bluuebunny/crossref_metadata_2025_split huggingface dataset:
Collision‐Induced Decomposition (CID) of Triangular [Mo3S7‐xSex]4+ Complexes (x = 0,3,7). A liquid SIMS and FTMS/MS study of [Mo3S7‐xSex(Et2NCS2)3] +
Authors: Hegetschweiler Kaspar , Caravatti Pablo , Fedin Vladimir P. , Sokolov Maxim N. 
Published: December 2004

Abstract[Mo3S(S2)3(dtc)3]I, [Mo3S(SeS)3(dtc)3](dtc), and [Mo3Se(Se2)3(dtc)3](dtc) (dtc = N,N‐diethyldithiocarbamate) were investigated by liquid SIMS‐FTMS. The fragmentation pathways were essentially the same for the three compounds and can be explained by two types of fragmentation processes: stepwise abstraction of S/Se atoms as exemplified by the series [Mo3Xz(dtc)3]+ (4 ⩽ z ⩽ 7, X = S, Se), and ligand dissociation, as indicated by the generation of [Mo3Xz(dtc)2]+ (5 ⩽ z ⩽ 7, X = S, Se). The exclusive elimination of the Se‐atoms from [Mo3S(Sax‐Seeq)3(dtc)3]+ confirmed the inequivalent reactivity of the bridging atoms in axial and equatorial position as observed in previous studies. Collision‐induced decomposition (CID) of [Mo3S7(dtc)3]+ (1), [Mo3S6(dtc)3]+ (2), [Mo3S(Sax–Seeq)3(dtc)3]+ (3), and [Mo3Se7(dtc)3]+ (4) revealed distinctly different fragmentation reactions for the SIMS and CID mode. CID of 1, 3, and 4 resulted in a two‐step reaction with the exclusive elimination of diatomic molecules XY (X,Y = S/Se). In the case of 3, the selective elimination of Se2 indicated the abstraction of two Se‐atoms located in equatorial positions of two different bridging groups. This result is discussed in terms of mechanisms, based on labile MXeq and inert MXax bonds with an intramolecular formation of a X4 fragment prior to the elimination of X2.
Di(tert‐butyl)diazomethan: Thermische Zersetzung und Einelektronen‐Redox‐Reaktionen
Authors: Bock Hans , Berkner Bodo , Hierholzer Bernhard , Jaculi Dieter 
Published: December 2004

Di(tert‐butyl)diazomethane: Thermal Decomposition and One‐Electron Redox Reactions.Di(tert‐butyl)diazomethane is a potential precursor for the still unknown, presumably sterically overcrowded tetrakis(tert‐butyl)ethane and, therefore, re‐investigated. Its (Hel) photoelectron spectrum exhibits a low first vertical ionization energy of only 7.45 eV. Based on the ionization pattern, both the thermal decomposition above 600 K under nearly unimolecular conditions as well as the N2 elimination at the surface of contacts, [Nix/C]∞, [Rh4(CO)12/SiO2]∞, [Rhx/SiO2]∞, and [Ag2CO3]∞ are analyzed in a flow‐system. Heterogeneously catalyzed, N2 is split off already at room temperature, but in contrast to results for sterically less shielded diazo compounds, no dimer is formed, and only mixtures of known di(tert‐butyl)carbene‐isomerization products are isolated. Cyclic voltammetry at 233 K using a glassy carbon electrode proves a reversible oxidation followed by N2 elimination at higher temperatures and an irreversible reduction. On chemical oxidation, however, no paramagnetic species can be detected, whereas chemical reduction at a potassium metal mirror in a THF solution containing (2.2.2)cryptand, yields the radical anion characterized by ESR spectroscopy. Without a cation‐chelating ligand, the radical anion of a hitherto unknown dimer, ((CH3)3C)2CNNNNC(C(CH3)3) 2' ⊖, is generated, which dissociates at higher temperature, forming ((CH3)3C)2N2' ⊖. This one‐electron reduction product of di(tert‐butyl)diazomethane can also be detected after quickly warming up a solution containing presumably the radical anion of the triphenylphosphane adduct ((CH3)3C)2CNNPPh3' ⊖. In one of these reduction reactions, a N2 elimination is observed.
Reaktion von 2‐Diazopropan mit 1,3‐Thiazol‐5(4H)‐thionen
Authors: Mlostoń Grzegorz , Heimgartner Heinz 
Published: December 2004

Reaction of 2‐Diazopropane and 1,3‐Thiazole‐5(4H)‐thionesAt 0°, 1,3‐thiazoles 1 and 2‐diazopropane in pentane or MeOH undergo a smooth 1,3‐dipolar cycloaddition to give spirocyclic 2,4‐dihydro‐1,3,4‐thiadiazoles 6 (Scheme 3). Elimination of N2 occurs already at 20°, yielding spirocyclic thüranes 7. At room temperature, the latter decompose slowly to give 4,5‐dihydro‐5‐isopropylidene‐1,3‐thiazoles 8. The desulfurization 7 → 8 can be accelerated by heating or by addition of trimethyl phosphite. The intermediate of the N2 elimination of 6 is a thiocarbonyl ylide D which can be trapped with the reactive dipolarophiles thiobenzophenone and fumarodinitrile (Scheme 4). In the absence of these trapping reagents, D undergoes ring closure to thüranes 7. The cycloaddition of D and a second molecule of 1, the so‐called Schönberg reaction, is not observed.
Synthese von (±)‐Muscopyridin über eine C‐ZIP‐Ringerweiterungsreaktion
Authors: Hadj‐Abo Ferrid , Hesse Manfred 
Published: December 2004

Synthesis of (±)‐Muscopyridine via C‐ZIP Ring EnlargementTreatment of 4‐(1‐nitro‐2‐oxocyclododec‐1‐yl)butanal (1) and of its methyl derivative 5 with pentylamine in EtOH at room temperature gave the ring‐enlarged aminomethylidene derivatives 6 and 7, respectively (Scheme 1). After hydrolysis of the aminomethylidene group in 6 and 7 and deformylation followed by a reductive Nef‐type reaction, the macrocyclic diketones 10 and 11, respectively, were obtained. They were transformed by a modified Hantzsch procedure to the title compound (±)‐muscopyridine (13) and normuscopyridine (12), respectively.
Synthetic Analogues of Naturally Occurring Spider Toxins
Authors: Kovács Lajos , Hesse Manfred 
Published: December 2004

AbstractNaturally occurring spider toxins are potent inhibitors of glutamate receptors of the central nervous system and have the general structure (hetero)arylacyl→aminoacyl(I)→polyamine→aminoacyl(II) (the arrow indicates the direction of an amide linkage). In the present paper, the synthesis of the ten spider‐toxin analogues 13, 18, 21, 28, 35, 37, 39, 41, 45, and 53 are reported (Schemes 1–12). These compounds differ in their subunits and, in some cases, in the sequence of these moieties.
Electrospray‐Ionization Mass Spectrometry: Detection of a radical cation present in solution: New results on the chemistry of (tetrahydropteridinone)‐metal complexes
Authors: Schäfer Andrea , Fischer Berthold , Paul Henning , Bosshard René , Hesse Manfred , Viscontinif Max 
Published: December 2004

AbstractThis paper marks the first reported detection of radical cations by Electrospray‐Ionization Mass Spectrometry (ESI‐MS). Electron Spin Resonance (ESR) measurements have proven that the detected radical cation existed already in solution and has not been generated by the electrospray ionization technique. However, we observed that the radical cation can be generated by changes in the ionization conditions. A molar mixture of 2‐amino‐5,6,7,8‐tetrahydro‐5‐methylpterin‐4(4H)‐one dihydrochloride ( = 5,6,7,8‐tetrahydro‐N(5)‐methylpterin‐2 HCl, N(5)‐MTHP‐2 HCl), and tris(pentane‐2,4‐dionato)iron(III) in MeCN at pH 2–3 leads to the formation of a [bis(pentane‐2,4‐dionato)(2‐amino‐5,6,7,8‐tetrahydro‐5‐methylpteridin‐4 (4H)‐one)]iron complex ( = [bis(pentane‐2,4‐dionato) (5,6,7,8‐tetrahydro‐N(5)‐methylpteridin)]iron complex) which can be detected by ESI‐MS. The results suggest that this complex might be an FeII radical cation, which could possibly be a suitable model complex for the active center of the phenylalanine hydroxylase. In the same solution, the stable radical cation of N(5)‐MTHP is identified by ESI‐MS and ESR.
High‐Yield Formation of Arbutin from Hydroquinone by Cell‐Suspension Cultures of Rauwolfia serpentina
Authors: Lutterbach Ralf , Stöckigt Joachim 
Published: December 2004

AbstractHigh‐density cell‐suspension cultures of Rauwolfia serpentina cultivated in a nutrition medium optimized for the production of the glucoalkaloid raucaffricine synthesize hydroquinone glycosides from continuously added hydroquinone with a total yield of 23.87 g/1 (18 g/1 of arbutin and 5.87 g/1 of a hydroquinone diglycoside) in 7 days. This arbutin production is by far the highest formation of a natural product by plant‐cell‐culture systems reported to date.
Synthesis of New Glycerolipids Linked to Hydroxamate Derivatives Designed for Two‐Dimensional Crystallization of Aminopeptidase M
Authors: Altenburger Jean‐Michel , Lebeau Luc , Mioskowski Charles , Schirlin Daniel 
Published: December 2004

AbstractThe synthesis of glycerolipids linked to hydroxamate derivatives designed for two‐dimensional crystallization of aminopeptidase M is reported. The lipid moieties are readily obtained using a convergent pathway. Their structure allows the introduction of a wide variety of ligands of biological interest.
Oxidative Coupling Of 2‐Alkyl‐6,6‐dimethylpentafulvenyl Anions
Authors: You Shaochun , Neuenschwander Markus 
Published: December 2004

AbstractCucl2‐Induced oxidative coupling of 2‐(tert‐butyl)‐6,6‐dimethylpentafulvenyl anion 9 predominantly takes place at C(7) and C(5) to give [7–7] and [7–5] coupling products 15 and 16 in 35 and 47% yields, respectively (Scheme 3) whose structures are elucidated from 1D‐ and 2D‐NMR analysis. Compared with the product distribution observed for 6,6‐dimethylpentafulvenyl anion 2 (Scheme 1), no coupling at C(2)/C(3) of 9 is observed. This means that, besides electronic effects, steric effect are also important in oxidative couplings of fulvenyl anions. The same couplings occur in the case of 2,3‐bis(6,6‐dimethylfulven‐2‐yl)‐2,3‐dimethylbutane dianion 10 as well but, due to electronic as well as conformational effects (Scheme 5), intermolecular coupling (to give polymers 17, Scheme 4) is strongly favored over intermolecular coupling. Mechanisms explaining base‐catalyzed isomerization 15a ⇄ 15b ⇄ 15c (Scheme 6) as well as isomerization 16a ⇄16b (Scheme 7) are proposed.
Internal Nucleophilic Termination in Acid‐Mediated Polyene Cyclisations: Synthetic access to methyle homologs of (±)‐Ambrox® and its diastereoisomers
Authors: Snowden Roger L. , Eichenberger Jean‐Claude , Giersch Wolfgang , Thommen Walter , Schulte‐Elte Karl H. 
Published: December 2004

AbstractTreatment of ten monocyclic dienols 8–11 with an excess of fluorosulfonic acid in 2‐nitropropane at −90° afforded diastereoisomeric mixtures of racemic tricyclic ethers 12–14 in 81–91% yield (see tables 1 and 2). These transformations represent further examples of biomimetic acid‐mediated cyclisations in which an OH group serves as the internal nucleophilic terminator. A non‐synchronous process is postulated, and the examples described strongly re‐inforce our working mechanistic hypothesis, whereby the stereochemical course of cyclisation is directed by the orientation of the side chain vicinal to the intermediate cyclohexyl cation (see Schemes 4 and 5). It is also demonstrated that the efficiency of this process is independent of the nature of the OH group, which may be primary, secondary, or tertiary. In addition, the organoleptic properties of 12–14, Me homologs of known odorants such as Ambrox® ((−)‐3a) and its diastereoisomer, are briefly discussed.
Synthese von Alkylphenolen und ‐pyrocatecholen aus Plectranthus albidus (Labiatae)
Authors: Bürgi Christoph , Liu Gui , Rüedi Peter 
Published: December 2004

Synthesis of Alkylphenols and ‐catechols from Plectranthus albidus (Labiatae)In the preceding paper, we described the isolation and structure elucidation of a series of even‐numbered phenol‐ or pyrocatechol‐derived 1‐arylalkane‐5‐ones. To establish the assigned structures unambiguously and to have larger quantities available for physiological testing, the following compounds were prepared: in the alkylphenol series, 1‐(4′‐hydroxyphenyl)tetradecan‐5‐one (2a), 1‐(4′‐hydroxyphenyl)hexadecan‐5‐one (2b), and 1‐(4′‐hydroxyphenyl)octadecan‐5‐one (2c); in the alkylcatechol series, 1‐(3′,4′‐dihydroxyphenyl)decan‐5‐one (3a; not isolated as a natural compound), 1‐(3′,4′‐dihydroxyphenyl)dodecan‐5‐one (3b), 1‐(3′,4′‐dihydroxyphenyl)tetradecan‐5‐one (3c), 1‐(3′,4′‐dihydroxyphenyl)hexadecan‐5‐one (3d), 1‐(3′,4′‐dihydroxyphenyl)octadecan‐5‐one (3e), and 1‐(3′,4′‐dihydroxyphenyl)icosan‐5‐one (3f); in the alkenylphenol series, (Z)‐1‐(4′‐hydroxyphenyl)octadec‐13‐en‐5‐one (4a) and (E)‐1‐(4′‐hydroxyphenyl)octadec‐13‐en‐5‐one (4b); in the alkenylcatechol series, (E,E)‐1‐(3′,4′‐dihydroxyphenyl)deca‐1,3‐dien‐5‐one (1) and (Z)‐1‐(3′,4′‐dihydroxyphenyl)octadec‐13‐en‐5‐one (5). All compounds proved to be identical with the previously assigned structures. Compound 1 was synthesized by regioselective aldol condensation of heptan‐2‐one with (E)‐1‐(3′,4′‐dimethoxyphenyl)prop‐2‐enal (6d; Scheme 1), the phenols 2a–c and the catechols 3a–f by addition of the corresponding alkyl Grignard reagent to 5‐(4′‐methoxyphenyl)‐ or 5‐(3′,4′‐dimethoxyphenyl)pentanal (17c and 18c, resp.; Scheme 4), and the olefins 4a, 4b and 5 from 17c or 18c via the 9‐O‐silyl‐protected 13‐(4′‐methoxyphenyl)‐ or 13‐(3′,4′‐dimethoxyphenyl)tridecanals (26 and 27, resp.) and Wittig olefination as the key steps (Scheme 5).
Umsetzung von 3‐Amino‐2H‐azirinen mit Salicylohydrazid
Authors: Magirius Florian , Linden Anthony , Heimgartner Heinz 
Published: December 2004

Reaction of 3‐Amino‐2H‐azirines with Salicylohydrazide3‐Amino‐2H‐azirines 1a–g react with salicylohydrazide (7) in MeCN at 80° to give 2H, 5H‐1,2,4‐triazines 10, 1,3,4‐oxadiazoles 12 and, in the case of 1d, 1,2,4‐triazin‐6‐one 11a (Scheme 3). The precursor of these heterocycles, the amidrazone of type 9, except for 9c and 9g, which could not be isolated, has been found as the main product after reaction of 1 and 7 in MeCN at room temperature. 3‐(N‐Methyl‐N‐phenylamino)‐2‐phenyl‐2H‐azirin (1g) reacts with 7 to give mainly the aromatic triazines 15b1 and 15b2. In this case, two unexpected by‐products, 16 and salicylamide (17), occurred, probably by disproportionation of a 1:1 adduct from 1g and 7 (Scheme 8). Oxidation of 10f with DDQ leads to the triazine 15a. The structure of 10c, 11a, 12c, 13 (by‐product in the reaction of 1b and 7), the N′‐phenylureido derivative 14 of 9d (Scheme 4) as well as 15b2 has been established by X‐ray crystallography. The ratio of 10/12 as a function of substitution pattern in 1 and solvent has been investigated (Tables 1, 3, 4, and 7). A mechanism for the formation of 10 and 12 is proposed in Scheme 7.
Oxidative Coupling of 6,6‐Dimethylpentafulvenyl Anion
Authors: You Shaochun , Neuenschwander Markus , Huber Hanspeter 
Published: December 2004

AbstractOxidative treatment of anion 11 (obtained by deprotonation of 6,6‐dimethylpentafulvene 10, Scheme 3) with CuCl2 gives a very complex mixture of coupling products 13 (18%), 14 (16%), 15 (36%), 16 (5%), and 17 (6%) (Scheme 4 and Table 2). These results show that the reactive intermediate obtained by oxidation of 11 (which is believed to be the fulvenyl radical 12) has several reactive sites. According to the experiments, reactivity is decreasing in the series C(7) > C(2)/C(3) > C(5) > C(1)/C(4) (Table 2), while simple frontier‐orbital considerations would suggest the sequence C(7) > C(5) > C(2)/C(3) > C(1)/C(4). The results suggest that SOMO‐SOMO interaction of the approaching fulvenyl radicals 12 is the central effect governing regioselectivity and product distribution, while Coulomb and steric interactions are secondary effects (Table 4).
A New Helicopodand: Molecular Recognition of Dicarboxylic Acids with High Diastereoselectivity
Authors: Owens Linda , Thilgen Carlo , Diederich François , Knobler Carolyn B. 
Published: December 2004

AbstractThe helicopodand (PM)‐2 is prepared following the photocyclodehydrogenation route to helicenes (Scheme). At the ends of a [7]helicene backbone, this acyclic receptor (‘podand’) possesses a H‐bonding recognition site shaped by two convergent N‐(pyridin‐2‐yl)carboxamide (CONH(py)) units. In the crystal of diethyl [7]helicene‐2,17‐dicarboxylate ((PM)‐3), a direct synthetic precursor of 2, molecules of the same chirality form stacks, and two stacks of opposite chirality are interlocked in a pair having average face‐to‐face aromatic contacts of 3.82 Å between benzene rings of different enantiomers (Fig. 2). In contrast, two conformations are observed in the crystal structure of 2, one with both CONH(py) residues pointing with their H‐bonding centers NH/N away from the binding site (‘out‐out’) and a second (‘in‐out’) with one of the two CONH(py) residues pointing towards the binding site (‘in’; Fig. 4). While no H‐bonding network propagates throughout the crystal, enantiomers of 2 in the different conformations ‘out‐out’ and ‘in‐out’ form H‐bonded pairs that are further stabilized by a H‐bond to one molecule of CHCl3. In the productive ‘in‐in’ conformation, 2 forms stable 1:1 complexes with α,ω‐dicarboxylic acids in CHCl3, and a diastereoselectivity in complexation of Δ(ΔG°) = 1.4 kcal mol−1 is measured for two substrates differing only in the (E)/(Z)‐configuration at their double bond (see Table 2). A comprehensive force‐field molecular‐modeling study suggests that only the (E)‐derivative possesses the correct geometry for a ditopic four‐fold H‐bonding interaction between its two COOH residues and the two CONH(py) groups in 2 (Fig. 5). With N,N′‐bis [(benzyloxy)carbonyl]‐L‐cystine, the formation of diastereoisomeric complexes with (PM)‐2 is observed (Fig. 7).
Synthesis and Chiroptical Properties of Dimethyl 8,12‐Diphenylbenzo[d]heptalene‐6,7‐dicarboxylate
Authors: Rippert Andreas J. , Hansen Hans‐Jürgen 
Published: December 2004

Abstract6,10‐Diphenylbenz[a]azulene (3) was reacted with dimethyl acetylenedicarboxylate (ADM) in the presence of 2 mol‐% of [RuH2(PPh3)4] in MeCN at 100° to yield a 7:1 mixture of dimethyl 2,6‐diphenyl‐9,10‐benzotricyclo[6.2.2.01,7]dodeca‐2,4,6,9,11‐pentaene‐11,12‐dicarboxylate (4) and dimethyl 8,12‐diphenylbenzo[d]heptalene‐6,7‐dicarboxylate (5; Scheme 2). The tricycle 4, when heated in DMF at 150° for 1 h led to the formation of 81.5% of the heptalene‐6,7‐dicarboxylate 5 and 15% of the starting azulene 3. No rearrangement of tricycle 4 was observed, when it was heated at temperatures up to 180° in pseudocumene. The heptalene‐6,7‐dicarboxylate 5 was easily separated into its antipodes (PM)‐and (MP)‐5 on a Chiracel column (cf. Fig. 2). On heating at 150° for 1 h, (MP)‐5showed no racemization at all. The Ru‐catalyzed reaction of benz[a]azulene (6) with ADM led to the formation of dimethyl 9,10‐benzotricyclo[6.2.2.01,7]dodeca‐2,4,6,9,11‐pentaene‐11,12‐dicarboxylate (7; Scheme 3). However, the formation of the corresponding heptalene‐6,7‐dicarboxylate could not be observed.
Synthesis, Reactivity, and Fluxional Behaviour of [Ir2Rh2(CO)12], and Crystal Structure of [Ir2Rh2(CO)8(norbornadiene)2]
Authors: Bondietti Giacomo , Suardi Gianfranco , Ros Renzo , Roulet Raymond , Grepioni Fabrizia , Braga Dario 
Published: December 2004

AbstractThe synthesis of [Ir2Rh2(CO)12] (1) by the literature method gives a mixture 1/[IrRh3(CO)12] which cannot be separated using chromatography. The reaction of [Ir(CO)4]− with 1 mol‐equiv. of [Rh(CO)2(THF)2]+ in THF gives pure 1 in 61% yield. Crystals of 1 are highly disordered, unlike those of its derivative [Ir2Rh2(CO)5(μ2‐CO)3(norbornadiene)2] which were analysed using X‐ray diffraction. The ground‐state geometry of 1 in solution has three edge‐bridging CO's on the basal IrRh2 face of the metal tetrahedron. Time averaging of CO's takes place above 230 K. The CO site exchange of lowest activation energy is due to one synchronous change of basal face, as shown by 2D‐ and VT‐13C‐NMR. Substitution of CO by X− in 1 takes place at a Rh‐atom giving [Ir2Rh2(CO)8(μ2‐CO)3X]− (X = Br, I). Substitution by bidentate ligands gives [Ir2Rh2(CO)7(μ2‐CO)3(η4‐L)] (L = norbornadiene, cycloocta‐1,5‐diene) where the ligand L is chelating a Rh‐atom of the basal IrRh2 face. Carbonyl substitution by tridentate ligands gives [Ir2Rh2(CO)6(μ2‐CO)3(μ3‐L)] (L = 1,3,5‐trithiane, tripod) with L capping the triangular basal face of the metal tetrahedron. Carbonyl scrambling is also observed in these substituted derivatives of 1 and is mainly due to the rotation of three terminal CO's about a local C3 axis on the apical Ir‐atom.
Photoinduced Molecular Transformations. Part 142. One‐step syntheses of 1H‐benz[f]indole‐4,9‐diones and 1H‐indole‐4,7‐diones by a new regioselective photoaddition of 2‐amino‐1,4‐naphthoquinones and 2‐amino‐1,4‐benzoquinones with alkenes
Authors: Kobayashi Kazuhiro , Takeuchi Hiroyasu , Seko Shinzo , Kanno Yoshikazu , Kujime Sachiko , Suginome Hiroshi 
Published: December 2004

AbstractThe 2,3‐dihydro‐1H‐benz[f]indole‐4,9‐diones 3a–d, h were formed in a one‐step reaction in 13–82% yield by an unprecedented [3 + 2] regioselective photoaddition of 2‐amino‐1,4‐naphthoquinone (1) with various electronrich alkenes 2 (Scheme 1, Table). The [3 + 2] photoadducts derived from 1 with vinyl ethers and vinyl acetate gave 1H‐benz[f]indole‐4,9‐diones 4e, f, i, in 33–72% yield, by spontaneous loss of the corresponding alcohol or AcOH from the resulting adducts; 4i has a kinamycin skeleton. The [3 + 2] photoaddition also took place on irradiation of the differently substituted amino‐1,4‐benzoquinones 6, 7, and 12 and excess alkenes 2 in benzene, giving 1H‐indole‐4,7‐dione derivatives 13 and 14 (Scheme 3), 15a and 16 (Scheme 4), and 18 (Scheme 4), respectively. The initial products in these photoadditions were proved to be hydroquinones, the air oxidation of which yielded the heterocyclic quinones; 2,3‐dihydro‐2‐methoxy‐2‐methyl‐5‐phenyl‐1H‐indole‐1,4,7‐triyl triacetate (19) was isolated after treatment of the crude photoaddition mixture obtained from 2‐amino‐5‐phenyl‐1,4‐benzoquinone (7) and 2‐methoxyprop‐1‐ene (2f) with Ac2O and pyridine under N2. A pathway leading to the annelated hydroquinones involving ionic intermediates arising from an electron transfer in these photoadditions is proposed (Scheme 5).
Breakdown of Chlorophyll: A Tetrapyrrolic Chlorophyll Catabolite from Senescent Rape Leaves. Preliminary communication
Authors: Mühlecker Walter , Kräutler Bernhard , Ginsburg Samuel , Matile Philippe 
Published: December 2004

AbstractThe experiments leading to the isolation and to the elucidation of the constitution of Bn‐NCC‐1, a colourless non‐fluorescent chlorophyll catabolite from senescent cotyledons of rape (Brassica napus L.), are described. A series of fast‐atom‐bombardment (FAB) mass and 1H‐ and 13C‐NMR spectral experiments are used to determine the constitution of the catabolite Bn‐NCC‐1. The structural information available indicates Bn‐NCC‐1 to be a 1‐formyl‐19‐oxobilane, structurally related to ‘RP 14’, isolated earlier from artificially aged primary leaves of barley. The major differences between the constitution of the metal‐free chlorophyll pheophorbide a and that of Bn‐NCC‐1 concern oxygenolytic opening of the porphinoid macrocycle at C(4)C(5), saturation at the other meso positions, hydrolysis of the methyl‐ester function, and functionalization by a malonic‐acid unit of the side chain at C(8). This work provides for the first time the structural data of a chlorophyll‐degradation product from senescent plant leaves formed under normal growth conditions.
Nucleotides. Part XLI. The 2‐dansylethoxycarbonyl (  2‐{[5‐(dimethylamino)naphthalen‐1‐yl]sulfonyl}ethoxycarbonyl; dnseoc) group for protection of the 5′‐hydroxy function in oligodeoxyribonucleotide synthesis
Authors: Bergmann Frank , Pfleiderer Wolfgang 
Published: December 2004

AbstractUse of the 2‐dansylethoxycarbonyl (  2‐{[5‐(dimethylamino)naphthalen‐1‐yl]sulfonyl}ethoxycarbonyl; Dnseoc) group as an intermediate 5′‐OH protecting group in oligodeoxyribonucleotide synthesis using the automated phosphoramidite approach is described in a model study to an alternative strategy in RNA synthesis.