6937-96-8Relevant academic research and scientific papers
Monodentate Transient Directing Group Enabled Pd-Catalyzed Ortho-C-H Methoxylation and Chlorination of Benzaldehydes
Li, Feng,Zhou, Yirong,Yang, Heng,Wang, Ziqi,Yu, Qinqin,Zhang, Fang-Lin
supporting information, p. 3692 - 3695 (2019/05/24)
We report Pd-catalyzed ortho-C-H methoxylation and chlorination of benzaldehydes by employing monodentate transient directing groups (TDGs) as an alternative strategy to bidentate TDGs. More importantly, a single crystal of benzaldehyde imine ortho-cyclopalladium intermediate was successfully obtained, and its structure was unambiguously determined by X-ray diffraction, which clearly showed that it was a binuclear palladium species bridged by a pyridone ligand. The utility of this approach was further demonstrated through the synthesis of key intermediates of natural products and drugs.
Chemical reactivity and skin sensitization potential for benzaldehydes: Can Schiff base formation explain everything?
Natsch, Andreas,Gfeller, Hans,Haupt, Tina,Brunner, Gerhard
, p. 2203 - 2215 (2013/01/15)
Skin sensitizers chemically modify skin proteins rendering them immunogenic. Sensitizing chemicals have been divided into applicability domains according to their suspected reaction mechanism. The widely accepted Schiff base applicability domain covers aldehydes and ketones, and detailed structure-activity-modeling for this chemical group was presented. While Schiff base formation is the obvious reaction pathway for these chemicals, the in silico work was followed up by limited experimental work. It remains unclear whether hydrolytically labile Schiff bases can form sufficiently stable epitopes to trigger an immune response in the living organism with an excess of water being present. Here, we performed experimental studies on benzaldehydes of highly differing skin sensitization potential. Schiff base formation toward butylamine was evaluated in acetonitrile, and a detailed SAR study is presented. o-Hydroxybenzaldehydes such as salicylaldehyde and the oakmoss allergens atranol and chloratranol have a high propensity to form Schiff bases. The reactivity is highly reduced in p-hydroxy benzaldehydes such as the nonsensitizing vanillin with an intermediate reactivity for p-alkyl and p-methoxy-benzaldehydes. The work was followed up under more physiological conditions in the peptide reactivity assay with a lysine-containing heptapeptide. Under these conditions, Schiff base formation was only observable for the strong sensitizers atranol and chloratranol and for salicylaldehyde. Trapping experiments with NaBH3CN showed that Schiff base formation occurred under these conditions also for some less sensitizing aldehydes, but the reaction is not favored in the absence of in situ reduction. Surprisingly, the Schiff bases of some weaker sensitizers apparently may react further to form stable peptide adducts. These were identified as the amides between the lysine residues and the corresponding acids. Adduct formation was paralleled by oxidative deamination of the parent peptide at the lysine residue to form the peptide aldehyde. Our results explain the high sensitization potential of the oakmoss allergens by stable Schiff base formation and at the same time indicate a novel pathway for stable peptide-adduct formation and peptide modifications by aldehydes. The results thus may lead to a better understanding of the Schiff base applicability domain.
Stereoselective synthesis of 4-dehydroxydiversonol employing enantioselective palladium-catalysed domino reactions
Tietze, Lutz F.,Spiegl, Dirk A.,Stecker, Florian,Major, Julia,Raith, Christian,Grosse, Christian
experimental part, p. 8956 - 8963 (2009/10/10)
The stereoselective synthesis of 4-dehydroxydiversonol (4) employing enantioselective palladium-catalysed domino processes such as the domino Wacker-Heck and the domino Wacker-carbonylation reaction for the formation of the central chroman moiety is described. Thus, reaction of 8 with palladium(II) trifluoroacetate [Pd(OTFA)2] in the presence of carbon monoxide, methanol and the 2,2′-bis(oxazolin-2-yl)-1,1'-binaphthyl (BOXAX) ligand 17 led to 19 in 80% yield and 96% ee. Similarly, the chroman 7 was prepared using 8 and methyl acrylate (9) as starting material. Hydrogenation of the double bond, oxidation of the benzylic methylene group and intramolecular acylation of chromanone 6 provided the tetrahydroxanthenone core 5, from which the synthesis of 4 was completed. The relative configuration of 4 could be established by crystal structure analysis.
Reaction of phenols with the 2,2-diphenyl-1-picrylhydrazyl radical. Kinetics and DFT calculations applied to determine ArO-H bond dissociation enthalpies and reaction mechanism
Foti, Mario C.,Daquino, Carmelo,Mackie, Iain D.,DiLabio, Gino A.,Ingold
experimental part, p. 9270 - 9282 (2009/04/07)
(Figure Presented) The formal H-atom abstraction by the 2,2-diphenyl-1-picrylhydrazyl (dpph?) radical from 27 phenols and two unsaturated hydrocarbons has been investigated by a combination of kinetic measurements in apolar solvents and density functional theory (DFT). The computed minimum energy structure of dpph? shows that the access to its divalent N is strongly hindered by an ortho H atom on each of the phenyl rings and by the o-NO2 groups of the picryl ring. Remarkably small Arrhenius pre-exponential factors for the phenols [range (1.3-19) × 105 M-1 s-1] are attributed to steric effects. Indeed, the entropy barrier accounts for up to ca. 70% of the free-energy barrier to reaction. Nevertheless, rate differences for different phenols are largely due to differences in the activation energy, Ea,1 (range 2 to 10 kcal/mol). In phenols, electronic effects of the substituents and intramolecular H-bonds have a large influence on the activation energies and on the ArO-H BDEs. There is a linear Evans-Polanyi relationship between E a,1 and the ArO-H BDEs: Ea,1/kcal x mol-1 = 0.918 BDE(ArO-H)/kcal x mol-1 - 70.273. The proportionality constant, 0.918, is large and implies a "late" or "product-like" transition state (TS), a conclusion that is congruent with the small deuterium kinetic isotope effects (range 1.3-3.3). This Evans-Polanyi relationship, though questionable on theoretical grounds, has profitably been used to estimate several ArO-H BDEs. Experimental ArO-H BDEs are generally in good agreement with the DFT calculations. Significant deviations between experimental and DFT calculated ArO-H BDEs were found, however, when an intramolecular H-bond to the O? center was present in the phenoxyl radical, e.g., in ortho semiquinone radicals. In these cases, the coupled cluster with single and double excitations correlated wave function technique with complete basis set extrapolation gave excellent results. The TSs for the reactions of dpph ? with phenol, 3- and 4-methoxyphenol, and 1,4-cyclohexadiene were also computed. Surprisingly, these TS structures for the phenols show that the reactions cannot be described as occurring exclusively by either a HAT or a PCET mechanism, while with 1,4-cyclohexadiene the PCET character in the reaction coordinate is much better defined and shows a strong π-π stacking interaction between the incipient cyclohexadienyl radical and a phenyl ring of the dpph? radical.
Synthesis of diverse analogues of Oenostacin and their antibacterial activities
Srivastava, Vandana,Darokar, Mahendra P.,Fatima, Atiya,Kumar,Chowdhury, Chinmay,Saxena, Hari Om,Dwivedi, Gaurav R.,Shrivastava, Kunal,Gupta, Vivek,Chattopadhyay,Luqman, Suaib,Gupta,Negi, Arvind S.,Khanuja, Suman P.S.
, p. 518 - 525 (2008/03/12)
Several diverse analogues of Oenostacin, a naturally occurring potent antibacterial phenolic acid derivative, have been synthesized. A small library with more than forty analogues having different aromatic rings and varied side chains has been achieved through solution phase synthesis. Some of these analogues, that is, 22, 23 and 42, possessed potent antibacterial activities against Staphylococcus epidermidis and Staphylococcus aureus having EC50 ranging from 0.49 to 0.67 μM as compared to Oenostacin (EC50 = 0.12 μM).
The total synthesis of the fungal metabolite diversonol
Nising, Carl F.,Ohnemueller, Ulrike K.,Braese, Stefan
, p. 307 - 309 (2007/10/03)
(Chemical Equation Presented) Mission accomplished. The fungal metabolite diversonol has been synthesized for the first time. A key step in the total synthesis was the domino oxa-Michael-aldol condensation of salicylic aldehyde 1 and 4-hydroxycyclohexenon
Synthesis of chiral chromans by the Pd-catalyzed asymmetric allylic alkylation (AAA): Scope, mechanism, and applications
Trost, Barry M.,Shen, Hong C.,Dong, Li,Surivet, Jean-Philippe,Sylvain, Catherine
, p. 11966 - 11983 (2007/10/03)
The Pd-catalyzed asymmetric allylic alkylation (AAA) of phenol allyl carbonates serves as an efficient strategy to construct the allylic C-O bond allowing access to chiral chromans in up to 98% ee. The effect of pH and the influence of olefin geometry, as well as substitution pattern on the ee and the absolute configuration of the chiral chromans were explored in detail. These observations suggest a mechanism involving the cyclization of the more reactive π-allyl palladium diastereomeric intermediate as the enantiodiscriminating step (Curtin-Hammett conditions). This methodology led to the enantioselective synthesis of the vitamin E core, the first enantioselective total synthesis of (+)-clusifoliol and (-)-siccanin, and the synthesis of an advanced intermediate toward (+)-rhododaurichromanic acid A.
