- SnCl2-catalyzed synthesis of carbamates from renewable origin alcohols
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Effects of structure and reactivity of renewable origin alcohols in the conversion and selectivity of the SnCl2-catalyzed reactions in the presence and absence of urea were assessed. Convenient simple and suitable method for the synthesis of carbamates from renewable origin alcohols and urea in one-step are provided. We have assessed the activity of SnCl2 catalyst, a commercially affordable Lewis acid, in reactions of urea alcoholysis with different natural origin alcohols (geranyl, neryl, bornyl, cinnamyl, α-terpinyl and benzyl alcohols), aiming to synthesize carbamates, which are biologically active compounds, building blocks in organic synthesis and raw material to synthesize polyurethanes. The low cost of urea, the water tolerant catalyst and phosgene free reaction are positive aspects of this carbamates synthesis process. The different reaction pathways were assessed. A mechanism was proposed based on FT-IR experiments and experimental data.
- da Silva, Márcio José,Chaves, Diego Morais
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p. 1169 - 1180
(2019/01/28)
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- A comparative study on the gas-phase and liquid-phase thermal isomerization reaction of α-pinene
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In this paper, a method of preparation of ocimene is investigated, which is obtained from isomerization reaction of α-pinene. Two kinds of experimental apparatus are established for the investigation of the thermal isomerization reaction of α-pinene. The behavior of thermal isomerization reaction of α-pinene is respectively discussed in the gas phase and in the liquid phase. Under gas phase conditions, the conversion of α-pinene is 80% and the selectivity of ocimene is 30%-33%. Under liquid phase conditions, the conversion of α-pinene is 60% and the selectivity of ocimene is 50%-54%. According to the kinetic-molecular theory of ideal gases, two kinds of reaction models are proposed to visualize the reaction process. In addition, the mechanism and kinetics of thermal isomerization reaction of α-pinene are respectively discussed. The conclusion is that the gas phase reaction temperature is calculated to be 390-450 °C and the liquid phase reaction temperature is calculated to be 450-550°C. From a bond dissociation energy point of view, results support the hypothesis that the reaction involves biradical intermediates. Copyright
- He, Jindong,Gong, Yan,Zhao, Wentao,Tang, Xiangyang,Qi, Xin
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- A 1,6-ring closure mechanism for (+)-δ-cadinene synthase?
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Recombinant (+)-δ-cadinene synthase (DCS) from Gossypium arboreum catalyzes the metal-dependent cyclization of (E,E)-farnesyl diphosphate (FDP) to the cadinane sesquiterpene δ-cadinene, the parent hydrocarbon of cotton phytoalexins such as gossypol. In contrast to some other sesquiterpene cyclases, DCS carries out this transformation with >98% fidelity but, as a consequence, leaves no mechanistic traces of its mode of action. The formation of (+)-δ-cadinene has been shown to occur via the enzyme-bound intermediate (3R)-nerolidyl diphosphate (NDP), which in turn has been postulated to be converted to cis-germacradienyl cation after a 1,10-cyclization. A subsequent 1,3-hydride shift would then relocate the carbocation within the transient macrocycle to expedite a second cyclization that yields the cadinenyl cation with the correct cis stereochemistry found in (+)-δ-cadinene. An elegant 1,10-mechanistic pathway that avoids the formation of (3R)-NDP has also been suggested. In this alternative scenario, the final cadinenyl cation is proposed to be formed through the intermediacy of trans, trans-germacradienyl cation and germacrene D. In addition, an alternative 1,6-ring closure mechanism via the bisabolyl cation has previously been envisioned. We report here a detailed investigation of the catalytic mechanism of DCS using a variety of mechanistic probes including, among others, deuterated and fluorinated FDPs. Farnesyl diphosphate analogues with fluorine at C2 and C10 acted as inhibitors of DCS, but intriguingly, after prolonged overnight incubations, they yielded 2F-germacrene(s) and a 10F-humulene, respectively. The observed 1,10-, and to a lesser extent, 1,11-cyclization activity of DCS with these fluorinated substrates is consistent with the postulated macrocyclization mechanism(s) en route to (+)-δ-cadinene. On the other hand, mechanistic results from incubations of DCS with 6F-FPP, (2Z,6E)-FDP, neryl diphosphate, 6,7-dihydro-FDP, and NDP seem to be in better agreement with the potential involvement of the alternative biosynthetic 1,6-ring closure pathway. In particular, the strong inhibition of DCS by 6F-FDP, coupled to the exclusive bisabolyl- and terpinyl-derived product profiles observed for the DCS-catalyzed turnover of (2Z,6E)-farnesyl and neryl diphosphates, suggested the intermediacy of α-bisabolyl cation. DCS incubations with enantiomerically pure [1- 2H1](1R)-FDP revealed that the putative bisabolyl-derived 1,6-pathway proceeds through (3R)-nerolidyl diphosphate (NDP), is consistent with previous deuterium-labeling studies, and accounts for the cis stereochemistry characteristic of cadinenyl-derived sesquiterpenes. While the results reported here do not unambiguously rule in favor of 1,6- or 1,10-cyclization, they demonstrate the mechanistic versatility inherent to DCS and highlight the possible existence of multiple mechanistic pathways.
- Faraldos, Juan A.,Miller, David J.,Gonzalez, Veronica,Yoosuf-Aly, Zulfa,Cascon, Oscar,Li, Amang,Allemann, Rudolf K.
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supporting information; experimental part
p. 5900 - 5908
(2012/05/07)
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- Kinetic and mechanistic study on the thermal isomerization of ocimene in the liquid phase
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The rate of thermal isomerization of ocimene in the liquid phase has been investigated in the range 90-150°C. The rate constant for the disappearance of ocimene may be expressed by k=1.3×1010e -11994.2/T(min-1), from which we can infer that the activation energy is 99.7kJmol-1 and the pre-exponential factor is 1.3×1010min-1. The half-life for the disappearance of ocimene may be expressed by t1/2=5.2×10-11e 11994.2/T(min). The conclusion has been supported by the study results that the ocimene is safe when temperature is below 100°C. A discussion of the mechanism concerning the conversion is included. Copyright
- He, Jindong,Xie, Meng,Tang, Xiangyang,Qi, Xin
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body text
p. 373 - 378
(2012/07/30)
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- Sesquiterpene synthases Cop4 and Cop6 from Coprinus cinereus: Catalytic promiscuity and cyclization of farnesyl pyrophosphate geometric isomers
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Sesquiterpene synthases catalyze with different catalytic fidelity the cyclization of farnesyl pyrophosphate (FPP) into hundreds of known compounds with diverse structures and stereochemistries. Two sesquiterpene synthases, Cop4 and Cop6, were previously isolated from Coprinus cinereus as part of a fungal genome survey. This study investigates the reaction mechanism and catalytic fidelity of the two enzymes. Cyclization of all-trans-FPP ((E,E)-FPP) was compared to the cyclization of the cis-trans isomer of FPP ((Z,E)-FPP) as a surrogate for the secondary cisoid neryl cation intermediate generated by sesquiterpene synthases, which are capable of isomerizing the C2-C3 π bond of all-trans-FPP. Cop6 is a "high-fidelity" α-cuprenene synthase that retains its fidelity under various conditions tested. Cop4 is a catalytically promiscuous enzyme that cyclizes (E,E)-FPP into multiple products, including (-)-germacrene D and cubebol. Changing the pH of the reaction drastically alters the fidelity of Cop4 and makes it a highly selective enzyme. Cyclization of (Z,E)-FPP by Cop4 and Cop6 yields products that are very different from those obtained with (E,E)-FPP. Conversion of (E,E)-FPP proceeds via a (6R)-β-bisabolyl carbocation in the case of Cop6 and an (E,E)-germacradienyl carbocation in the case of Cop4. However, (Z,E)-FPP is cyclized via a (6S)-β-bisabolene carbocation by both enzymes. Structural modeling suggests that differences in the active site and the loop that covers the active site of the two enzymes might explain their different catalytic fidelities.
- Lopez-Gallego, Fernando,Agger, Sean A.,Abate-Pella, Daniel,Distefano, Mark D.,Schmidt-Dannert, Claudia
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scheme or table
p. 1093 - 1106
(2011/03/20)
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- Mechanistic and kinetic insights into the thermally induced rearrangement of α-pinene
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(Chemical Equation Presented) The thermal rearrangement of α-pinene (1) is interesting from mechanistic as well as kinetic point of view. Carrier gas pyrolyses with 1 and its acyclic isomers ocimene (2) and alloocimene (3) were performed to investigate the thermal network of these hydrocarbons. Kinetic analysis of the major reaction steps allows for a deeper insight in the reaction mechanism. Thus it was possible to explain the racemization of 1, the formation of racemic limonene (4), and the absence of the primary pyrolysis product 2 in the reaction mixture resulting from thermal rearrangement of 1. Results supported the conclusion that the reactions starting with 1 involve biradical transition states.
- Stolle, Achim,Ondruschka, Bernd,Findeisen, Matthias
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supporting information; scheme or table
p. 8228 - 8235
(2009/04/11)
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- Comprehensive kinetic and mechanistic considerations for the gas-phase behaviour of pinane-type compounds
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The thermal behaviour of selected pinane-type compounds, α-pinene (1), β-pinene (2), pinane (3) and nopinone (4), has been investigated. The conversion of the bicyclic starting materials to their acyclic and monocyclic isomers as well as the consecutive reactions of the acyclic main isomerisation products are discussed. The conversion of 1-4 in a reaction network is presented and the experimental evidence for the formation of pyrolysis products by a biradical pathway is discussed. In addition to these results a kinetic model describing the isomerisation of the bicyclic compounds to their acyclic and monocyclic isomers is presented. A good correlation between kinetic simulations and experimental data is revealed. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Stolle, Achim,Ondruschka, Bernd,Bonrath, Werner
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p. 2310 - 2317
(2008/02/08)
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- Zeolite Assisted Dehydration of Terpenic Alcohols : Convenient Synthesis of 1,3-Dienes and Oxepane
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Terpenic alcohols undergo facile dehydration over H-ZSM-5 to yield 1,3-dienes, such as farnesenes, ocimene, myrcene and isoprene. Studies on homoallylic alcohol (1e) gave oxepane (2e).
- Reddy, P. Veera,Bhat, Sujata V.
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p. 688 - 689
(2007/10/03)
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- Chlorotrimethylsilane catalysed acetylation of alcohols
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A variety of alcohols are converted into the corresponding acetates upon treatment with acetic anhydride and catalytic amount of chlorotrimethylsilane in acetonitrile (or dichloromethane).
- Kumareswaran,Gupta, Anuradha,Vankar, Yashwant D.
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p. 277 - 282
(2007/10/03)
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- Molybdenum- and tungsten-catalyzed allylation of aromatic compounds with allylic esters and alcohols
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A novel method to substitute aromatic compounds with allylic groups using oxygen-containing allylic compounds in the presence of molybdenum or tungsten carbonyls under neutral conditions has been developed. The method is applicable to one step synthesis of methyl eugenol.
- Shimizu, Isao,Sakamoto, Toshiaki,Kawaragi, Saeko,Maruyama, Yooichiro,Yamamoto, Akio
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p. 137 - 138
(2007/10/03)
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- Photochemical Transformations VI: Organic Iodides (Part 5) - Templet Effect of Transition Metal Ions on Photocyclization of Some Olefinic Acyclic Terpene Iodides
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Photocyclization of citronellyl iodide in the presence of certain transition metal salts especially CuCl, results in a significant increase (from 16percent to 35percent) in the yield of the cyclization products.Similar results have been obtained with geranyl and neryl iodides (11, 17).This enhancement of cyclization/elimination ratio is sought to be explained in terms of a templet effect of the transition metal ion.
- Subbarao, Kanury V.,Damodaran, N. P.,Dev, Sukh
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p. 1008 - 1011
(2007/10/02)
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- 2-Allylisourea as an Effective Agent for Direct α-Allylation of Ketone and Aldehyde Assisted by Palladium(0) under Neutral Conditions
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Direct α-allylation of a variety of ketones and aldehydes with 2-allylisourea took place in the presence of a catalytic amount of a palladium(0) complex under neutral and mild conditions.Scope and limitations of this novel method have been investigated.
- Inoue, Yoshio,Toyofuku, Masanori,Taguchi, Masaaki,Okada, Shin-ichi,Hashimoto, Harukichi
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p. 885 - 892
(2007/10/02)
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- COPPER INDUCED SOLVOLYSIS OF SULFUR COMPOUNDS
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The displacement of a phenylthio group by an acetate ion some allylic or α-alcoxy sulfides and thioacetals was cleanly performed by treating them with a mixture of copper powder and cupric acetate in acetic acid.
- Uguen, D.
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p. 541 - 542
(2007/10/02)
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- PHOTOCHEMICAL TRANSFORMATIONS-III; ORGANIC IODIDES (Part 3): GERANYL AND NERYL IODIDES AND 2(E),6(E)- AND 2(Z),6(E)-FARNESYL IODIDES
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Solution photolysis of geranyl and neryl iodides, and 2(E),6(E)- and 2(Z),6(E)-farnesyl iodides has been carried out.Products arising from simple elimination as well as ?-participation are formed.Thus, both geranyl and neryl iodides furnished, besides some unidentified compounds, myrcene, cis-ocimene, limonene and terpinolene, though in different proportions.Likewise, the sesquiterpene analogues yielded different amounts of trans-β-farnesene, β-bisabolene, trans-α-bisabolene and ar-curcumene.Results have been discussed in terms of ionic intermediates.
- Saplay, K. M.,Damodaran, N. P.,Dev, Sukh
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p. 2999 - 3004
(2007/10/02)
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- PYROLYSIS OF 2-ALLYLOXYTROPONES: A NEW ELIMINATION RECTION TO TERMINAL DIENES
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By pyrolysis over 140 deg C, several 2-alkenyloxytropones gave terminal dienes and regenerated tropolones.The elimination proceeded in the electrocyclic 6?+2?+2?-mode on the Claisen intermediates.This was applied to a synthesis of thujopsadiene.
- Takeshita, Hitoshi,Mametsuka, Hiroaki,Uchida, Kingo
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p. 1061 - 1064
(2007/10/02)
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- REARRANGEMENTS OF MONOTERPENES IN FUSED ORGANIC ACID
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Rearrangements of terpenic alcohols are significantly influenced by the nature of the organic acid used as the reaction medium.The formation of neoisothujyl alcohol is a highly favoured process in abietic acid.
- Angelis, Francesco De,Ferretti, Gabriella,Botta, Maurizio,Nicoletti, Rosario
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p. 499 - 500
(2007/10/02)
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