25086-72-0Relevant academic research and scientific papers
Reaction of Singlet Oxygen with trans-4-Propenylanisole. Formation of [2 + 2] Products with Added Acid
Greer, Alexander,Vassilikogiannakis, Georgios,Lee, Kun-Chun,Koffas, Telly S.,Nahm, Keepyung,Foote, Christopher S.
, p. 6876 - 6878 (2000)
We report the effects of added acid in the reaction of singlet oxygen with trans-4-propenylanisole (1). We provide evidence that solvent acidity modifies the behavior of the transient intermediates. Relative to reactions in aprotic solvent, enhanced dioxetane concentrations are observed in MeOH and in nonprotic solvents with acid. We suggest a new mechanism that invokes a proton transfer from MeOH and benzoic acid to perepoxide (2) and zwitterion (3) intermediates.
Ruthenium(iv) catalysts for the selective estragole to trans-anethole isomerization in environmentally friendly media
Lastra-Barreira, Beatriz,Francos, Javier,Crochet, Pascale,Cadierno, Victorio
, p. 307 - 313 (2011)
Several ruthenium(iv) complexes have been tested as potential catalysts for the isomerization of estragole into anethole using water and glycerol as alternative green reaction media. Best results in terms of activity and E-selectivity were obtained with the dimeric species [{RuCl(μ-Cl) (η3:η3-C10H16)} 2] (C10H16 = 2,7-dimethylocta-2,6-diene-1,8- diyl) and the mononuclear derivative [RuCl2(η3: η3-C10H16){P(OMe)3}]. In particular, using a ruthenium loading of 1 mol%, almost quantitative and stereoselective formation of trans-anethole (trans/cis ratios = 99:1) could be reached at 80°C in short times (5-30 min) employing water-MeOH (EtOH) or glycerol-MeOH (EtOH) mixtures (1:1 v/v) as solvent. Recyclability issues have also been addressed.
Arylsulfonylacetamides as bifunctional reagents for alkene aminoarylation
Monos, Timothy M.,McAtee, Rory C.,Stephenson, Corey R.J.
, p. 1369 - 1373 (2018)
Alkene aminoarylation with a single, bifunctional reagent is a concise synthetic strategy.We report a catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivity to provide 2,2-diarylethylamines. In this process, single-electron alkene oxidation enables carbon-nitrogen bond formation to provide a key benzylic radical poised for a Smiles-Truce 1,5-aryl shift. This reaction is redox-neutral, exhibits broad functional group compatibility, and occurs at room temperature with loss of sulfur dioxide. As this process is driven by visible light, uses readily available starting materials, and demonstrates convergent synthesis, it is well suited for use in a variety of synthetic endeavors.
Ruthenium-catalyzed estragole isomerization: High trans-selective formation of anethole
Lastra-Barreira, Beatriz,Crochet, Pascale
, p. 1311 - 1314 (2010)
Complexes [RuCl2(η6-C6H 5OCH2CH2OH)(L)] (L = P(OMe)3 (1a), P(OEt)3 (1b), P(OiPr)3 (1c), P(OPh)3 (1d), PPh3 (1e)) have shown to be efficient catalysts for the isomerization of estragole into anethole, the best activities being obtained in polar solvents (water, methanol, ethanol). Interestingly, a complete selectivity toward trans-anethole could be reached under smooth conditions (80 °C) and in very short times (5-15 min). The catalytic experiments have been performed both under conventional and microwave heating, reaction rates being significantly enhanced under the latter conditions. The Royal Society of Chemistry 2010.
Micellar promoted alkenes isomerization in water mediated by a cationic half-sandwich Ru(II) complex
Sperni, Laura,Scarso, Alessandro,Strukul, Giorgio
, p. 535 - 539 (2017)
Micellar media in water provide a simple and efficient environment to favor the double bond isomerization of terminal alkenes catalyzed by the cationic half-sandwich complex 1 at 95 °C. The micellar medium favors both catalyst dissolution in water by means of ion-pairing with the preferred anionic surfactants as well as substrate dissolution thus favoring its conversion into products.
Singlet state Cis,Trans photoisomerization and intersystem crossing of 1-arylpropenes
Lewis, Frederick D.,Bassani, Dario M.,Caldwell, Richard A.,Unett, David J.
, p. 10477 - 10485 (1994)
The temperature dependence of the singlet state lifetime and photoisomerization and fluorescence quantum yields for trans- and cis-1-phenylpropene have been determined in hexane solution. Calculated barriers for twisting about the double bond on the singlet potential energy surface are 8.8 and 4.6 kcal/mol for the trans and cis isomer, respectively. The barrier for the trans isomer is sufficiently high to prevent isomerization on the singlet state surface at or below room temperature. However, isomerization occurs at low temperatures as a consequence of intersystem crossing to the triplet state, which undergoes barrierless isomerization. The quantum yield for intersystem crossing, as determined by time-resolved photoacoustic calorimetry, is 0.60 ± 0.03 and the rate constant for intersystem crossing is 4.7 × 107 s-1. While internal conversion is not significant at or below room temperature, thermally activated internal conversion competes with singlet isomerization at high temperatures. The cis isomer undergoes isomerization predominantly via the singlet state at room temperature. Both electron-donating (p-methoxy) and electron-withdrawing (m- and p-cyano, p-carbomethoxy, and p-trifluormethyl) aromatic substituents are found to lower the barrier for singlet state isomerization. Increased solvent polarity (acetonitrile vs hexane) results in variable decreases in the barrier for singlet state isomerization. Photoisomerization of the p-cyano derivative at room temperature occurs predominantly via the triplet state in hexane solution and via the singlet state in acetonitrile solution. The effects of substituents and solvent are better correlated with the magnitude of the S2-S1 energy gap than the stability of either zwitterionic or biradical intermediates. Rate constants for intersystem crossing are, in most cases, not highly dependent upon aromatic substitution or solvent polarity.
A Facile, Convenient, and Green Route to (E)-Propenylbenzene Flavors and Fragrances by Alkene Isomerization
Larsen, Casey R.,Paulson, Erik R.,Erdogan, Gulin,Grotjahn, Douglas B.
, p. 2462 - 2466 (2015)
(E)-Propenylbenzene flavors and fragrances can be made and isolated in high yield and selectivity by using bifunctional catalyst 1, and the heterogenized analogues. Multigram-scale reactions can be performed neat and the products isolated either by distillation, using homogeneous catalyst 1 (0.1-0.5 mol%, r.t., 10-45 min), or by decantation from heterogeneous catalysts PS-1 or PSL-1 (0.5 mol%, 70 °C, 24 h; catalyst separation and re-use shown for 3-4 cycles; 10 cycles using distilled eugenol feedstock). Both purified starting materials and essential oil feedstocks could be used. Z Isomers were present at very low levels (from 0.4% to less than 0.1%) in the products.
Synthesis, Reactivity, and Coordination of Semihomologous dppf Congeners Bearing Primary Phosphine and Primary Phosphine Oxide Groups
Horky, Filip,Císa?ová, Ivana,?těpni?ka, Petr
, p. 427 - 441 (2021/02/06)
This contribution reports the synthesis of two phosphinoferrocene ligands desymmetrized by an inserted methylene spacer, viz., a bis-phosphine combining primary and tertiary phosphine moieties in its structure, Ph2PfcCH2PH2 (2), and a structurally unique, stable phosphine-primary phosphine oxide Ph2PfcCH2P(O)H2 (7; fc = ferrocene-1,1′-diyl). Compounds 2 and 7, together with 1,1′-bis(diphenylphosphino)ferrocene (dppf), the bis-tertiary phosphine Ph2PfcCH2PPh2, and the adduct Ph2P(BH3)fcCH2PH2 (6), were studied as ligands in Ru(II) complexes bearing auxiliary ν6-arene ligands and both free ligands and the isolated complexes were structurally authenticated, using spectroscopic methods and X-ray crystallography, and further investigated by cyclic voltammetry. The results suggest that distinct donor moieties in the unsymmetric ligands differentiate the otherwise identical coordinated metal centers and that the phosphine moiety in phosphine-phosphine oxide ligand 7 is preferably coordinated to Ru(II), before the phosphine oxide group, which must tautomerize into the hydroxyphosphine form prior to coordination.
Highly Z-Selective Double Bond Transposition in Simple Alkenes and Allylarenes through a Spin-Accelerated Allyl Mechanism
Kim, Daniel,Pillon, Guy,Diprimio, Daniel J.,Holland, Patrick L.
supporting information, p. 3070 - 3074 (2021/03/08)
Double-bond transposition in alkenes (isomerization) offers opportunities for the synthesis of bioactive molecules, but requires high selectivity to avoid mixtures of products. Generation of Z-alkenes, which are present in many natural products and pharmaceuticals, is particularly challenging because it is usually less thermodynamically favorable than generation of the E isomers. We report a β-dialdiminate-supported, high-spin cobalt(I) complex that can convert terminal alkenes, including previously recalcitrant allylbenzenes, to Z-2-alkenes with unprecedentedly high regioselectivity and stereoselectivity. Deuterium labeling studies indicate that the catalyst operates through a π-allyl mechanism, which is different from the alkyl mechanism that is followed by other Z-selective catalysts. Computations indicate that the triplet cobalt(I) alkene complex undergoes a spin state change from the resting-state triplet to a singlet in the lowest-energy C-H activation transition state, which leads to the Z product. This suggests that this change in spin state enables the catalyst to differentiate the stereodefining barriers in this system, and more generally that spin-state changes may offer a route toward novel stereocontrol methods for first-row transition metals.
An Amine-Assisted Ionic Monohydride Mechanism Enables Selective Alkyne cis-Semihydrogenation with Ethanol: From Elementary Steps to Catalysis
Huang, Zhidao,Wang, Yulei,Leng, Xuebing,Huang, Zheng
supporting information, p. 4824 - 4836 (2021/04/07)
The selective synthesis of Z-alkenes in alkyne semihydrogenation relies on the reactivity difference of the catalysts toward the starting materials and the products. Here we report Z-selective semihydrogenation of alkynes with ethanol via a coordination-induced ionic monohydride mechanism. The EtOH-coordination-driven Cl- dissociation in a pincer Ir(III) hydridochloride complex (NCP)IrHCl (1) forms a cationic monohydride, [(NCP)IrH(EtOH)]+Cl-, that reacts selectively with alkynes over the corresponding Z-alkenes, thereby overcoming competing thermodynamically dominant alkene Z-E isomerization and overreduction. The challenge for establishing a catalytic cycle, however, lies in the alcoholysis step; the reaction of the alkyne insertion product (NCP)IrCl(vinyl) with EtOH does occur, but very slowly. Surprisingly, the alcoholysis does not proceed via direct protonolysis of the Ir-C(vinyl) bond. Instead, mechanistic data are consistent with an anion-involved alcoholysis pathway involving ionization of (NCP)IrCl(vinyl) via EtOH-for-Cl substitution and reversible protonation of Cl- ion with an Ir(III)-bound EtOH, followed by β-H elimination of the ethoxy ligand and C(vinyl)-H reductive elimination. The use of an amine is key to the monohydride mechanism by promoting the alcoholysis. The 1-amine-EtOH catalytic system exhibits an unprecedented level of substrate scope, generality, and compatibility, as demonstrated by Z-selective reduction of all alkyne classes, including challenging enynes and complex polyfunctionalized molecules. Comparison with a cationic monohydride complex bearing a noncoordinating BArF- ion elucidates the beneficial role of the Cl- ion in controlling the stereoselectivity, and comparison between 1-amine-EtOH and 1-NaOtBu-EtOH underscores the fact that this base variable, albeit in catalytic amounts, leads to different mechanisms and consequently different stereoselectivity.
