Chemie freier,cyclischer vicinaler Tricarbonyl‐Verbindungen (`1,2,3‐Trione'), Teil 1, Reaktionsweise von Diazomethan und seinen Derivaten mit 5,5‐Dimethylcyclohexan‐1,2,3‐trion (=`Oxo‐dimedon') und verwandten Cyclohexan‐1,2,3‐trionen

Chemistry of Free Cyclic Vicinal Tricarbonyl Compounds (`1,2,3‐Triones'). Part 1. Reaction of Diazomethane and Its Derivatives with 5,5‐Dimethylcyclohexane‐1,2,3‐trione (=`Oxo‐dimedone') and Related Cyclohexane‐1,2,3‐triones Interactions of diazomethane and of its derivatives as typical nucleophiles with cyclic 1,2,3‐triones as efficient electrophiles lead to different results: a) formation of oxiranes (C,O insertion under loss of N₂), b) nucleophilic addition yielding diazoaldols, c) formation of ring‐enlargement products (C,C insertion under loss of N₂), and d) formation of dioxoles via redox reactions (under loss of N₂). Our results and those of other groups allow us to recognize that the unexpected outcome of the reaction of oxodimedone and several related species is due to a closed‐shell diazoaldol formation followed by an open‐shell redox reaction leading to dioxoles.     

Chemie freier cyclischer vicinaler Tricarbonyl‐Verbindungen (‘1,2,3‐Trione') Teil 2. Redox‐Reaktionen von 1,2,3‐Trionen mit En‐1,2‐diolen (‘Reduktonen'), 2‐Alkoxy‐en‐1‐olen,En‐1,2‐diaminen und verwandten Spezies

Chemistry of Free Cyclic Vicinal Tricarbonyl Compounds (‘1,2,3‐Triones'). Part 2. Redox Reactions of 1,2,3‐Triones with Ene‐1,2‐diols (‘Reductones'), 2‐Alkoxy‐en‐1‐ols, Ene‐1,2‐diamines, and Related Species . Midstanding carbonyl groups of cyclic 1,2,3‐triones 4 possess outstanding electrophilic (electron‐pair accepting) as well as oxidizing (one‐electron accepting) properties. Their reactions with selected electron‐rich CC bonds as efficient nucleophiles (A_N reactions) and as efficient reducing agents (SET (single electron transfer) reactions) are studied. In a few cases, short‐lived charge‐transfer colors could be observed. Particularly, free didehydro‐5,6‐O‐isopropyliden‐L ‐ascorbic acid ( 4g ), its O,C‐adduct 8g to 5,6‐O‐isopropylidene‐L ‐ascorbic acid ( 1g ), and – via an independent pathway – the ostensible C,C‐dimer 10a of mono‐dehydrodimedone reductone were prepared. Intermediate radical anions 4 ^.− can be considered to be ideal representatives of dicapto‐dative radicals. Novel large‐scale syntheses of 3,4‐dihydroxyfuran‐2(5H)‐one ( 1e ) and of its vicinal trione 4e are presented.     

Synthese von enantiomerenreinen ‘Grasshopper’-Ketonen und verwandten Verbindungen

Synthesis of Optically Pure Grasshopper Ketone and of Its Diastereoisomers and Related Compounds Starting from our previously described synthon 1 , the synthesis of four enantiomerically pure grasshopper ketons (diastereoisomeric 4-(2′,4′-dihydroxy-2′,6′,6′-trimethylcyclohexylidene)but-3-en-2-ons) and of their oxo derivatives was performed. Spectral and chiroptical data are presented.     

A Novel ‘Domino‐Click Approach’ to Unsymmetrical Bis‐1H‐1,2,3‐triazoles

Aryl azides 1 were treated with allenylmagnesium bromide ( 2 ) to generate 1,5‐disubstituted butynyl‐1H‐1,2,3‐triazoles 3 in a domino fashion, which upon Cu^I‐catalyzed 1,3‐dipolar cycloaddition with aryl azides 4 afforded novel bis‐1H‐1,2,3‐triazoles 5 in quantitative yields (Scheme 1 and Table).     

Nucleic-Acid Analogues with Constraint Conformational Flexibility in the Sugar-Phosphate Backbone (‘Bicyclo-DNA’). Part 1. Preparation of (3S,5′R)-2′-Deoxy-3′,5′-ethano-αβ-D-ribonucleosides (‘Bicyclonucleosides’)

We describe the synthesis of 2′-deoxy-3′,5′-ethano-D -ribonucleosides 1 – 8 (= (5′,8′-dihydroxy-2′-oxabicyclo-[3.3.0]oct-3′-yl)purines or -pyrimidines) of the nucleobases adenine, thymine, cytosine, and guanine. They differ from natural 2′-deoxyribonucleosides only by an additional ethylene bridge between the centers C(3′) and C(5′). The configuration at these centers (3S,5′R) was chosen as to match the geometry of a repeating nucleoside unit in duplex DNA as close as possible. These nucleosides were designed to confer, as constituents of an oligonucleotide chain, a higher degree of preorganization of a single strand for duplex formation with respect to natural DNA, thus leading to an entropic advantage for the pairing process. The synthesis of these ‘bicyclonucleosides’ was achieved by construction of an enantiomerically pure carbohydrate precursor 18 / 19 (Schemes 1), which was then converted to the corresponding nucleosides by known methods in nucleoside synthesis (Schemes 2 and 3). In all cases, both anomeric forms of the nucleosides were obtained in pure crystalline form, the relative configuration of which was established by ¹H-NMR-NOE spectroscopy. A conformational analysis of the nucleosides with β-configuration at the anomeric center by means of X-ray and ¹H-NMR (including NOE) spectroscopy show the furanose part of the molecules to adopt uniformly a 1′exo-conformation with the base substituents preferentially in the anti-range in the pyrimidine nucleosides (anti/syn ca. 2:1) distribution in the purine nucleosides (in solution).     

‘Click Synthesis’ of Some Novel O‐Substituted Oximes Containing 1,2,3‐Triazole‐1,4‐diyl Residues as New Analogs of β‐Adrenoceptor Antagonists

The ‘click synthesis’ of some novel O‐substituted oximes, 7a – 7t , which contain 1,2,3‐triazolediyl residues, as new analogs of β‐adrenoceptor antagonists is described (Schemes 1–4). The synthesis of these compounds was achieved in four to five steps. The formation of oximes of 9H‐fluoren‐9‐one and benzophenone, i.e., 9a and 9b , respectively, followed by their reaction with propargyl bromide, afforded O‐propargyl oximes 10a and 10b , respectively, which by a subsequent CuI‐catalyzed Huisgen cycloaddition with prepared β‐azido alcohols 11a – 11j (Schemes 2 and 3), led to the target compounds 7a – 7t in good yields.     

Copper‐supported β‐cyclodextrin‐functionalized magnetic nanoparticles: Efficient multifunctional catalyst for one‐pot ‘green’ synthesis of 1,2,3‐triazolylquinazolinone derivatives

The green synthesis of 2‐(4‐((1‐phenyl‐1H‐1,2,3‐triazol‐4‐yl)oxy)phenyl)quinazolin‐4(3H)‐one derivatives is reported. The catalyst for this synthesis is copper‐supported β‐cyclodextrin‐functionalized magnetic silica–iron oxide nanoparticles ([Cu@BCD@SiO₂@SPION]). [Cu@BCD@SiO₂@SPION] simultaneously catalyses ‘click’ reaction, oxidation of C? N bond and multicomponent reaction. The desired 1,2,3‐triazolylquinazolinone product is easily obtained in water at room temperature under mild reaction conditions. Another advantage of the catalyst is its reusability. It can simply be isolated using an external magnet and reused in reactions with no significant decrease in catalyst efficiency. Transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometry and Fourier transform infrared spectroscopy are used for exact characterization of the [Cu@BCD@SiO₂@SPION] catalyst.     

Tautomerism in 5,8‐Diaza‐7,9‐dicarbaguanine (‘Alloguanine’)

An X‐ray structure analysis of the title compound reveals that this purinoid exists in the crystal as two tautomers which interact with each other in the mode of a reverse‐Watson–Crick base pair.     

Stereoselective Synthesis of 1,2,3‐Triazolooxazine and Fused 1,2,3‐Triazolo‐δ‐Lactone Derivatives

The stereoselective synthesis of 1,2,3‐triazolooxazine and fused 1,2,3‐triazolo‐δ‐lactone by applying chemoenzymatic methods is described. trans‐2‐Azidocyclohexanol was successfully resolved by Novozyme 435 with an ee value of 99%. Installation of the alkyne moiety on the enantiomerically enriched azidoalcohol by O‐alkylation, followed by intramolecular azide? alkyne [3+2] cycloaddition resulted in the desired 1,2,3‐triazolooxazine derivative. Enantiomerically pure azidocyclohexanol was also subjected to the Huisgen 1,3‐dipolar cycloaddition reaction with dimethylacetylene dicarboxylate, followed by intramolecular cyclization of the corresponding cycloadduct, to furnish a fused 1,2,3‐triazolo‐δ‐lactone.     

Synthesis of (S)‐3‐heteroaryl‐2‐hydroxy‐l‐propyl benzoates by ‘ring switching’ methodology

(S)‐5‐Benzoyloxymethyl‐3‐[(E)‐(dimethylamino)methylidene]tetrahydrofuran‐2‐one (6), prepared in 5 steps from L‐glutamic acid (1), was used as precursor in a one step ‘ring switching’ synthesis of (S)‐2‐hydroxy‐3‐heteroaryl‐l‐propyl benzoates 13‐18, 23, 24. In the reaction of 6 with 2‐aminopyridine (21) and 2‐amino‐4,6‐dimethylpyrimidine (22) the corresponding dimethylamine substitution products (25, 26) were obtained.     

Two 1,3‐Diazabicyclo[3.1.0]hex‐3‐enes with a ‘Tripod’ Core

The photochromic 1,3‐diazabiclyclo[3.1.0]hex‐3‐enes 5 and 6 were synthesized from two premade tris‐aldehydes and two premade aziridinyl ketones and characterized (Scheme 1). Their spectra showed structure? photochromic behavior relationships (SPBR), which were analyzed.     

Synthese von ‘D-Isothreonin’ und ‘L-Alloisothreonin’ aus L-Alanin

Synthesis of ‘D -Isothreonine’ and ‘L -Alloisothreonine’ Starting from L -Alanine Starting from L -alanine, ‘D -isothreonine’ ( = (2R, 3S)-3-amino-2-hydroxybutanoic acid) and ‘L -alloisothreonine’ ( = (2S, 3S)-3-amino-2-hydroxybutanoic acid) were synthesized.     

1,2,3-三氮杂苯－(水)3复合物多体相互作用

The interaction between 1,2,3-triazine and three water molecules was studied using density functional theory B3LYP method at 6-31-t＋＋G^＊＊ basis set. Various structures for 1,2,3-triazine-（water）n （n= 1, 2, 3） complex were investigated and the different lower energy structures were reported. Many-body analysis was also carded out to obtain relaxation energy and many-body interaction energy （two, three, and four-body）, and the most stable conformer has the basis set superposition error corrected interaction energy of -- 102.61 kJ/mol. The relaxation energy, two- and three-body interactions have significant contribution to the total interaction energy whereas four-body interaction was very small for 1,2,3-triazine-（water）3 complex.     

The 5‐Methylisocytosine β‐D‐Ribopyranosyl (4′ → 2′)‐Oligonucleotide

In the context of Eschenmoser's work on pyranosyl‐RNA (‘p‐RNA’), we investigated the synthesis and base‐pairing properties of the 5‐methylisocytidine derivative. The previously determined clear‐cut restrictions of base‐pairing modes of p‐RNA had led to the expectation that a 5‐methylisocytosine β‐D ‐ribopyranosyl (= D ‐pr(^MeisoC)) based (4′ → 2′)‐oligonucleotide would pair inter alia with D ‐pr(isoG) and L ‐pr(G) based oligonucleotides (D ‐pr and L ‐pr = pyranose form of D ‐ and L ‐ribose, resp.). Remarkably, we could not observe pairing with the D ‐pr(isoG) oligonucleotide but only with the L ‐pr(G) oligonucleotide. Our interpretation concludes that this – at first hand surprising – observation is caused by a change in the nucleosidic torsion angle specific for isoC.     

The Photoelectron Spectrum of Triisopropylidenecyclopropane (‘hexamethyl-3-radialene’)

The photoelectron spectrum of the title compound 2 is discussed and compared with the results of MO-calculations for the parent unsubstituted hydrocarbon 1 . The ground-state of 2⁺ is ²E″ which is Jahn-Teller (JT) active. Assuming the e′ C=C-stretch to be responsible for breaking its degeneracy, satisfactory agreement between experimental and theoretical band shape is obtained. The latter is calculated from the diabatic two-state approximation using MINDO/3-SCF results for the JT-stabilization energies. Comparison with Rydberg studies on 1, performed by other authors, yields further evidence for the A₂″ – (not E′ –) symmetry of the Rydberg states. The next two observed higher lying states of 2⁺ are ²E′ and ²A₂″, the former also being JT-active. Theoretical calculations of the corresponding band shape point toward the e′-ring stretching mode causing instability, an outcome reminiscent of the ²E′-groundstate of cyclopropane-ion. The energetic difference between the latter state and the ²E′-state of 2⁺ is discussed using a simple MO-model with methylidene and ethylidene carbene as interacting units. The results suggest that the unsaturated carbene is strongly stabilized by hyperconjugation. The chemistry of the two carbenes is compared on this basis.