24. Determining Chemical Structure by Isomer Counting (1869)
Research Topic: DiabetologySkatole or 3-methylindole is methyl pyruvate molar mass mildly toxic white crystalline organic compound belonging to the indole family. It occurs naturally in feces it is produced from tryptophan in the mammalian digestive tract and coal tar and has a strong fecal odor. In low concentrationsit methyl pyruvate molar mass a flowery smell and is found in several flowers and essential oilsincluding those of orange blossomsjasmineand Ziziphus mauritiana. It is metyyl as a fragrance and fixative in many perfumes and as an aroma compound. Its pryuvate is derived from the Greek root skato- meaning "feces".
The structurally related ester-linked model derivatives also remained unreactive upon irradiation. Preferential hydrogen-abstraction from the E-cis-substituent is suggested to explain the observed differences in cyclization ability.
Photodecarboxylative Addition of Carboxylates to Phthalimides: Oct Tetrahedron Letters. A series of 3- alkyl and aryl methyleneisoindolinone derivatives were synthesized in a simple two-step procedure using a recently established photodecarboxylative addition of carboxylates to phthalimides as the key-step.
Subsequent acid-catalyzed dehydration and deprotection furnished the desired target compounds with high E-selectivity. The reaction sequence was applied to the synthesis of the known bioactive phenylethylene derivative, AKS Different analogues, including heteroatom-containing isosteres were also synthesized using this approach.
Synthesis, structural characterization and photoisomerization of cyclic stilbenes. Six cyclic stilbene derivatives with hindered free rotation around the C vinyl —C phenyl single bond were synthesized by McMurry coupling.
The torsion angles around the double and the single bond, and the CC bond length were obtained for many of the compounds from their solid-state structures. The photochemical isomerization was subsequently investigated for all derivatives under various conditions. The parent 1- 1-tetralinylidene tetralin underwent efficient oxidative electrocyclization. Novel Building Blocks for Asymmetric Catalysis. Synthesis of Benzopyrrolizidines and Macrocyclic Lactones. Diels—Alder Oligomers of Benzene.
An Entry to trans-1,3-Disubstituted Dihydroisobenzofurans. Stereoselectivity of Triplet Photocycloadditions. Ring sizes available by this method span from 4 benzazepine-1,5-dione 7 to 26 cyclodipeptide 26e. Ground-state template formation is proposed as the explanation for the high efficiency of this reaction and for the decrease in reactivity in the presence of organic bases instead of metal carbonates. The crucial step in this macrocyclization reaction seems to be the protonation of the intermediary ketyl radiais Scheme 4.
Spacer groups investigated were alkyl chains C3-C The C,C radical combination step proceeds with low stereoselectivity cf.
Except for the lactones 22, all products were stable under the photolysis conditions. Prolonged irradiation of 22 led to the formation of the spiro compounds 23, probably via an intermediary acyliminium betaine Scheme 8. One serious limitation of the decarboxylative macrocyclization is its incompatibility with the glycine spacer as in 27a and 27b , probably the consequence of a strong intramolecular H-bond Scheme Synthesis, Structure, and Some Properties of 2,5,7,Tetraiodo-1,6- methano 10 annulene.
A New Isomer of Porphyrin. Photodecarboxylative Benzylations of Phthalimides. Octaethyltetraoxaporphyrin Dication - Counterpart of Octaethylporphyrin in the Tetraoxaporphyrin Series.
Photodecarboxylative benzylations of phthalimides. Nov Tetrahedron Letters. Irradiation of 1,4-naphthoquinone at 25 rim in benzene and in the presence of aliphatic aldehydes readily yields acylated hydroquinones in good to high yields.
The developed protocol represents a significant improvement over the original procedure using medium-pressure mercury lamps. Subsequent oxidation gives the corresponding acylated quinones. An efficient and modular approach to bidentate phosphine-phosphite ligands formally derived from a 6-alkylphosphanylphenol, a chiral diol and phosphorus trichloride has been developed. In a key step, a borane-protected phosphinite, prepared from an o-bromophenol by O-phosphanylation, is reacted with n-butyllithium to afford the corresponding ortho-phosphanylphenol as the stable borane adduct through bromine-lithium exchange and anionic migration rearrangement.
In contrast to an earlier approach, the new methodology is very general and tolerates bulky ortho-substituents. The reliability of the operationally convenient protocol was demonstrated in the synthesis of a library of 16 new phosphine-phosphite ligands, starting from different ortho-alkylphenols. The modular concept opens a rapid access to a broad variety of ligands and might be useful in the search for and structural optimization of suitable ligands for specific chirogenic transition metal-catalyzed transformations.
Exploiting the high rate of bromine-lithium exchange reactions, aryl carbinols such as fenpy-type ligands are readily obtained by simply combining a mixture of a ketone and an aryl bromide with butyllithium. Novel Spirofused Bis-Trioxane Peroxides. A set of new bis-spirofused 1,2,4-trioxanes 4a-d was obtained from the reaction of cyclohexane-1,4-dione with allylic hydroperoxides 2a-d, bearing an additional hydroxy group in the homoallylic position, by diastereoselective photooxygenation of allylic alcohols 1a-d and subsequent BF 3 -catalyzed peroxyacetalization with the diketone.
From the reaction of a monoprotected cyclohexane-1,4-dione 5 with the allylic hydroperoxide 6 derived from the singlet oxygenation of methyl hydroxytiglate, one monospiro compound was obtained, the 1,2,4-trioxane ketone 7, as well as a mixture of the diastereoisomeric syn- and anti bis-1,2,4-trioxanes 8. The structures of bis-1,2,4-trioxanes were examined theoretically by DFT methods and compared with X-ray structural data in order to evaluate the preferential trioxane ring conformational orientation.
A modular synthesis for chiral and non-symmetrical salalen ligands i. Aiming at optimal activity and enantioselectivity in the titanium-catalyzed asymmetric epoxidation of non-functionalized olefins, a positional scanning of the two ligand halves was carried out. The composition of the titanium complex catalysts was determined by high resolution mass spectrometry and X-ray crystallography for one selected example. Synthesis of a Mumbaistatin Analogue through Cross-Coupling.
Studies on the total synthesis of mumbaistatin, the strongest natural inhibitor of G6P-T1, have culminated in the synthesis of a 4",8-dideoxy analogue.
Key steps include a Diets-Alder reaction for the construction of the functionalized anthraquinone, a palladium-catalyzed Stille coupling to generate a tetra-ortho-substituted diarylmethane, and a titanium-mediated alkynylation of an aldehyde to complete the carbon skeleton of mumbaistatin.
Radical bromination of the methylene bridge afforded a lactone, which resembles the target structure in its cyclized form. Aug European Journal of Organic Chemistry. The configurational stability of reactive intermediates cation, radical and anion derived from ethylcyclobutadiene—Fe CO 3 by formal abstraction of a hydride, a hydrogen atom or a proton from the pseudobenzylic position was investigated.
Density functional calculations Becke3lyp predicted that all these reactive intermediates can be regarded as planar chiral structures having a significant configurational stability.
The racemization barriers were calculated to be In an experimental part of the study, derivatives of the 1-hydroxyethyl-substituted complex, which was enantioselectively prepared by CBS reduction of the acetyl complex, were subjected to SN1-type as well as single-electron-transfer-driven umpolung reactions.
The observed stereospecificity of these transformations retention of configuration is in accordance with the predicted configurational stability of the involved reactive intermediates. KGaA, Weinheim, Germany, The first synthetic entry towards the cyclocitrinols, a new class of natural products possessing a steroid-analogue structure with a characteristic bicyclo[4.
In the key step, a cyclopropanated intermediate prepared from dehydroepiandrosterone was subjected to reductive fragmentation using Sml 2 in THF. In the area of catalytic asymmetric epoxidation, the highly enantioselective transformation of cyclic enones and quinones is an extremely challenging target.
With the aim to develop new and highly effective phase-transfer catalysts for this purpose, we conducted a systematic structural variation of PTCs based on quinine and quinidine. In the total of 15 new quaternary ammonium PTCs, modifications included, for example, the exchange of the quinine methoxy group for a free hydroxyl or other alkoxy substituents, and the introduction of additional elements of chirality through alkylation of the alkaloid quinuclidine nitrogen atom by chiral electrophiles.
For example, the well-established 9- anthracenylmethyl group was exchanged for a "chiral" anthracene in the form of 9-chloromethyl-[ 1,8-S;4,5-R -1,2,3,4,5,6,7,8-octahydro-1,4: The asymmetric epoxidation of vitamin K 3 was used as the test reaction for our novel PTCs.
The readily available PTC 10 derived from quinine in three convenient and high-yielding steps proved to be the most enantioselective catalyst for this purpose known to date: At a catalyst loading of only 2. To rationalize the sense of induction effected by our novel phase-transfer catalysts, a computational analysis of steric interactions in the intermediate chlorooxy enolate-PTC ion pair was conducted.
Based on this analysis, the sense of induction for all 15 novel PTCs could be consistently explained. Sequential modification of the modular catalyst structure and subsequent screening of the compounds in the alcoholytic dynamic kinetic resolution DKR of azlactones revealed valuable structure-activity relationships.
In particular, a "hit-structure" was identified which provides e. Strong influence of peripheral substituents on the molecular structure. We investigated the influence of peripheral ethyl substituents on the relative stability of the Z and E isomers of octaethylisoporphycene 1a using calculations at DFT level. Compared to the parent compound isoporphycene 1 , for which the Z isomer is found to have a lower energy than the E isomer, the order of stability is reversed, if the ethyl groups are taken into consideration.
The predicted preference of the E configuration in 1a agrees with experimental observations. An analysis of the molecular geometries reveals that the different behaviour of 1 and 1a results from steric interactions between the ethyl substituents and between these substituents and H atoms of the CH 3 bridge.
For the nickel complex of isoporphycene 2 the calculated energy difference between Z and E isomer is larger and the effect of ethyl substitution is less pronounced than in the case of the free base. As a result, the Z-configured form remains the more stable isomer in the octaethyl derivative 2a.
Enantiomerically Pure Isophorone Diamine [3- Aminomethyl -3,5,5-trimethylcyclohexylamine]: Jan The Journal of Organic Chemistry. Starting from this industrial bulk product, the preparation of the bis-tosyl, bis-Fmoc, bis-Boc and bis-Z derivatives of cis-IPDA, the preparation of the pure cis enantiomers by HPLC on chiral stationary phase, and the assignment of absolute configurations to the isolated enantiomers are described.
We furthermore report an efficient method for the optical resolution of IPDA by salt formation with dibenzoyl tartaric acid. The latter method conveniently affords enantiomerically pure cis-IPDA in g quantities. A number of salen ligands have been prepared from this enantiomerically pure 1,4-diamine and fully characterized.
The nickel complex of one of the salen ligands was prepared and analyzed by X-ray crystallography. The crystal structure of the Ni4L4 complex illustrates the pronounced preference of cis-IPDA for adopting the chair conformation in which both the amino- and the aminomethyl substituents occupy equatorial positions.
As a consequence, the two salicylidene imine moieties of one ligand molecule do not converge on one metal ion, but act as bridging ligands between two nickel ions. In the title compound systematic name: In the crystal structure, pairwise C-aryl-H Parallel layers of ribbons are crosslinked by additional C-vinyl-H Ribbons of alternating R 16 and R 22 ring motifs.
Johann Lex's research works | University of Cologne, Köln (UOC) and other places
Skatole or 3-methylindole is a mildly toxic white crystalline organic compound belonging to the Melting point, 93 to 95 °C ( to °F; to K). Abstract. The kinetics of the two purified forms of pyruvate kinase from Salmonella typhimurium LT-2 were studied in assays at pH where the relationships. The enzymes pyruvate formate lyase, anaerobic ribonucleotide reductase, the of the anaerobic toluene degradation, adding the methyl group of toluene to the composing a heterohexamer (α2β2γ2) with a total molecular mass of kDa.