorporation of secondary alkyl halides generally promotes coupling efficiency. To the best of our knowledge, this is the first catalytic ring-closure reaction arising from dihaloalkanes under chemical reductive conditions.
Xue, Weichao,Xu, Hailiang,Liang, Zhuye,Qian, Qun,Gong, Hegui
supporting information
p. 4984 - 4987
(2014/12/11)

Cycloaddition reactions of benzyne with olefins
Some novel cycloaddition reactions based on benzyne and olefins have been developed. These reactions were performed in the absence of a transition metal catalyst, and they displayed good yields. These cycloaddition reactions of benzyne with olefins provid
Chen, Zhao,Han, Xie,Liang, Jin-Hua,Yin, Jun,Yu, Guang-Ao,Liu, Sheng-Hua
p. 1535 - 1539
(2015/01/09)

Efficient synthesis of 9-aryldihydrophenanthrenes by a cascade reaction involving arynes and styrenes
A mild, general, and transition-metal-free protocol for the synthesis of 9,10-dihydrophenanthrenes is reported. The aryne generated by the fluoride-induced 1,2-elimination of 2-(trimethylsilyl)aryl triflates undergoes an efficient cascade reaction initiated by the Diels-Alder reaction with the differently substituted styrenes leading to the formation of 9-aryl-9,10-dihydrophenanthrene derivatives in moderate to good yields.
Bhojgude, Sachin Suresh,Bhunia, Anup,Gonnade, Rajesh G.,Biju, Akkattu T.
supporting information
p. 676 - 679
(2014/03/21)

Metal-halogen exchange between hydrazine polyanions and α,α′-dibromo-o-xylene
Aromatic-bridged bis(hydrazines) were found to be the main products in the reaction of hydrazine polyanions with α,α′-dibromo-o-xylene. It was confirmed that the reaction is driven by a metal-halogen exchange process. A three-step reaction mechanism is suggested.
Lebedev, Oleg,Maeeorg, Uno
p. 188 - 193
(2014/02/14)

Quenched skeletal Ni as the effective catalyst for selective partial hydrogenation of polycyclic aromatic hydrocarbons
Quenched skeletal Ni is an active and selective catalyst for selective partial hydrogenation of polycyclic aromatic hydrocarbons (PAHs). The molecular structure of PAHs significantly dominate the hydrogenation process and furthermore, the distribution of hydrogenated products.
Liu, Chengyun,Rong, Zeming,Sun, Zhuohua,Wang, Yong,Du, Wenqiang,Wang, Yue,Lu, Lianhai
p. 23984 - 23988
(2013/11/19)

Iron-catalyzed homocoupling of aryl halides and derivatives in the presence of alkyllithiums
Direct synthesis of biaryl derivatives from aryl halides takes place under very mild temperature conditions by using a ligand-free iron catalytic system. The procedure, which proceeds via an in situ quantitative aryl halide exchange with alkyllithiums, allows for excellent control of the reactivity and is in line with the sustainable development. The method is also applicable to styryl and benzyl halides and to phenylacetylene.
Toummini, Dounia,Ouazzani, Fouad,Taillefer, Marc
supporting information
p. 4690 - 4693
(2013/10/08)

Photoredox transformations with dimeric gold complexes
Let the sunshine in! Unactivated alkyl and aryl bromides underwent a light-enabled reductive radical cyclization in the presence of a dimeric phosphine-gold complex as a photocatalyst (see scheme; X=C(CO 2Et)2, NR, O). Sunlight can be used as the energy source for this simple and efficient radical reaction, which does not require potentially hazardous and toxic chemical reagents, such as organostannanes and chemical initiators.
Revol, Guillaume,McCallum, Terry,Morin, Mathieu,Gagosz, Fabien,Barriault, Louis
supporting information
p. 13342 - 13345
(2014/01/06)

Gold-catalyzed cyclizations of cis-enediynes: Insights into the nature of gold-aryne interactions
Golden aryne? Gold aryne complexes are inferred as transition states in dual gold-catalyzed cyclizations of cis-enediynes (see scheme; DCE=1,2-dichloroethane). They are better described as ortho-aurophenyl cations, which react with weak nucleophiles and undergo facile intramolecular insertions into C(sp3)-H bonds. Indanes, fused heteroarenes, and phenol derivatives are readily prepared using this method. Copyright
Wang, Youliang,Yepremyan, Akop,Ghorai, Subir,Todd, Robert,Aue, Donald H.,Zhang, Liming
supporting information
p. 7795 - 7799
(2013/08/23)

Potassium tert-butoxide promoted intramolecular arylation via a radical pathway
Potassium tert-butoxide mediated intramolecular cyclization of aryl ethers, amines, and amides was efficiently performed under microwave irradiation to provide the corresponding products in high regioisomeric ratios. The reaction proceeds via single-electron transfer to initiate the formation of an aryl radical, followed by a kinetically favored 5-exo-trig and subsequent ring expansion.
Roman, Daniela Sustac,Takahashi, Yoko,Charette, Andre B.
supporting information; experimental part
p. 3242 - 3245
(2011/08/02)

Neocuproine-KOtBu promoted intramolecular cross coupling to approach fused rings
Polycycles can be produced with different linkages (A, B = O, N, C, S) by constructing biaryl C-C bonds via neocuproine-KOtBu promoted cross coupling between C-Xs and C-Hs.
Sun, Chang-Liang,Gu, Yi-Fan,Huang, Wei-Ping,Shi, Zhang-Jie
supporting information; experimental part
p. 9813 - 9815
(2011/10/11)

Reduction of polycyclic aromatic hydrocarbons promoted by cobalt or manganese nanoparticles
A new methodology for the partial reduction of polycyclic aromatic and heteroaromatic hydrocarbons under mild reaction conditions is presented, the process being a reasonable alternative to the catalytic hydrogenation or the Birch reaction. The reduction protocol described is based on the use of cobalt or manganese nanoparticles generated in situ in a simple and economic way, by reduction of commercially available CoCl2·6H2O or MnCl2·2H2O in the presence of lithium sand and the corresponding PAH, acting itself as an electron carrier. The use of a deuterium-oxide-containing cobalt(II) salt allows the simple preparation of deuterium labeled products. The regiochemistry and degree of reduction in the case of 1-substituted naphthalene derivatives markedly depends on the nature of the metal-NPs used.
Nador, Fabiana,Moglie, Yanina,Vitale, Cristian,Yus, Miguel,Alonso, Francisco,Radivoy, Gabriel
experimental part
p. 4318 - 4325
(2010/07/09)

Birch reductions at room temperature with alkali metals in silica gel (Na2K-SG(I))
(Chemical Equation Presented) Alkali metals in silica gel (the Na 2K-SG(I) reagent) cleanly effect Birch reductions of substrates with at least two or more aromatic rings. The reaction conditions are alcohol-free, ammonia-free, and achieve excellent yields and high selectivities at room temperature.
Nandi, Partha,Dye, James L.,Jackson, James E.
supporting information; experimental part
p. 5790 - 5792
(2010/01/06)

Ammonia-free Birch reductions with sodium stabilized in silica gel, Na-SG(I)
Ammonia-free Birch reduction conditions were developed based upon sodium stabilized in silica gel for a variety of substrates. In general, the yields were similar to those reported for lump sodium in liquid ammonia.
Costanzo, Michael J.,Patel, Mitul N.,Petersen, Kathryn A.,Vogt, Paul F.
supporting information; experimental part
p. 5463 - 5466
(2010/01/11)

Hydroxide ion as electron source for photochemical Birch-type reduction and photodehalogenation
The photochemical Birch-type reduction of arenes and the photodehalogenation of haloarenes by a hydroxide ion that acted as an electron source occurred in 2-PrOH. The efficiency of these photoreactions was dependent on the nature of the substrate, the concentration of NaOH, and the solvent used. These photoreactions provide an environmentally friendly method for the reduction of aromatic rings and dehalogenation.
Yoshimi, Yasuharu,Ishise, Akihiro,Oda, Hiromu,Moriguchi, Yousuke,Kanezaki, Hiroki,Nakaya, Yukari,Katsuno, Kayoko,Itou, Tatsuya,Inagaki, Sho,Morita, Toshio,Hatanaka, Minoru
p. 3400 - 3404
(2008/09/21)

Novel and rapid palladium-assisted 6π electrocyclic reaction affording 9,10-dihydrophenanthrene and its analogues
(Equation Presented) A novel methodology for the synthesis of 9,10-dihydrophenanthrene and its analogues has been developed via a palladium-assisted 6π electrocyclic reaction followed by formaldehyde elimination.
Jana, Rathin,Chatterjee, Indranil,Samanta, Shubhankar,Ray, Jayanta K.
supporting information; experimental part
p. 4795 - 4797
(2009/05/07)

Reductive hydrogenation of polycyclic aromatic hydrocarbons catalyzed by metalloporphyrins
The hydrogenation of polycyclic aromatic hydrocarbons (PAHs) (naphthalene, anthracene, and phenanthrene) catalyzed by metalloporphyrins based on cobalt, nickel or iron was studied in aqueous solutions at room temperature and ambient pressure. Nickel porphyrin (P1) activated by nanosized zero-valent iron (nano-ZVI) and cobalt porphyrins (P2) and (P4) activated by titanium(III) citrate as the electron donor were demonstrated to be promising catalysts for the reductive hydrogenation of PAHs. In particular, partially saturated di-, tetra-, and octahydrogenated products were obtained for anthracene or phenanthrene using a nickel porphyrin activated by nano-ZVI, while naphthalene was transformed to tetralin. Systems containing cobalt porphyrins activated by titanium(III) citrate exhibited a high selectivity and activity toward hydrogenation of anthracene, producing 9,10-dihydroanthracene. However, no formation of hydrogenated hydrocarbons was observed from naphthalene or phenanthrene using cobalt porphyrins.
Nelkenbaum, Elza,Dror, Ishai,Berkowitz, Brian
p. 210 - 217
(2008/02/04)

Nickel-catalyzed carboannulation reaction of o-bromobenzyl zinc bromide with unsaturated compounds
(Chemical Equation Presented) A number of indenes have been prepared in good yields by treating o-bromobenzyl zinc bromide 1 with various terminal and internal alkynes in the presence of a nickel catalyst. The nickel-catalyzed carboannulation reaction was successfully extended to the synthesis of indane derivatives by reaction of 1 with acrylates and styrene.
Deng, Ruixue,Sun, Liangdong,Li, Zhi
p. 5207 - 5210
(2008/09/17)

Estimating the limiting reducing power of SmI2/H 2O/amine and YbI2/H2O/amine by efficient reduction of unsaturated hydrocarbons
The mixture of samarium diiodide, amine, and water (SmI2/H 2O/Et3N) is known to be a particularly powerful reductant, but until now the limiting reducing power has not been determined. A series of unsaturated hydrocarbons with varying half-wave reduction potentials (E 1/2 = -1.6 to -3.4 V, vs SCE) have been treated with SmI 2/H2O/Et3N and YbI2/H 2O/Et3N, respectively. All hydrocarbons with potentials of -2.8 V or more positive were readily reduced with SmI2/H 2O/Et3N, whereas all hydrocarbons with potentials of -2.3 V or more positive were readily reduced using YbI2/H 2O/Et3N. This defines limiting values of the chemical reducing power of SmI2/H2O/Et3N to -2.8 V and of YbI2/H2O/Et3N to -2.3 V vs SCE.
Dahlen, Anders,Nilsson, Ake,Hilmersson, Goeran
p. 1576 - 1580
(2007/10/03)

Iron-catalyzed homo-coupling of simple and functionalized arylmagnesium reagents
(Chemical Equation Presented) Iron-catalyzed homo-coupling of simple and functionalized arylmagnesium reagents is described. The reaction is highly chemoselective (CN, COOEt and NO2 groups are tolerated). The procedure was used to perform intramolecular couplings. This cyclization reaction is the key step of the total synthesis of the N-methylcrinasiadine.
Cahiez, Gerard,Chaboche, Christophe,Mahuteau-Betzer, Florence,Ahr, Mathieu
p. 1943 - 1946
(2007/10/03)

Flow-vacuum pyrolysis of polycyclic compounds. 221 : Pyrolysis of 2,2'-bis(hydroxymethyl)biphenyl
The flow-vacuum pyrolysis of the title diol, between 600°C - 800°C and 1mm Hg in argon atmosphere, was investigated using GC/MS. The main reaction products were: fluorene, 9-methylfluorene, 9-methylenefluorene; 9,10-dihydrophenanthrene; phenanthrene; 9-hydroxy-9,10-dihydroanthracene; 9-fluorenol; 9-fluorenone; 2-methyl-2'-formylbiphenyl (major product; 38% at 850°C); 2-hydroxymethyl-2'-formylbiphenyl and 2,2'-diphendialdehyde. The amount of products resulted from intramolecular cyclization was 52% at 850°C and the ratio between products with five-member and six-member central ring was 39:13 at 850°C. A radical mechanism explaining the formation of the reaction products is suggested and a comparison between pyrolysis of the title diol and of the previously studied 2,2'-bis(bromomethyl)biphenyl is made.
Istrati, Daniela,Marton, George,Drǎghici, Constantin,Grigore, Adriana,Banciu, Mircea D.
p. 719 - 724
(2007/10/03)

Semivolatile and volatile compounds in combustion of polyethylene
The evolution of semivolatile and volatile compounds in the combustion of polyethylene (PE) was studied at different operating conditions in a horizontal quartz reactor. Four combustion runs at 500 and 850°C with two different sample mass/air flow ratios and two pyrolytic runs at the same temperatures were carried out. Thermal behavior of different compounds was analyzed and the data obtained were compared with those of literature. It was observed that α,ω-olefins, α-olefins and n-paraffins were formed from the pyrolytic decomposition at low temperatures. On the other hand, oxygenated compounds such as aldehydes were also formed in the presence of oxygen. High yields were obtained of carbon oxides and light hydrocarbons, too. At high temperatures, the formation of polycyclic aromatic hydrocarbons (PAHs) took place. These compounds are harmful and their presence in the combustion processes is related with the evolution of pyrolytic puffs inside the combustion chamber with a poor mixture of semivolatile compounds evolved with oxygen. Altogether, the yields of more than 200 compounds were determined. The collection of the semivolatile compounds was carried out with XAD-2 adsorbent and were analyzed by GC-MS, whereas volatile compounds and gases were collected in a Tedlar bag and analyzed by GC with thermal conductivity and flame ionization detectors.
Font, Rafael,Aracil, Ignacio,Fullana, Andrés,Conesa, Juan A.
p. 615 - 627
(2007/10/03)

Biaryl synthesis via direct arylation: Establishment of an efficient catalyst for intramolecular processes
In this Communication, we describe direct arylation reactions with improved scope and catalyst activity for the intramolecular formation of biaryl compounds. This was achieved through the establishment of a highly active and robust catalyst system and the subsequent development of a novel phosphine ligand 27. The enhanced catalytic activity extends these transformations to include previously unreactive and poorly reactive substrates, and allows for very low catalyst loadings to be employedas little as 0.1 mol %. Copyright
Campeau, Louis-Charles,Parisien, Mathieu,Leblanc, Melissa,Fagnou, Keith
p. 9186 - 9187
(2007/10/03)

Recoverable, Reusable, Highly Active, and Sulfur-Tolerant Polymer Incarcerated Palladium for Hydrogenation
A new type of immobilized palladium, PI (polymer incarcerated) Pd (2b), from Pd(PPh3)4 and copolymer (1b) has been developed. The excellent activity of PI Pd has been demonstrated in hydrogenation of various olefins, benzyl ethers, and nitro and aromatic compounds. PI Pd is tolerant under high pressure and high temperature and can be recovered and reused several times without loss of activity even under harsh conditions. Moreover, PI Pd is highly resistant to poisoning by sulfur.
Okamoto, Kuniaki,Akiyama, Ryo,Kobayashi, Shu
p. 2871 - 2873
(2007/10/03)

Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
p. 402 - 415
(2007/10/03)

Symmetry-enforced conformational control of photochemical reactivity in 2-vinyl-1,3-terphenyl
The photocyclization of o-vinylbiphenyl to 9,10-dihydrophenanthrene occurs with very low quantum yield because of the low ground-state population of the reactive syn rotamer. 2-Vinyl-1,3-terphenyl exists as a single rotamer which undergoes highly efficient photocyclization. Irradiation at 77 K in a rigid glass permits observation of the 8a,9-dihydrophenanthrene which rearranges to the 9,10-dihydrophenanthrene upon warming of the glass. The barriers for photocyclization and the thermal sigmatropic hydrogen shift are both remarkably small. Copyright
Lewis, Frederick D.,Zuo, Xiaobing,Gevorgyan, Vladimir,Rubin, Michael
p. 13664 - 13665
(2007/10/03)