bluuebunny/crossref_metadata_2025_split huggingface dataset:
Steroidal cyclobutanones, V. the baeyer‐villiger rearrangement of α‐substituted β‐spirocyclobutanones
Authors: Paryzek Zdzislaw , Blaszczyk Krzysztof 
Published: July 2007

AbstractThe reaction of the steroidal spiro‐α,α‐dichlorocyclobutanone 1 carried out in basic H2O2/MeOH/THF solution proceeds with cine substitution leading to the intermediate α‐chloro‐α‐methoxycyclobutanone 7 followed by the Baeyer‐Villiger rearrangement giving the spiro‐α‐chloro‐γ‐methoxylactone 9 as a mixture of four stereoisomers. The oxidation of the α‐chlorocyclobutanone 12 gives the methoxylactone 10 resulting also from a cine substitution preceding the rearrangement. The unusual transformation of 1 to the succinic anhydride derivative 14 is also observed.
Regioselectivities in the catalyzed conjugate addition of organoaluminium and organotitanium reagents to sterically hindered enones: Investigation of the methylation of 10β‐methyl‐Δ1,9‐2‐octalones
Authors: Kabbara Jazid , Flemming Steffen , Nickisch Klaus , Neh Harribert , Westermann Jürgen 
Published: July 2007

AbstractRegioselectivities in Michael‐type reactions of organoaluminium and organotitanium reagents with sterically hindered carbonyl compounds 1 and 5 concerning 1,2‐ versus 1,4‐addition were determined. Throughout this investigation Me3Al/cat. Ni(acac)2 was found to be the most useful reagent for strongly hindered systems.
Planar chiral systems, IV. An efficient route for the preparation of 5‐formyl‐4‐hydroxy[2.2]paracyclophane (FHPC)
Authors: Hopf Henning , Barrett David G. 
Published: July 2007

AbstractFor the preparation of the title compound, 4‐hydroxy[2.2]paracyclophane (1) is first converted to the carbamate 2. Metalation of 2 with sec‐butyllithium yields an ortho‐anion which after trapping with dimethylformamide and acidic work‐up provides 6 in 64% yield. Further application of the cyclophane anion include its capture by trimethylsilyl chloride to the trimethylsilyl derivative 3 (76%) and its Fries rearrangement to the phenol 4 (78%). The spectroscopic and analytical data of the new compounds are described in full detail.
Studien zur Chemie von thienoanellierten O,N‐ und S,N‐haltigen Heterocyclen, 8. Synthese eines racemischen, thienoanalogen Diltiazems mit potentieller Calciumkanal blockierender Wirkung
Authors: Laimer Ingrid , Erker Thomas 
Published: July 2007

Studies on the Chemistry of Thieno‐Annulated O,N‐ and S,N‐Containing Heterocycles, 8[1].–Synthesis of a Racemic, Thieno Analogue Diltiazem with Potential Ca2+Antagonistic ActivityThe synthesis of the thieno analogue diltiazem cis‐8‐[2‐(di‐methylamino)ethyl]‐5,6,7,8‐tetrahydro‐5‐(4‐methoxyphenyl)‐7‐oxothieno[3,2‐b][1,4]thiazepin‐6‐yl acetate (1) is described. Reaction of 3‐bromo‐2‐nitrothiophene with Na2S · 9H2O yields the intermediate 3‐mercapto‐2‐nitrothiophene (6), which reacts with the racemic glycidate 7 to give the racemic threo compound 10. Reduction and cyclization of 10 furnish the thieno [3,2‐b][1,4]thiazepine derivative 12. N‐Alkylation and acetylation of the hydroxy group of 12 leads to 1.
Triazolines, 35. 2‐aminoaziridines: Unstable intermediates in thermal decomposition of 5‐amino‐v‐triazolines
Authors: Pocar Donato , Roversi Elena , Trimarco Pasqualina , Valgattarri Guido 
Published: July 2007

AbstractPyrolysis of 4‐aryl‐5‐amino‐v‐triazolines 4 affords two products: benzanilides 5 and acetamidines 6. Pyrolysis of 4 with DMAD under argon produces 1‐aza‐1,3‐dienes 8 and 2‐pyrrolines 9. The reaction mechanism of this transformation is discussed. 2‐Aminoaziridines are shown to be key intermediates in this reaction.
Cyclophanes, XXXIX. The Structure of the Dicyanoacetylene Adducts of [2.2]Paracyclophane
Authors: Hopf Henning , Witulski Bernhard , Jones Peter G. , Schomburg Dietmar 
Published: July 2007

AbstractThe structures of the 1:1 and 1:2 addition products of dicyanoacetylene (2) to [2.2]paracyclophane (1) have been determined by X‐ray structural analysis as 3 and 5, respectively. In contrast to literature reports, the latter possesses the „crossed”︁ double barrelene configuration. On irradiation 3 isomerizes to the semibullvalenophane 4 as was also shown by X‐ray structural analysis.
Rearrangement and cycloreversion of Diels‐Alder adducts of cyclic 1,3‐dienes to norbornadienes. A novel homo‐cope rearrangement. Evidence for competitive pericyclic and diradical processes
Authors: Hochstrate Dirk , Klärner Frank‐Gerrit 
Published: July 2007

AbstractOn thermolysis of endo,endo‐5, endo,endo‐17, and endo,exo‐17 (the endo,endo and endo,exo Diels‐Alder adducts of cyclopentadiene 7 or dimethylfulvene 15 to norbornadiene 8 or 7‐isopropylidenenorbornadiene 20), a novel type of homo‐Cope rearrangement leading to 6, 21, and 23a, respectively, competes with the retro‐Diels‐Alder reactions. According to a force‐field analysis of the kinetic parameters, the competitive reactions (rearrangement and retro‐Diels‐Alder reaction) of endo,endo‐5 occur in a pericyclic fashion whereas in the isopropylidene‐substituted systems stepwise processes compete with the corresponding pericyclic reactions. Indirect experimental evidence for this assumption comes from a stereochemical analysis of the refro‐Diels‐Alder reaction in the cis‐5,6‐dideuterionorbornene derivatives exo‐36‐d2, endo‐36‐d2 and exo‐39‐d2, endo‐39‐d2 occurring stereospecifically in the case of exo‐36‐d2, endo‐36‐d2 and non‐stereospecifically in the case of exo‐39‐d2, endo‐39‐d2. The change in mechanism is rationalized by a different (allyl vs. pentadienyl) stabilization of the potential diradical intermediates in the stepwise reactions.
Cinnolines and pyrazolopyridazines. — Novel synthetic and mechanistic aspects of the Richter reaction
Authors: Vasilevsky Sergei F. , Tretyakov Eugene V. 
Published: July 2007

AbstractThe thermal cyclization of 2‐alkynylbenzenediazonium salts 2 known as the Richter reaction and leading, as described in the literature, only to 4‐hydroxycinnolines 6 has been studied. A new probable route to these compounds involving intermediate formation of the 4‐chlorocinnolines 4 followed by hydrolysis of the latter to 6 is discussed. A new understanding of the reaction mechanism has induced us to change the reaction conditions in order to synthesize some 4‐bromo‐ (5), 4‐chloro‐ (4), and 4‐hydroxycinnolines 6 as well as 4‐bromo‐(8b) and 4‐chloropyrazolopyridazine 8a.
Reactions of 1,3,5‐Tri‐tert‐butylcyclopentadiene formation of a tetracyclo[5.2.1.02,6.03,10]deca‐4,8‐diene
Authors: Dehmlow Eckehard V. , Bollmann Christof 
Published: July 2007

AbstractTitle compound 1 is sterically shielded to such an extent that many „normal”︁ reactions cannot occur. It is possible, however, to prepare the carboxylic acid 2, its acyl chloride 3 and the oxidation product 4. Furthermore, halogen substitutions to yield 5 and 6 and trialkylstannations to give 8a, b can be performed. Oxidative dimerization of 1 leads to 7, and this can be rearranged to the totally unexpected tetracyclic compound 9.
Antibiotics from gliding bacteria, LXIV. Isolation and structure elucidation of sorangiolides A and B, novel macrocyclic lactone carboxylic acids from Sorangium cellulosum
Authors: Jansen Rolf , Irschik Herbert , Meyer Holger , Reichenbach Hans , Wray Victor , Schomburg Dietmar , Höfle Gerhard 
Published: July 2007

AbstractTwo novel metabolites, sorangiolide A (1) and B (2), were isolated from the mother liquors and side fractions of the sorangicin A pilot‐scale production. Their structures were elucidated by 2D‐NMR spectroscopy and mass spectrometry as 18‐membered macrolactones with a C11‐carboxylic acid side chain. Sorangiolide B (2) differs from A (1) by an additional hydroxyl group at C‐6 in the side chain. The absolute configuration of sorangiolide A (1) was established by X‐ray structure analysis. The sorangiolides show a weak antibiotic activity against Gram‐positive bacteria.
Enzymes in organic synthesis, 23. Chemo‐enzymatic synthesis of (5R,6S)‐6‐acetoxyhexadecan‐5‐olide — the major component of the mosquito oviposition attractant pheromone
Authors: Henkel Birgitta , Kunath Annamarie , Schick Hans 
Published: July 2007

AbstractThe methyl ester rac‐4a of (5R*,6S*)‐5,6‐dihydroxyhexadecanoic acid was prepared by a Wittig reaction of (4‐carboxybutyl)triphenylphosphonium bromide (2) with undecanal (1) followed by esterification with methanol and cis dihydroxylation with osmium (VIII) oxide/N‐methylmorpholine N‐oxide. After conversion of the dihydroxy ester rac‐4a into (5R*,6S*)‐6‐hydroxyhexadecan‐5‐olide (rac‐5) by lactonization (5R,6S)‐6‐acetoxyhexadecan‐5‐olide (6), the mosquito oviposition attractant pheromone, was obtained by an enantioselective lipase‐catalyzed acetylation with vinyl acetate. In an alternative route the dihydroxy ester rac‐4a was subjected to a lipase‐catalyzed lactonization, which afforded as the main product (5S,6R)‐6‐hydroxyhexadecan‐5‐olide (ent‐5), the enantiomer of the deacetylated pheromone.
Studies on electron transfer as mechanistic concept for [4 + 2] cycloadditions, 1. Cycloadditions of 1,4‐bis(dimethylamino)‐1,3‐butadiene to electron‐deficient olefins
Authors: Lücking Karin , Rese Michael , Sustmann Reiner 
Published: July 2007

Abstract(E,E)‐1 and (E,Z)‐1,4‐bis(dimethylamino)‐1,3‐butadiene (2) as model systems for highly electron‐rich dienes were allowed to react with olefins of increasing electron‐acceptor capacity under standard concentrations (0.4 M solutions of diene and dienophile) and at reaction temperatures from −50°C to a maximum of +60°C (slow decomposition of the diene). Methyl acrylate (3), acrylonitrile (4), and dimethyl methylfumarate (6) did not form cycloadducts with 1 at 35°C in six weeks. Isopropylidenemalononitrile (5) undergoes dimerization. Maleo‐ (9) and fumaronitrile (10) add to 1 with retention of stereochemistry ( ≥98%). Dimethyl maleate (7) isomerizes under the reaction conditions to dimethyl fumarate (8) and reacts with 1 to the cycloadduct of 8. N‐Methylmaleimide (11) gave the expected cycloadduct. The monosubstituted C atoms of the CC double bond of 1,1,2‐tris(methoxycarbonyl)ethene (12) and 2‐cyano‐1,1‐bis(methoxycarbonyl)‐ethene (13) add to C‐2 of 1 to form zwitterions which stabilize themselves by a 1,3‐hydrogen shift to 24 and 25. The reactions of 1 with 1,1‐dicyano‐2‐methoxycarbonylethene (14), 1,1‐dicyano‐2,2‐bis(methoxycarbonyl)ethene (15), and tetracyanoethene (18) provided, though very reactive, no isolable cycloadducts or other identifiable products. Dimethyl dicyanomaleate (16) and dimethyl dicyanofumarate (17) lead in non‐stereospecific reactions with 1 to the same cycloadduct even at −50°C in dichloromethane. The same cycloadduct is obtained from 2 and 17. For the reactions of 16 and 17 with 1 electron transfer from diene to dienophile could be demonstrated. Intermediates were detected 1H‐NMR‐spectroscopically at −95°C which transformed into the cycloadduct when warmed to−50°C. A comparison of the preparative results with oxidation potentials of 1 and 2, and the reduction potentials of the olefins shows, that electron transfer is possible when oxidation and reduction potential are close together. It is concluded from the loss of stereochemistry during the cycloadduct formation in those cases (16 and 17) where electron transfer is observed, and furthermore from retention of stereochemistry (9 and 10) when no electron transfer could be detected, that electron transfer may be a possibility in [4 + 2] cycloadditions, but that it is not the general mechanism of the Diels‐Alder reaction.
Optimised preparation of 1,5‐dialkylsemibullvalenes
Authors: Quast Helmut , Dietz Thomas , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg 
Published: July 2007

AbstractAskani's synthesis of the 1,5‐dialkylsemibullvalenes 1a and c was optimised on a gram scale. The as yet unknown trimethylenesemibullvalene 1b was obtained according to the same protocol which also greatly improved a recent synthesis of barbaralane (2). Allylic brominations of the dienes 5 + 6 with N‐bromosuccinimide yielded complex mixtures of 7–10. Depending on the substitution pattern at the apical carbon atoms C‐1 and C‐5 of the bicyclo[3.3.0]octadiene system, the intermediate allylic radicals are attacked preferentially either from the exo (R = Me) or from the endo face [R, R = (CH2)3, (CH2)4]. Reductive cyclisations of the dibromides 9 and exo,exo‐15 were carried out with a sonicated suspension of an activated zinc‐copper couple in tetraglyme. Sweeping of the volatile products from the reaction mixtures with nitrogen at elevated temperatures allowed the convenient isolation of the semibullvalenes 1 and barbaralane (2) in reasonable purities (92–97%) and yields (57–82%).
Synthesis of perylene‐3,4‐dicarboximides — Novel highly photostable fluorescent dyes
Authors: Feiler Leonhard , Langhals Heinz , Polborn Kurt 
Published: July 2007

AbstractPerylene‐3,4‐dicarboximides 2 are obtained by a decarboxylizing condensation of moderately sterically hindered primary amines with perylene‐3,4,9,10‐tetracarboxylic 3,4:9,10‐bisanhydride (3) in the presence of water. Perylene‐3,4‐dicarboxylic anhydride (4) is prepared by hydrolysis of the imides with KOH in tert‐butyl alcohol. The anhydride may be condensed with any primary amine to the corresponding imide. The imides are highly fluorescent and very photostable dyes.
Syntheses and conformations of persubstituted inverse calixarenes
Authors: Schätz Rolf , Weber Christian , Schilling Gerhard , Oeser Thomas , Huber‐Patz Ursula , Irngartinger Hermann , von der Lieth Claus‐W. , Pipkorn Rüdiger 
Published: July 2007

AbstractA series of ten inverse calix[n]arenes (2–11) bearing four to thirteen benzene units were prepared by starting from 3,4,5‐trimethoxybenzaldehyde followed by LC separation on silica gel. In 2–11 the substitution pattern is interchanged compared with the usual calixarenes. The conformational analysis was undertaken by variable temperature 1H‐NMR spectroscopy and by MM2 calculations. Calix[4]arene 2 is a rigid molecule and shows the 1,3‐alternate conformation which in addition was proven by X‐ray analysis. At low temperatures the calix[5]arene 3 adopts the uudod conformation, where a methyl group of one benzene unit residues in the cavity of the macrocycle. At low temperature calix[6]arene 4 forms an 1:2 equilibrium between the 1,3,5‐alternate (ududud; 4E) and the uududu (4B) conformation. Conformation 4B can be regarded as an intramolecular combination of a cone and an alternate arrangement of the benzene units. The calix[8]‐arene shows the highest ΔG* value of the series and adopts an uuududdd conformation at low temperature. The inverse calixarenes 5 and 7–11 bearing seven and nine to thirteen aromatic units, respectively, are conformationally highly flexible systems even at low temperatures.
Stereoselective synthesis of oligo(tetrahydrofurans): Linear and convergent routes to bi‐ and tertetrahydrofurans
Authors: Koert Ulrich , Stein Matthias , Wagner Holger 
Published: July 2007

AbstractThe „dimeric”︁ and „trimeric”︁ oligo(tetrahydrofurans) (oligo‐THFs) 24, 28, 32, and 38 were synthesized stereoselectively according to a linear and a convergent synthetic strategy. The oligo‐THFs thus obtained are important intermediates for the synthesis of artificial ion channels. Furthermore, they can be used in the total synthesis of Annonaceae acetogenins, a class of natural occurring oligo‐THFs with promising pharmacological properties.
Total synthesis of angucyclinones, 6. Synthesis of naturally (MM 47755; X‐14881 E) and non‐naturally occurring aromatic angucyclinones
Authors: Krohn Karsten , Khanbabaee Karamali , Micheel Jörg 
Published: July 2007

AbstractThe Diels‐Alder reactions of the naphthoquinones 1–4 with the dienes 5a–7 were investigated. The regioisomeric outcome of the adducts 10a–10g, 16, and 23 is in agreement with theoretical predictions from frontier orbital calculations. The adduct 10a was further converted to the non‐natural (e.g. 15) and the adduct 16 to the natural angucyclinones MM 47755 (19a) and X‐14881 E (22) by silicon‐oxygen exchange and photooxygenation. The addition of naphtoquinones 2 and 4 to dienes 6 and 7 afford the Diels‐Alder adducts 16 and 23, respectively, which are valuable intermediates for further transformation into non‐aromatic angucyclinones.
Biscyclopropanation of C70
Authors: Bingel Carsten , Schiffer Heinz 
Published: July 2007

AbstractThe biscyclopropanation of C70 with bromomalonate anions shows a strong preference for three regioisomers, which can be separated by column chromatography. The structures of the three regioisomers were determined by 13C‐NMR spectroscopy. The two cyclopropanation reactions take place on opposite hemispheres of C70.
A new synthetic route to the azocino[4,3‐b]indole core structure
Authors: Patir Süleyman 
Published: July 2007

AbstractThe reaction of 2 with 2‐methoxyethylamine in the presence of ZnCl2 afforded imine 3, which was reduced with NaBH4 to amine 4 without isolation. After deprotection of the carbonyl function by treatment with benzeneseleninic anhydride, ketone 5 was converted to compound 6 with 2‐oxobutyric acid and dicyclohexylcarbodiimide. The isodasycarpidone derivative 7, formed by aldol reaction of 6, represents a tetracyclic substructure of strychnos‐type alkaloids.
The Diels‐Alder route to trifluoromethyl‐substituted carbo‐ and heterocycles
Authors: Schlosser Manfred , Keller Holger 
Published: July 2007

AbstractStarting with 1,1,1‐trifluoroacetone, 3‐(trifluoromethyl)‐1‐(trimethylsilyloxy)‐1,3‐butadiene (2) has been prepared as a mixture of (Z) and (E) isomers. The diene undergoes [4 + 2] cycloaddition reactions with a variety of dienophiles affording trifluoromethyl‐substituted carbocyclic and heterocyclic compounds 7–11 in yields ranging from moderate to good.
1,4‐dicarbonyl‐2,5‐cyclohexadiene
Authors: Marquardt Ralph , Sander Wolfram , Laue Thomas , Hopf Henning 
Published: July 2007

AbstractThe mechanism of the photolysis of [2.2]paracyclophane‐1,10‐dione (9) was investigated in solution and in argon matrices. The first step of the photolysis involves α‐cleavage of the cyclophane yielding a diradical 11 which could be trapped by ethanol. In argon at 10 K the diradical rapidly splits into p‐xylylene (10) and 1,4‐dicarbonyl‐2,5‐cyclohexadiene (7) and therefore was not directly observed by spectroscopic methods. The bisketene 7 was characterized by comparison of the experimental and calculated IR spectrum.
Synthesis and electrochemical properties of 4‐phenyl‐1‐buten‐3‐yne‐1,1,2‐tricarbonitriles and tricyanoacrylates
Authors: Dulog Lothar , Körner Bernd , Heinze Jürgen , Yang Jianjun 
Published: July 2007

AbstractThe reaction of phenylacetylenes 4a–h with copper(I) acetate (5) and TCNE (tetracyanoethylene) in THF/acetonitrile gave 4‐phenyl‐1‐buten‐3‐yne‐1,1,2‐tricarbonitriles 6a–h. 4i did not react to give 6i. The phenylacetylenes 4b–i were prepared by a two‐step synthesis starting from the corresponding phenyl halides 1b–i. The tricyanoacrylates 8 were synthesized from the corresponding cyanoacetates 7, TCNE and catalytic amounts of pyridine in THF. – Cyclovoltammetric investigations showed that the butenynes 6 and the tricyanoacrylates 8 are strong electron acceptors which can be easily reduced. The radical anions 6˙− are unstable in aceto‐nitrile and react irreversibly with 6 to give oligomeric anions 6. Only 4‐(2,4,6‐trimethoxyphenyl)‐1‐buten‐3‐yne‐1,1,2‐tricarbonitrile (6h) is reduced to a radical anion 6h˙− which associates with 6h in a reversible follow‐up process to form a dimeric anion 6h. By contrast, the tricyanoacrylates 8 can be reversibly reduced to their respective radical anions and dianions.
Synthesis of glycolipids as membrane‐bound stabilizing carbohydrates
Authors: Wilhelm Falk , Chatterjee Swapan Kumar , Rattay Bernd , Nuhn Peter , Benecke Renate , Ortwein Jutta 
Published: July 2007

AbstractStereoselective synthesis of glycosides (glucosides, galactosides, mannosides, and xylosides) is reported using long‐chain alcohols with 0–4 ethoxy spacers as potential anchored cryoprotectors.
Syntheses of thymidine diphosphoglucose derivatives
Authors: Liemann Susanne , Klaffke Werner 
Published: July 2007

AbstractPer‐O‐benzoylated 3‐ and 4‐deoxy‐α‐D‐glucopyranoses 3 and 12, as well as the respective 4‐isobutyramido derivative 29 were converted into their hemiacetals, phosphitylated, and oxidized to yield anomeric mixtures of glycosyl phosphates. These partially esterified compounds were coupled with dTMP morpholidate to give after complete deblocking dTDP‐3‐deoxy‐α‐D‐glucose (11), dTDP‐4‐deoxy‐α‐D‐glucose (19) and dTDP‐4‐amino‐4‐deoxy‐α‐D‐glucose (36). 3‐Acetamido‐3‐deoxy‐α‐D‐glucopyranosyl phosphate was synthesized according to the silver diphenyl phosphate procedure and subsequently converted into dTDP‐3‐acetamido‐3‐deoxy‐α‐D‐glucose (dTDP‐N‐acetyl‐D‐kanosamine) (26) by hydrogenation and coupling with dTMP morpholidate.
Reactions of N‐sulfonylalkylamines with ynamines — formation of 2H‐1,2‐thiazete 1,1‐dioxides, novel thioketene S,S‐dioxide dimers, and other s,n‐heterocycles
Authors: Tornus Ingo , Schaumann Ernst , Mayer Roland , Adiwidjaja Gunadi 
Published: July 2007

AbstractN‐Sulfonylalkylamines 2a, b react with ynamines 3 to give primarily 2H‐1,2‐thiazete 1,1‐dioxides 4. But, except for the 4‐triphenylsilyl species 4a, b, these products are unstable and undergo electrocyclic ring opening to very reactive amidinosulfenes 5, which are transformed into different products, depending on the ynamine substituents R2. The 1,3‐dithietane 1,1,3,3‐tetraoxide 8 is formed from N‐sulfonylisopropylamine (2a) and the trimethylsilyl‐substituted ynamine 3b via amidinosulfene 5c and probably thioketene S,S‐dioxide 7. On the other hand, (isopropylamidino)sulfene 5d dimerizes to the 2H‐1,5,2‐dithiazine 9 and also gives the [2 + 4] cycloadducts 10a, 11a by reaction with 2a and ynamine 3c, respectively. In contrast, it was possible to trap phenyl‐substituted amidinosulfenes 5e‐h by addition of water or methanol.