bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calorimetric Measurements of the Complexation of Cyclosporin A, Ascomycin, Fujimycin, and Rapamycin with Lithium Chloride and with an Immunophilin
Authors: Seebach Dieter , Bossler Hans G. , Flowers Robert , Arnett Edward M. 
Published: December 2004

AbstractSolutions (2 ml) of small linear and cyclic peptides (4–11), of a peptolide containing nine amino acids and a lactate moiety (12), of the cyclic undecapeptide cyclosporin A (CS, 1), and of the macrolides ascomycin, fujimycin, and rapamycin (13–15) in THF were added to excess LiCl, LiBr, or LiClO4 (up to 3000 equiv. in 40 ml THF) in a calorimeter (calorimetric titration). The enthalpies of interaction measured are in the range of ΔH = −8 to −37 kcal/mol. A similar experiment was carried out with one of the binding proteins of cyclosporin, the human cyclophilin A, to give the thermodynamic parameters for the complexation ΔH = −16, ΔG° = −10 kcal/mol, and ΔS° = −20 cal/mol·deg. at 25° which corresponds to an equilibrium constant K = 2·107 l/mol, in good agreement with the result of independent measurements using different methods. NMR Measurements of the macrolides in (D8)THF containing LiCl show strong down‐field shifts of signals of the H‐atoms next to CO and C–OH groups in these molecules.
Radical Reactions in an X‐Irradiated Phosphaalkene: A single‐crystal ESR study
Authors: Bhat Shrinivasa N. , Berclaz Théo , Jouaiti Abdelaziz , Geoffroy Michel 
Published: December 2004

AbstractSingle crystals of 1‐[2,4,6‐tri(tert‐butyl)phenyl]‐2‐phenylphosphaethene (PPPE) and of 2D‐ and 13C‐enriched PPPE were studied by ESR after X‐ray irradiation. Two phosphorus‐centered radicals were trapped in the crystals. The first one was characterized by its 31P, 1H‐, and 13C‐hyperfine tensors, the second one exhibited coupling with 31P only. Comparison of these parameters with those predicted by ab initio calculations on some phosphinyl species indicates that these two radicals probably result, on the one hand, from an addition of a H‐atom to the C‐atom of the PC bond and, on the other, from a cyclization of the parent molecule. The proposed mechanisms are consistent with the mutual orientations of the hyperfine eigenvectors and bond directions in the undamaged molecule. A C‐centered radical which results from an addition of a H‐atom to the P‐atom of the phosphaethylene bond is also detected.
Total Syntheses of Two Self‐polymerizable Carbocyclic Analogues of 2′‐deoxyribonucleosides
Authors: Wang Jianji , Gossauer Albert 
Published: December 2004

AbstractA short regio‐ and stereoselective synthesis of two carbocyclic 3′‐deoxynucleoside analogues is described, the key step of which consists in the photosensitized addition of MeOH to a cyclopent‐2‐enone derivative. As in both cases functional groups capable to react with each other are present in the same molecule, the synthetic compounds can form polymers similar to oligonucleotides.
3‐Phenyl‐D3‐Trishomocuban‐4‐ol: Structure and Configuration
Authors: Carpy Alain J. M. , Oliver Douglas W. 
Published: December 2004

AbstractThe crystal structure of 3‐phenyl‐D3‐trishomocuban‐4‐ol (4) was determined by X‐ray crystallography (Fig. 1). Compound 4 was prepared from 8‐phenylpentacyclo[5.4.0.02,6.03,10.05,9]undecan‐8‐ol in acidic medium. This is a facile method to prepare substituted trishomocubanes with a specific configuration at C(4).
Carbamate Series of Juvenoids: Variation of the O‐alkyl substituent
Authors: Wimmer Zdenêk , S̆aman David , Nêmec Václav , Francke Wittko 
Published: December 2004

AbstractBy changing the O‐alkyl substituents of the carbamate moiety of alkyl N‐{2‐{4‐[(2‐oxocyclohexyl)methyl]phenoxy}ethyl}carbamates and subsequent transformation of the oxo group in the cyclohexyl substituent, the juvenoids 1–20 were synthesized (Scheme). The methyl (1–4), propyl (9–12), isopropyl (13–16), and prop‐2‐ynylcarbamates (17–20) were subjected to biological screening on several non‐related insect species (Tenebrio molitor, Galleria mellonella, Dysdercus cingulatus, and Pyrrhocoris apterus). Some of the juvenoids showed high biological activity and excellent selectivity with respect to target insect species (Table 2).
3′‐Amino‐Modified Nucleotides Useful as Potent Chain Terminators for current DNA sequencing methods
Authors: Herrlein Mathias K. , Konrad Renate E. , Engels Joachim W. , Holietz Torsten , Cech Dieter 
Published: December 2004

AbstractWe describe the synthesis of modified nucleoside triphosphates of the four DNA bases containing a 3′‐amino group which were prepared from the corresponding 3′‐azido derivatives. Introduction of the triphosphate and subsequent reduction of the N3 to the NH2 group led directly to the target molecules 6a–d. Furthermore, 3′‐amino‐2′,3′‐dideoxynucleoside 5′‐triphosphates proved to be potent inhibitors of the enzymatic synthesis of DNA catalyzed by the standard sequencing enzymes T7 DNA polymerase, sequenase version 2.0, Thermus aquaticus DNA polymerase, and Thermus thermophilus DNA polymerase. Both radioactive and fluorescent sequencing methods were applied successfully to the 3′‐amino‐modified terminators. Investigations in view of using these chain terminators according to Sanger's sequencing method for fluorescence labeling were done.
A Novel Approach to 2,2‐Disubstituted 1,2‐Dihydro‐4‐phenylquinolines
Authors: Walter Harald 
Published: December 2004

AbstractThe reaction of 2‐(1‐phenylvinyl)aniline and 4‐chloro‐2‐(1‐phenylvinyl)aniline with acetophenone derivatives, 1‐(naphthalen‐1‐yl)ethanone and 1‐(furan‐2‐yl)ethanone in toluene at 110–115° with toluene‐4‐sulfonic acid as a catalyst leads in good‐to‐excellent yields to the 2,2‐disubstituted 1,2‐dihydro‐4‐phenyl‐quinolines 1–18 (Scheme 1, Table). The structure of the new racemic 1,2‐dihydroquinolines 1–18 is determined by NMR spectroscopy. A reaction mechanism proceeding via a 6π‐electrocyclic rearrangement of 2‐(1‐phenylvinyl)anils 19 as the key step is proposed for the formation of these compounds (Scheme 1). The scope and limitations of the novel methods are discussed (Scheme 2).
Derivatives of (2R)‐N‐Glyoxylbornane‐10,2‐sultam and Their Use as auxiliaries in the diastereoselective spirocyclization of 2‐substituted tryptamines
Authors: Freund Ralf , Allagiannis Christos , Schönholzer Peter , Bernauer Karl 
Published: December 2004

AbstractA crude hydrate 6 and a crystalline hemiacetal 7 of glyoxylamide 4 were prepared from crotonamide 5 (Scheme 2). Particularly hemiacetal 7, but also 6 and the ‘dimer’ 8 (obtained from 7) may serve as homochiral auxiliaries. The structure of 8 was determined by X‐ray analysis. By arenesulfonyl halides, tryptimines 12–14 of 4 were diastereoselectively transformed into spirotricycles 15–17 and 19.
A Concise Synthesis of (E)‐ and (Z)‐Neomanoalides
Authors: Jefford Charles W. , Rossier Jean‐Claude , Boukouvalas John , Huang Pingzhong 
Published: December 2004

AbstractThe first synthesis of (Z)‐neomanoalide (4) and an improved synthesis of its (E)‐isomer 3 was accomplished in a concise, regiocontrolled manner by exploiting 2‐[(tert‐butyl)dimethylsiloxy]‐4{[(tert‐butyl)dimethylsiloxy]‐methyl}furan (6) as the key reagent. Lithiation of 6 and subsequent reaction with the (2Z)‐ or (2E)‐isomer of (6E)‐3‐{[(tert‐butyl)dimethylsiloxy]methyl}‐7‐methyl‐9‐(2′,6′,6′‐trimethylcyclohex‐1′‐enyl)nona‐2,6‐dienyl bromide (5), followed by hydrolysis, afforded the corresponding neomanoalide.
Face selectivity of the Diels‐Alder additions and cheletropic additions of sulfur dioxide to 2‐ vinyl‐7‐oxabicyclo[2.2.1]hept‐2‐ene derivatives
Authors: Meerpoel Lieven , Vrahami Maria‐Miranda , Deguin Brigitte , Vogel Pierre 
Published: December 2004

AbstractRacemic 6‐ethenyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (23), 5‐ethenyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (25) and their ethylene acetals 24 and 26, respectively, were derived from the Diels‐Alder adduct of furan to 1‐cyanovinyl acetate (27). The Diels‐Alder additions of 26 to dimethyl acetylenedicarboxylate, to methyl propynoate, to N‐phenylmaleimide, and to methyl acrylate were highly exo‐face selective, as were the cycloadditions of methyl propynoate to dienones 23 and 25 and of dimethyl acetylenedicarboxylate to ethylenedioxy‐diene 24. The cheletropic additions of SO2 to 23–26 gave exclusively the corresponding sulfolenes 57–60 resulting from the exo‐face attack of the semicyclic dienes under conditions of kinetic and thermodynamic control.
A Short Synthesis of (−)‐Carbovir
Authors: Hildbrand Stefan , Troxler Thomas , Scheffold Rolf 
Published: December 2004

Abstract(–)‐Carbovir ((–)‐1) was synthesized via the cyclic carbonate 2 in four steps starting from enantiomerically enriched (–)‐(S)‐(cyclopent‐2‐enyl)methanol ((–)‐3).
Synthesis and Structure‐Activity Relationships of Juvenoids Derived from 2‐(4‐hydroxybenzyl)cycloalkan‐1‐ones
Authors: Rejzek Martin , Wimmer ZdenêK , Šaman David , Říčánková Michaela , Nêmec Václav 
Published: December 2004

AbstractJuvenoids 16–30, 32, 36, 38–41, 44–46, and 49–56 containing carbamate, carbonate, and urea moieties in the molecule were synthesized and subjected to a biological screening (Schemes 2–7, Table 2). Carbamate juvenoids 1–4 were used as reference compounds for a detailed structure‐activity study of their analogues. A clear relationship between the nature of the side chain functional group and the biological activity was found. Surprisingly, not only the juvenoids 1–4 but also 38–41, the compounds with a reversed carbamate N,O‐substitution pattern, showed very promising biological activity. In contrast, the carbonate and urea derivatives displayed a remarkably low activity. The relationship between the size and substitution at atoms C(2) and C(3) of the saturated ring and the biological activity is very complex and is still not completely understood.
Umsetzung von Diazoessigsäure‐ethylester mit 1,3‐Thiazol‐5(4H)‐thionen
Authors: Kägi Martin , Mlostoń Grzegorz , Linden Anthony , Heimgartner Heinz 
Published: December 2004

Reaction of Ethyl Diazoacetate with 1,3‐Thiazole‐5(4H)‐thionesReaction of ethyl diazoacetate (2a) and 1,3‐thiazole‐5(4H)‐thiones 1a,b in Et2O at room temperature leads to a complex mixture of the products 5–9 (Scheme 2). Without solvent, 1a and 2a react to give 10a in addition to 5a–9a. In Et2O in the presence of aniline, reaction of 1a,b with 2a affords the ethyl 1,3,4‐thiadiazole‐2‐carboxylate 10a and 10b, respectively, as major products. The structures of the unexpected products 6a, 7a, and 10a have been established by X‐ray crystallography. Ethyl 4H‐1,3‐thiazine‐carboxylate 8b was transformed into ethyl 7H‐thieno[2,3‐e][1,3]thiazine‐carboxylate 11 (Scheme 3) by treatment with aqueous NaOH or during chromatography. The structure of the latter has also been established by X‐ray crystallography. In the presence of thiols and alcohols, the reaction of 1a and 2a yields mainly adducts of type 12 (Scheme 4), compounds 5a,7a, and 9a being by‐products (Table 1). Reaction mechanisms for the formation of the isolated products are delineated in Schemes 4–7: the primary cycloadduct 3 of the diazo compound and the CS bond of 1 undergoes a base‐catalyzed ring opening of the 1,3‐thiazole‐ring to give 10. In the absence of a base, elimination of N2 yields the thiocarbonyl ylide A′, which is trapped by nucleophiles to give 12. Trapping of A′, by H2O yields 1,3‐thiazole‐5(4H)‐one 9 and ethyl mercaptoacetate, which is also a trapping agent for A′, yielding the diester 7. The formation of products 6 and 8 can be explained again via trapping of thiocarbonyl ylide A′, either by thiirane C (Scheme 6) or by 2a (Scheme 7). The latter adduct F yields 8 via a Demjanoff‐Tiffeneau‐type ring expansion of a 1,3‐thiazole to give the 1,3‐thiazine.
Synthese einer Calicen‐Vorstufe für Retro‐Diels‐Alder‐Reaktionen
Authors: Mühlebach Michel , Neuenschwander Markus 
Published: December 2004

Synthesis of a Calicene Precursor for Retro‐Diels‐Alder ReactionsIn view of retro‐Diels‐Alder reactions (RDA reactions), the calicene precursor 9 has been synthesized in a comparably simple four‐step synthesis by dibromocarbene addition at dibenzobarrelene (10 → 11, 44%), halogenlithium exchange followed by reaction with cyclopentenone (11→12, 91%) and H2O as well as HBr elimination (12→14→9, 43%) (Scheme 5). First experiments with respect to the thermal behavior of 9 show that, although RDA reaction seems to be relatively easily occurring according to the results of ‘Curie‐Point’ pyrolysis, only anthracene and no calicene 2 has been detected so far.
Total Synthesis of Racemic and Optically Active Compounds Related to Physostigmine and Ring‐C Heteroanalogues from 3‐[2′‐(dimethylamino)ethyl]2,3‐dihydro‐5‐methoxy‐1,3‐dimethyl‐1H‐indo l‐2‐ol
Authors: Pei Xue‐Feng , Greig Nigel H. , Flippen‐Anderson Judith L. , Bi Sheng , Brossi Arnold 
Published: December 2004

AbstractOxindole 11, obtained on 3‐[2′‐(dimethylamino)ethyl]alkylation of oxindole 12, yielded, on stereoselective reduction with sodium dihydridobis(2‐methoxyethoxy)aluminate, aminoalcohol 8 (Scheme 2). The quaternary methiodide 10, obtained from 8 with MeI, gave, in nucleophilic displacements concurring with a Hofmann elimination, (±)‐esermethole 6, (±)‐5‐O‐methylphysovenol (14), (±)‐5‐O‐methyl‐1‐thiaphysovenol (15), and (±)‐1‐benzyl‐1‐demethylesermethole (16). Syntheses of (±)‐1‐benzyl‐1‐demethylphenserine (18), (±)‐1‐demethylphenserine (19), and (±)‐phenserine (4) from 6 and 16 are described. Optically active 8a and 8b, obtained by chemical resolution, similarly gave the enantiomers 6a and 14a–16a of the (3aS)‐series (prepared earlier from physostigmine (1a)) and their (3R)‐enantiomers. The anticholinesterase activity of (±)‐4, (±)‐18, and (±)‐19 was compared with that of their optically active enantiomers.
Triplet Energy of 2, 2‐Dimethylisoindene from Electron‐Energy‐Loss Spectroscopy and Photoinduced Triplet Energy Transfer
Authors: Allan Michael , Asmis Knut R. , Houar Sarah El , Haselbach Edwin , Capponi Marco , Urwyler Bernhard , Wirz Jakob 
Published: December 2004

AbstractThe excited electronic states of 2, 2‐dimethylisoindene (1) have been studied by electron‐energy‐loss spectroscopy. Its vertical gas‐phase triplet (13B2), and singlet (11B2) excitation energies are 1.61 and 3.19 eV, respectively. The excited states are thus lowered by 0.49 eV and 1.21 eV, respectively, when compared to the corresponding states of (all‐E)‐octatetraene, which serves as a reference compound. These shifts are partially reproduced by ZINDO calculations. The spectra give no evidence for a 21Ag state below the 11B2 state, but this lack of observation does not exclude its existence. The lowest triplet state T1(1) was further characterized by flash photolysis. T1(1) was observed as a transient intermediate, λ ≤ 350 nm, with a lifetime of 8 m̈s in degassed hexane. The adiabatic excitation energy of T1(1) was bracketed to the range of 1.1 ± 0.1 eV by energy‐transfer experiments. Relationships between the energies of the lowest excited singlet and triplet states of 1 and the lowest excited doublet state of its radical cation \documentclass{article}\pagestyle{empty}\begin{document}${1}^{+\kern0pt {.}}$\end{document} – essentially a non‐Koopmans' state – are discussed.
Synthese von Phosphinico‐Analog des Pantetheins
Authors: Neidlein Richard , Li Sheng 
Published: December 2004

Synthesis of Phosphinico Analogues of PantetheineThe synthesis of phosphinico analogues 9a–c of pantetheine is described where the carbonyl group of one of the amide linkage is replaced by a methyl‐, ethyl‐, or phenylphosphinoyl group.
Synthesis of Chiral Starburst Dendrimers from PHB‐Derived Triols as Central Cores
Authors: Seebach Dieter , Lapierre Jean‐Marc , Greiveldinger Guy , Skobridis Konstantinos 
Published: December 2004

AbstractChiral triols 1–3 (‘tris(hydroxymethyl)methane’ derivatives), prepared from (R)‐3‐hydroxybutanoic acid and aldehydes, are used as center pieces of dendrimers. The triols may be employed as such or after attachment of spacers containing alkyl or aryl moieties (see 5 and 7). The branches combined with the original or elongated triols are those first reported by Fréchet (9–12, benzyl ethers of 3,5‐dihydroxybenzyl alcohol and bromide). In this way, 1st‐, 2nd‐, and 3rd‐generation chiral dendrimers without (13–15), or with aliphatic (16–18) or aromatic (19–21) spacers are prepared. The molecular weights range from 447 to 2716 Dalton. Two of the chiral triols, i.e., 2 and 3, are used as center pieces for chiral dendrimers containing 6 NH2, or 6 and 12 NO2 groups on the periphery (22–27), with 3,5‐dinitrobenzoyl chloride as the branching unit. All compounds thus synthesized are of course monodisperse and are fully characterized. In some cases, the optical activity of the dendrimers indicates that conformationally chiral substructures might be present. The NH2‐ and NO2‐substituted compounds avidly clathrate smaller molecules; they are sorbents exchanging host molecules through the gas phase.
Stability of Charge‐Transfer Complexes of CS2 with PH3 and its derivatives: Ab initio MRSDCI/CASSCF Study
Authors: Zahradník Rudolf , Jungwirth Pavel , Urban Jiří , Polášek Martin 
Published: December 2004

AbstractWhile trialkylamines and dialkyl(phenyl)amines do not react with CS2 in the sense of an addition reaction, the analogous phosphines react smoothly. Attempts to interpret the reaction course on the basis of semiempirical, HF, MP2, and MP4 calculations of energy changes failed completely. To understand why Me3P or Me2PhP react so vigorously (liquid phase, 300 K) with CS2, CASSCF and MRSDCI calculations must be carried out.
Thermal and Ru‐catalyzed Reactions of Styryl‐Substituted Azulenes with Dimethyl Acetylenedicarboxylate
Authors: Briquet Anne Andrée Sophie , Hansen Hans‐Jürgen 
Published: December 2004

AbstractThe thermal reaction of 1‐[(E)‐styrl]azulenes with dimethyl acetylenedicarboxylate (ADM) in decalin at 190–200° does not lead to the formation fo the corresponding heptalene‐1,2‐dicarboxylates (Scheme 2). Main products are the corresponding azulene‐1,2‐dicarboxylates (see 4 and 9), accompanied by the benzanellated azulenes trans‐10a and trans‐11, respectively. The latter compounds are formed by a Diels‐Alder reaction of the starting azulenes and ADM, followed by an ene reaction with ADM (cf. Scheme 3). The [RuH2(PPh3)4]‐catalyzed reaction of 4,6,8‐trimethyl‐1‐[(E)‐4‐R‐styryl]azulenes (R=H, MeO, Cl; Scheme 4) with ADM in MeCN at 110° yields again the azulene‐1,2‐dicarboxylates as main products. However, in this case, the corresponding heptalene‐1,2‐dicarboxylates are also formed in small amounts (3–5%; Scheme 4). The benzanellated azulenes trans‐10a and trans‐10b are also found in small amounts (2–3%) in the reaction mixture. ADM Addition products at C(3) of the azulene ring as well as at C(2) of the styryl moiety are also observed in minor amounts (1–3%). Similar results are obtained in the [RuH2(PPh3)4]‐catalyzed reaction of 3‐[(E)‐styryl]guaiazulene ((E)‐8; Scheme 5) with ADM in MeCN. However, in this case, no heptalene formation is observed, and the amount of the ADM‐addition products at C(2) of the styryl group is remarkably increased (29%). That the substitutent pattern at the seven‐membered ring of (E)‐8 is not responsible for the failure of heptalene formation is demonstrated by the Ru‐catalyzed reaction of 7‐isopropyl‐4‐methyl‐1‐[(E)‐styryl]azulene ((E)‐23; Scheme 11) with ADM in MeCN, yielding the corresponding heptalene‐1,2‐dicarboxylate (E)‐26 (10%). Again, the main product is the corresponding azulene‐1,2‐dicarboxylate 25 (20%). Reaction of 4,6,8‐trimethyl‐2‐[(E)‐styryl]azulene ((E)‐27; Scheme 12) and ADM yields the heptalene‐dicarboxylates (E)‐30A/B, purely thermally in decalin (28%) as well as Ru‐catalyzed in MeCN (40%). Whereas only small amounts of the azulene‐1,2‐dicarboxylate 8 (1 and 5%, respectively) are formed, the corresponding benzanellated azulene trans‐29 ist found to be the second main product (21 and 10%, respectively) under both reaction conditions. The thermal reaction yields also the benzanellated azulene 28 which is not found in the catalyzed variant of the reaction. Heptalene‐1,2‐dicarboxylates are also formed from 4‐[(E)‐styryl]azulenes (e.g. (E)‐33 and (E)‐34; Scheme 14) and ADM at 180–190° in decalin and at 110° in MeCN by [RuH2(PPh3)4] catalysis. The yields (30%) are much better in the catalyzed reaction. The formation of by‐products (e.g. 39–41; Scheme 14) in small amounts (0.5–5%) in the Ru‐catalyzed reactions allows to understand better the reactivity of zwitterions (e.g. 42) and their triyclic follow‐up products (e.g. 43) built from azulenes and ADM (cf. Scheme 15).
Synthesis of Functionalized Cycloprop[f]indenes via the Carbene Addition Route
Authors: Müller Paul , Miao Zhongshan 
Published: December 2004

AbstractThe synthesis of 4,5‐dihydro‐1H,3H‐cycloprop[f]inden‐4‐ol (1) and diethyl 4,5‐dihydro‐1H,3H‐cycloprop[f]‐indene‐4,4‐dicarboxylate (26) starting from diene 4 is described. The cyclopentene ring is constructed by condensation of diethyl malonate to the dibromide 21. The key‐step in the synthesis of 1 consists in a twofold Curtius degradation of 22, with subsequent reduction of the carbonyl group and aromatization. The skeleton of the isomer 31 is synthesized via cycloaddition of butadiene to cyclopent‐4‐ene‐1,3‐dione (7) and addition of dichlorocarbene to the adduct 27 after ketalisation. The attempted synthesis of dihydrocycloprop[f]indene (2) by base‐induced elimination of several appropriately substituted precursors failed.
C2‐Symmetric Bicyclic Diols as Chiral Ligands in the titanate‐catalyzed enantioselective addition of alkylzinc reagents to aldehydes
Authors: Waldmann Herbert , Weigerding Michael , Dreisbach Claus , Wandrey Christian 
Published: December 2004

AbstractEnantiomerically pure C2‐symmetric 1,4‐diols embodying bicyclic C‐frameworks were synthesized by means of asymmetric carbo‐Diels‐Alder reactions as key steps (Scheme 1). They were investigated as chiral ligands in the enantioselective addition of ZnEt2 to aromatic aldehydes. In the presence of 20–40 mol‐% of the titanates formed from these diols and [Ti(i‐PrO)4] at −78°, the respective 1‐arylpropanols were obtained with enantiomer ratios up to 93:7 (Scheme 2, Table).
Einkristall‐Strukturen eines Donator‐Akzeptor‐substituierten Cyclopentadiens, seines Kations und seines dimeren Anions: Verschiedenartige Störungen eines Kohlenstoff‐Fünfringes
Authors: Bock Hans , Nick Sabine , Näther Christian , Bats Jan W. 
Published: December 2004

Single‐Crystal Structures of a Donor‐Acceptor‐Substituted Cyclopentadiene, Its Cation and Its Anion Dimer: Different Distortion of a Five‐Membered Carbon Ring1,4‐Dimethyl‐2,3,4,6‐tetrahydro‐1 H‐cyclopentapyrazine‐5,7‐dicarbonitrile, its molecular cation, and its dimer dianion, generated by hydride abstraction or deprotonation, and crystallized, differ remarkably in their structures: the five‐membered ring in the neutral compound is of (Z)‐butadiene‐type, whereas, in the tetrafluorborate salt, a peripheric NCCCCCN⊕ cyanine distortion occurs and in the sodium derivatives, solvated by either one or two 1,2‐dimethoxyethane molecules, a cyclopentadienyl anion is formed. The structural perturbations induced by changing molecular charges are rationalized by extensive MNDO calculations, which on geometry optimization, reproduce the experimental structures and, in addition, provide charge distributions, further confirming the nN/π and π/π interactions already recognizable from the structural parameters.