Volume 69, Issue 5

Graphical Abstract Chemistry of Iminium Salts, Imines, and Related Compounds

Iminium salt structures are widespread in nature and play an important role in biochemical processes. Among these thiamine diphosphate (ThPP, Vitamine B1) is one of the best known examples. It serves as a cofactor in a variety of different enzymes that are found in all forms of life. During fermentation for the production of alcoholic beverages, ThPP is of great importance not only for the key step (decarboxylation of pyruvate), but also for the formation of secondary metabolites which highly influence the aroma of wine. Thus, enzymatic degradation of amino acids in yeasts via the Ehrlich pathway delivers higher alcohols, fatty acids and esters. In malolactic fermentation, ThPPdependant enzymes (ligases) form new C-C bonds to synthezise the highly aroma-active substance diacetyl. This article summarizes the influence of ThPP on the sensorically important substances during wine making processes. Graphical Abstract Thiaminpyrophosphat – ein natürlich vorkommendes Iminium-Salz. Seine Bedeutung für die mikrobiellen Prozesse bei der Weinbereitung und die Aromabildung im Wein / Thiamine Diphosphate – A Natural Iminium Salt. Its Role in Microbiological Processes During Wine Preparation and on the Aroma of Wine

By reaction of heterocyclic-substituted 1-azo-naphth-2-ols with the Vilsmeier reagent or with strong acids polycyclic azolo[1,2,4]triazinium salts are formed in good yields. The azolo[1,2,4] triazinium salts exhibit similar UV=Vis absorption properties as the starting azo compounds, but in contrast to those the fluorescence appears in the visible range. Graphical Abstract Formation of Azolo[1,2,4]triazinium Salts by Reaction of Heterocyclicsubstituted 1-Azo-naphthalen-2-ols with Strong Acids

The preparation of new substituted methyl 3-azidothieno[2,3-b]pyridine carboxylates by azotization of methyl 3-aminothieno[2,3-b]pyridine and subsequent treatment with sodium azide is described. Via Huisgen’s 1,3-dipolar cycloaddition between substituted alkynes and the prepared azides, methyl 1,2,3-triazolo-thieno[2,3-b]pyridine carboxylates have been obtained. Graphical Abstract Synthesis of Methyl 3-Azidothieno[2,3-b]pyridine-2-carboxylates and Application of the Huisgen Reaction

1,3-Dimethylthymine can be prepared in a single-step reaction by heating a mixture of N-methylpropionamide and the Bredereck-Simchen reagent [tert-butyloxy-bis(dimethylamino) methane]. Graphical Abstract Orthoamide und Iminiumsalze, LXXXVII [1]. Eine neue, einfache Synthese für 1,3-Dimethylthymin / Orthoamides and Iminium Salts LXXXVII [1]. A New and Facile Synthesis of 1,3-Dimethylthymine

Tris(chloromethyl)amine (4) can be prepared by chloromethylation of urotropin with paraformaldehyde or 1,3,5-trioxane and ethyl-trichlorosilane in good yields. Photochlorination of tris(chloromethyl)amine affords tris(dichloromethyl)amine (2). Both reactions can be performed on large scale. Graphical Abstract Orthoamide und Iminiumsalze, LXXXIV [1]. Die Synthese von starken Formylierungsmitteln im präparativen Großmaßstab: Tris(dichlormethyl)amin / Orthoamides and Iminiumsalts LXXXIV [1]. The Synthesis of Strong Formylating Reagents on a Large Preparative Scale: Tris(chloromethyl)amine

N;N;N';N'-Tetraformylhydrazine (3) can be pepared in good yields by heating of N;N'-diformylhydrazine (5) with N;N-diformylacetamide (6). The reaction of methanesulfonyl chloride with sodium diformamide (10) in a molar ratio of 2 : 5 in acetonitrile affords tris(diformylamino)methane (formyl-aalen, 2). Both reactions were used to prepare 3 and 2 in large quantities (ca. 200 to 400 g). A mechanism is proposed for the formation of 2 from methanesulfonyl chloride and 10. Graphical Abstract Orthoamide und Iminiumsalze, LXXXV [1]. Die Synthese von starken Formylierungsmitteln im präparativen Großmaßstab: N,N,N',N'- Tetraformylhydrazin und Formyl-aalen [Tris(diformylamino)methan] / Orthoamides and Iminium Salts LXXXV [1]. The Synthesis of Strong Formylating Reagents on a Large Preparative Scale: N;N;N';N'-Tetraformylhydrazine and Formyl-aalen [Tris(diformylamino)methane]

A phenothiazinyl donor moiety can be covalently coupled to aromatic hydrocarbon acceptor units via Ugi four-component reaction in an efficient, rapid, and highly convergent fashion. These novel phenothiazine-acceptor dyads are electronically decoupled in the electronic ground state according to UV/Vis spectroscopy and cyclic voltammetry. In the excited state the inherent acceptor luminescence is substantially quenched. Calculations of the Gibbs energy of photo-induced electron transfer from readily available UV/Vis spectroscopic and cyclovoltammetric data according to the Weller approximation rationalizes the feasibility of the reductive electron transfer from phenothiazine to the aromatic hydrocarbon upon photoexcitation. Graphical Abstract Phenothiazine-Aromatic Hydrocarbon Acceptor Dyads as Photo-induced Electron Transfer Systems by Ugi Four-Component Reaction

Herein a simple one-pot metal-free synthesis of 2,4,5-trisubstituted pyridines and pyridine Noxides by [2+2] cycloaddition of enaminones, which are prepared in situ from alkyl, aryl and heteroaryl methyl ketones using N,N-dimethylformamide dimethyl acetal (DMFDMA), and propyne iminium salts as electron-poor acetylenes, is described. Graphical Abstract A Simple Metal-free Synthesis of 2,4,5-Trisubstituted Pyridines and Pyridine N-Oxides by [2+2] Cycloaddition of Enaminones to Propyne Iminium Salts

The reaction of equimolar amounts of propyne iminium trifluoromethanesulfonates 1a, b and isoquinoline yielded, after hydrolytic work-up, the N-(3-oxoprop-1-en-1-yl)isoquinolinium salts 4a, b in modest yields. Monitoring of the reaction by 1 H NMR spectroscopy indicated the formation of salts 4, 3-isoquinolinio-substituted propene iminium salts 3, and N,N,N',N'-tetramethylvinamidinium salts 5 as the major components. The expected aminoallenes (2-(3-(dimethylamino)allen-1- yl)isoquinolinium triflates) 2 could not be detected in the reaction solutions. It is possible, however, to trap the aminoallene intermediates in a polar [4+2] cycloaddition reaction, as shown by the isolation of 2 : 1 adducts 7c, d in good yield from cyclopropyl-substituted propyne iminium triflates 1c, d and isoquinoline. Hydride abstraction from 7c, d yielded the 2,4-dicyclopropyl-1,3- bis((dimethyliminio)(aryl)methyl)pyrido[2,1-a]isoquinolinium tris(triflates) 8c, d. Graphical Abstract Propyne Iminium Salts and Isoquinoline – 1 : 1 and 2 : 1 Adducts

Upon reaction of the dipyrido-anellated guanidinium salt 1 with one equivalent of CpNa we were able to synthesize the dipyrido-anellated diaminofulvalene 4 in one step in 33% isolated yield. This shortens the initial route that applies a literature-known fulvalene synthesis via uronium salt 3 by two steps and avoids the need for a sacrificial equivalent of CpNa. Although the X-ray structure analysis reveals a shorter exocyclic double bond than observed in the diaminofulvalene V, a theoretical analysis based upon DFT calculations shows a stronger zwitterionic character for the dipyridofulvalene 4. Graphical Abstract A Direct Synthesis of a Strongly Zwitterionic 6,6'-Diaminofulvalene

We synthesized and structurally characterized two new copper(II) monochelate complexes with the ligand 2,2'-(1,2-phenylenebis(1,1,3,3-tetramethyl)guanidine) (TMG 2 b), [Cu(TMG 2 b)Cl 2 ] and [Cu(TMG 2 b)Br 2 ]. Single-crystal structure determination has shown that the complexes [Cu(TMG 2 b)Cl 2 ] and [Cu(TMG 2 b)Br 2 ] both crystallize in the orthorhombic space group Pbcn. The copper atoms in all complex cations reside in a coordination environment between tetrahedral and square-planar geometry. Furthermore, the application of the copper complexes with TMG 2 b as ligand in atom transfer radical polymerization (ATRP) was investigated with styrene as monomer. This study has shown a controlled polymerization process with moderate conversions, but excellent molecular weight distributions that are evidence of a well-controlled ATRP. However, small changes in the ligand structure can have a high impact, and therefore process optimizations and ligand tuning are necessary to develop highly active catalysts for ATRP. Graphical Abstract Neue aromatische Bisguanidin-Kupfer-Komplexe und ihre Anwendung in der ATRP / New Aromatic Bisguanidine Copper Complexes and Their Application in ATRP

Two imidazol(in)ium-dithiocarboxylates have been investigated as sensors for the detection of mercury ions and silver ions. They could be applied as colorimetric chemosensors for the detection of Hg 2+ and Ag + . Furthermore, an additional sensory input was found by a colorimetric change of a two-phase system from the organic phase into the aqueous phase. Due to different colors at different ratios of the betaines and Hg 2+ it is possible to estimate the concentration of Hg 2+ with the ”naked eye”. Graphical Abstract Investigation of Imidazol(in)ium-dithiocarboxylates as Sensors for the Detection of Mercury(II) and Silver(I) Ions

3-Methylindole reacts with pyridines in the presence of NBS to give indol-2-yl-pyridinium salts which were converted into their ylides by an anion exchange resin in its hydroxide form. Indol-3- amine was subjected to a nucleophilic ring transformation with pyrylium salts which resulted in the formation of indol-3-yl-pyridinium salts, the 2,4,6-trimethylpyridinium derivative of which proved to be unstable. The 2,4,6-triphenylpyridinium derivate was deprotonated to the corresponding ylide. The isomeric indol-2-yl and indol-3-yl derivatives are cycloimmonium ylides which are members of the compound class of heterocyclic mesomeric betaines (MB). By contrast, the ylide of indol- 2-yl-pyrrolidinium is a cycloammonium ylide. It was prepared by reaction of 3-methylindole with pyrrolidine in the presence of NBS, followed by deprotonation. Graphical Abstract Syntheses and Characterization of N-(Indolyl)pyridinium Salts and of Their Ylides

Parallel screening of suitable reaction conditions for Cu(I)-catalyzed [3+2] cycloadditions of (1Z,4R*,5R*)-4-benzoylamino-1-benzylidene-5-phenyl-3-oxopyrazolidin-1-ium-2-ide (1a) to methyl propiolate (2) has established that this reaction proceeds smoothly at room temperature in acetonitrile in the presence of CuI and Hünig’s base. The optimized reaction conditions were then applied in regio- and stereo-selective 1,3-dipolar cycloadditions of racemic azomethine imines 1a-e to tert-butyl (S)-(3-oxopent-4-yn-2-yl)carbamate (6) leading to mixtures of diastereomeric non-racemic chromatographically separable cycloadducts 7a-d, 7'a-d, 8e, and 8'e. The structures of the products were confirmed by NMR spectroscopy. Graphical Abstract Cu(I)-catalyzed [3+2] Cycloadditions of tert-Butyl (S)-(3-Oxopent-4- yn-2-yl)carbamate to 1-Benzylidenepyrazole-3-one-derived Azomethine Imines

Synthetic approaches to novel isomers and unprecedented structural relatives of the lamellarin alkaloids are reported. During our studies on methods to construct the lamellarin skeleton, we found the condensation of chroman-4-one derivatives with 1-benzyl-3,4-dihydroisoquinolines or the Pdcatalyzed cyclocarbonylation of o-halogenated precursors followed by Baeyer-Villiger oxidation to be unsuitable. Nevertheless, these routes produced interesting structural relatives of the natural alkaloids. Graphical Abstract Zugänge zu Isomeren und Verwandten der Lamellarin-Alkaloide / Approach to Isomers and Structural Relatives of the Lamellarin Alkaloids

The cycloacylation of oxalic amidines 7 with bis-imidoylchlorides 6 furnished the dihydropyrazine derivatives 8. Due to their vicinal amino-imino substructures, they provide good preconditions for a double intramolecular ring closure reaction. An alternative synthesis for hexaaza-pentacenes 1 was developed using potassium carbonate as the base and lead tetraacetate as the oxidizing agent. Graphical Abstract Novel Dihydropyrazines and their Double ortho-Annulation to Hexaazapentacenes