1856-63-9Relevant academic research and scientific papers
Easy access to (E) β-ocimene
Yildizhan, Selma,Schulz, Stefan
, p. 2831 - 2833 (2011)
β-Ocimene is one of the most common monoterpenes found in Nature, but a simple and reliable synthesis of the pure E-isomer has been missing. Here, we report a simple procedure involving a Grignard coupling as the key step that allows its synthesis on gram scales. The configuration of the double bond is fixed in the starting material. Georg Thieme Verlag Stuttgart · New York.
Silver nanoparticle-Catalyzed diels-alder cycloadditions of 2′-hydroxychalcones
Cong, Huan,Becker, Clinton F.,Elliott, Sean J.,Grinstaff, Mark W.,Porco Jr., John A.
, p. 7514 - 7518 (2010)
Metal nanoparticles are currently being employed as catalysts for a number of classical chemical transformations. In contrast, identification of novel reactions of nanoparticles, especially toward the synthesis of complex natural products and derivatives, is highly underdeveloped and represents a bourgeoning area in chemical synthesis. Herein, we report silica-supported silver nanoparticles as solid, recyclable catalysts for Diels-Alder cycloadditions of 2′-hydroxychalcones and dienes in high yield and turnover number. The use of silver nanoparticle catalysts is further demonstrated by the total synthesis of the cytotoxic natural product panduratin A employing a highly electron-rich dienophile and Lewis acid sensitive diene.
A donor-acceptor complex enables the synthesis of: E -olefins from alcohols, amines and carboxylic acids
Chen, Kun-Quan,Shen, Jie,Wang, Zhi-Xiang,Chen, Xiang-Yu
, p. 6684 - 6690 (2021/05/31)
Olefins are prevalent substrates and functionalities. The synthesis of olefins from readily available starting materials such as alcohols, amines and carboxylic acids is of great significance to address the sustainability concerns in organic synthesis. Metallaphotoredox-catalyzed defunctionalizations were reported to achieve such transformations under mild conditions. However, all these valuable strategies require a transition metal catalyst, a ligand or an expensive photocatalyst, with the challenges of controlling the region- and stereoselectivities remaining. Herein, we present a fundamentally distinct strategy enabled by electron donor-acceptor (EDA) complexes, for the selective synthesis of olefins from these simple and easily available starting materials. The conversions took place via photoactivation of the EDA complexes of the activated substrates with alkali salts, followed by hydrogen atom elimination from in situ generated alkyl radicals. This method is operationally simple and straightforward and free of photocatalysts and transition-metals, and shows high regio- and stereoselectivities.
SnCl2-catalyzed synthesis of carbamates from renewable origin alcohols
da Silva, Márcio José,Chaves, Diego Morais
, p. 1169 - 1180 (2019/01/28)
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.
A comparative study on the gas-phase and liquid-phase thermal isomerization reaction of α-pinene
He, Jindong,Gong, Yan,Zhao, Wentao,Tang, Xiangyang,Qi, Xin
, p. 15 - 22 (2013/03/13)
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
Mechanistic insights into the rhenium-catalyzed alcohol-to-olefin dehydration reaction
Korstanje, Ties J.,Jastrzebski, Johann T. B. H.,Kleingebbink, Robertus J. M.
, p. 13224 - 13234 (2013/10/01)
Rhenium-based complexes are powerful catalysts for the dehydration of various alcohols to the corresponding olefins. Here, we report on both experimental and theoretical (DFT) studies into the mechanism of the rhenium-catalyzed dehydration of alcohols to olefins in general, and the methyltrioxorhenium-catalyzed dehydration of 1-phenylethanol to styrene in particular. The experimental and theoretical studies are in good agreement, both showing the involvement of several proton transfers, and of a carbenium ion intermediate in the catalytic cycle. Ionic or concerted? Rhenium-based complexes are powerful catalysts for the dehydration of various alcohols to the corresponding olefins. Experimental and DFT studies into the mechanism of the rhenium-catalyzed dehydration of alcohols to olefins are reported. The experimental and theoretical studies are in good agreement, both showing the involvement of a carbenium ion intermediate in the catalytic cycle (see figure). Copyright
A 1,6-ring closure mechanism for (+)-δ-cadinene synthase?
Faraldos, Juan A.,Miller, David J.,Gonzalez, Veronica,Yoosuf-Aly, Zulfa,Cascon, Oscar,Li, Amang,Allemann, Rudolf K.
supporting information; experimental part, p. 5900 - 5908 (2012/05/07)
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.
Kinetic and mechanistic study on the thermal isomerization of ocimene in the liquid phase
He, Jindong,Xie, Meng,Tang, Xiangyang,Qi, Xin
body text, p. 373 - 378 (2012/07/30)
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
Cyclization of citronellal in a supercritical solvent in a flow reactor in the presence of Al2O3
Anikeev,Il'Ina,Volcho,Salakhutdinov
, p. 1917 - 1919 (2013/01/15)
The reactivity of citronellal under supercritical solvent conditions in a flow reactor in the presence of Al2O3 is examined. It is shown that at 160°C, the main transformation product of citronellal is isopulegol, and when the temperature is increased to 190°C, they are monoterpenes with a para-menthane framework and myrcene. Pleiades Publishing, Ltd., 2012.
Novel route to a fruitful mixture of terpene fragrances in particular phellandrene starting from natural feedstock geraniol using weak acidic boron based catalyst
Eisenacher, Matthias,Beschnitt, Stefan,H?lderich, Wolfgang
experimental part, p. 214 - 217 (2012/09/08)
Myrcene, ocimene and in particular phellandrene were selectively generated as products by dehydration of the natural feedstock geraniol over a weak acidic boron pentasil zeolite catalyst in a gas phase reaction. Additionally linalool was formed by rearrangement reaction. The total selectivity of these 4 terpenes is up to 99%.
