bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Non‐planarity in the Radical Anions of Tribenzo[a,c,e]cyclooctenes
Authors: Felder Patrick , Gerson Fabian , Gescheidt Georg , Heckendorn René , Tong Tat‐Hung , Wang Xiao‐Min , Wong Henry N. C. , Hou Xue‐Long
Published: December 2004

Reduction of tribenzo[a,c,e]cyclooctene (2) and its 2,3‐ and 1,4‐dimethyl derivatives (4 and 5), as well as of 1,1‐dimethyl‐10,11‐propane‐2,2‐diylidene‐1H‐benzo[5,6]cycloocta[1,2,3,4‐def]fluorene (6) and its 5,6‐didehydro derivative (7) was followed by cyclic voltammetry. The radical anions of these compounds and those of their derivatives (D)2, (D)5, and (D)6, deuteratsd at C(9) in 1 and 5 or in the corresponding position of 6, have been characterized with the use of ESR, ENDOR, and TRIPLE‐resonance spectroscopy. The cyclic‐voltammetric and proton‐hyperfine data are consistent with the increasing deviations of the radical anions from planarity in the order These deviations, due to steric or interferences in the peri‐positions 1↔14 and 4↔5, are removed in and by the introduction of bridging groups. The non‐plalarity affects the thermodynamic and kinetic stabilities of the radical anions and causes a shift in the π‐spin distribution away from that benzene ring which is linked to the two others by the essential single bonds C(4a)C(4b) and C(14a)C(14b). This finding suggests that the steric hindrance in , and is alleviated by twisting this ring out of coplanarity with the remaining (Z)‐stilbene‐like π‐system.
Synthese von N1,4‐Di(p‐cumaroyl)spermin, einem möglichen Biogenese‐Vorläufer von Aphelandrin
Authors: Veznik Frantisek , Guggisberg Armin , Hesse Manfred
Published: December 2004

Synthesis of N1,4‐Di(p‐coiimaroyl)spermine, a Possible Biogenetic Precursor of Aphelandrine

Coupling of two differently substituted 1,3‐diaminopropane units 5 and 6 (Schemes 1 and 2) lead to the key intermediate 8, a tetra‐N‐protected spermine derivative. By selective deprotection and alkylation with (E)‐4‐(mesyloxy)cinnamoyl chloride, followed by deprotection, 8 was transformed to the target spermine derivative 19. By an alternative route, the 1,3‐diaminopiopanes 10 and 11 were combined to the tri‐N‐protected tetraamine 12. The intermediates 8 and 12 can be used for the preparation of polyamine derivatives.
Synthesis, Isolation, and Full Spectroscopic Characterization of Eleven (Z)‐Isomers of (3R,3′R)‐Zeaxanthin
Authors: Englert Gerhard , Noack Klaus , Broger Emil A. , Glinz Ernst , Vecchi Max , Zell Reinhard
Published: December 2004

Developmental efforts to improve the yield of the chemical synthesis of (3R,3′R)‐zeaxanthin resulted in the isolation, partly by chromatography from reaction mixtures, and full spectroscopic characterization by 1H‐NMR, UV/VIS, and CD spectrosocpy of eleven (Z/E)‐isomers of zeaxanthin: (7Z)‐, (9Z), (13Z)‐, (15Z)‐, (7Z,7′Z)‐, (9Z,9′Z)‐ (7Z,9Z,7Z)‐, (7Z,11Z,7′Z)‐, (9Z,13Z,9′Z)‐, (7Z,9Z,7′Z,9′Z)‐, and (7Z,9Z,11Z,7′Z,9′Z)‐zeaxanthin. Five of these isomers were obtained by specific synthesis, namely the (7Z)‐, (7Z,7′Z)‐, (9Z,9′Z)‐, (7Z,9Z,7′Z)‐, and (7Z,9Z,7′Z‐9Z)‐isomers.
3′‐Substituted and 2′,3′‐Unsaturated 7‐Deazaguanine 2′,3′‐Dideoxynucleosides: Syntheses and Inhibition of HIV‐1 Reverse Transcriptase
Authors: Seela Frank , Muth Heinz‐Peter
Published: December 2004

The syntheses of 2′,3′‐dideoxy‐2′,3′‐didehydro‐β‐D‐ribofuranoside 1 and 2′,3′‐dideoxy‐3′‐fluoro‐β‐D‐ribo‐furanoside 5 of 7‐deazaguanine as well as 7‐deaza‐2′‐deoxyxyloguanosine (3) are described. The corresponding 2,4‐diamino compounds 2 and 4 were also prepared. Thus, silytation of 2‐amino‐4‐chloro‐7‐(2‐deoxy‐β‐D‐erythro‐pentofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine (6) afforded 7, which gave the oxo‐nucleoside 13 after oxidation with CrO3. NaBH4 reduction yielded 14 which, upon deprotection (Bu4NF) and nucieophific displacement, afforded 3 and 4. On the other hand, the N2‐formyl derivative of 7 was mesylated (→ 10), treated with Bu4NF, and deprotected with NH3 yielding the 2′,3′‐dideoxy‐2′,3′‐didehydro‐nucleoside 12, Nucleophilic displacement reactions on 12 yielded 1 and 2. The fluoro‐nucleoside 5 was obtained from 14 after methoxytritylation of the NH2 group (→ 16), fluorination with DAST (→ 17), and treatment with 2M NaOH. The 5′‐triphosphates of 5 and other pyrrolo[2,3‐d]pyrimidine 2′,3′‐dideoxy‐3′‐fluoro‐nucleosides were found to be highly active inhibitors of HIV‐1. reverse transcriptase, similar to those of 1 and 2.
IR, Multinuclear‐NMR, and Structural Studies on [WH(CO)2(NO)(PR3)2]: cis‐Influence of Phosphorus Ligands on Hydride Character
Authors: Van Der Zeijden Adolphus A. H. , Sontag Christoph , William Bosch H. , Shklover Valery , Berke Heinz , Nanz Daniel , Philipsborn Wolfgang Von
Published: December 2004

A thorough IR and 1H‐, 13C‐, 31P‐, 183W‐NMR spectroscopic, and X‐ray structural study was carried out on complexes of the type trans, trans‐[WH(CO)2(NO)(PR3)2], (R = Et, Me, Ph, i‐PrO, MeO, and PhO). Linear correlations could be found between Tolman's parameter X and v(CO), v(WH), v(NO), δ(13C) (CO), as well as 1n(k), k being the H/D exchange rate constant for the hydride in CD3OD. The 1J(183W,31P), 2J(31P,1H), and 2J(31P,13C) as well as the 1J(183W,1H) values are related to the electronegativity of the R groups on the phosphorus ligands. This is also indicated by EHT calculations of s‐orbital populations of appropiate W model complexes. The X‐ray structures of [WH(CO)2(NO)(PR3)2] (R = Me, Ph, and MeO) were determined. Minor differences were observed in the WP bond lenghts and in the PWP and CWC angles. No obvious relationship between X‐ray data and spectroscopic parameters could be found. All three structures reveal a bending of both the CO and PR3 ligands towards the hydride atom. The total octahedral distortion is remarkably constant (25.6, 29.4, and 27.0° tilt, respectively), although the ligands individually are very different. This is attributed to redistribution of π‐electron density between CO and PR3 groups toward the central W‐atom in the three complexes.
Einelektronen‐Redox‐Reaktionen von Octamethyl[4]radialen: Nachweis der Alternanz geradzahliger Radialene
Authors: Bock Hans , Rohn Günther
Published: December 2004

One‐Electron Redox Reactions of Octamethyl[4]radialene: Proof of the Alternancy of Even‐Membered Radialenes

The photoelectron spectrum of octamethyl[4]radialene ( = tetrakis(dimethylmethylidene)cyclobutane) yields the rather low first vertical ionization of only 7.30 eV and, therefore, the molecule can be oxidized by AlCl3/CH2Cl2 to its radical cation. The ESR and ENDOR signal patterns recorded are almost identical with those of the radical anion, generated in a [2.2.2]cryptand THF solution by reduction at a potassium metal mirror. Their near congruency is in accord with the alternant π molecular properties of even‐membered radialenes as predicted by HMO theory, and larger changes of the D2d structure of C8(CH3)8 during the redox reactions are presumably hindered by the steric overcrowding in persubstituted [4]radialenes.
Alternative Strategies for the Fmoc Solid‐Phase Synthesis of O4‐Phospho‐L‐tyrosine‐Containing Peptides
Authors: Kitas Eric A. , Knorr Reinhard , Trzeciak Arnold , Bannwarth Willi
Published: December 2004

A number of biologically relevant O4‐phospho‐L‐tyrosine‐containing peptides have been synthesized by either the global phosphorylation of the side‐chain‐unprotected L‐tyrosine moiety in presynthesized resin‐bound peptides or alternatively by the incorporation of suitably protected O4‐phospho‐L‐tyrosine building blocks in the continuous‐flow method of Fmoc solid‐phase peptide synthesis. Different phosphate‐protecting groups have been applied.
Stereoselektive Synthese von Pyrrolizidin‐Alkaloiden aus Nitroalkanonen
Authors: Janowitz Agnes , Vavrecka Mojmir , Hesse Manfred
Published: December 2004

Stereoselective Synthesis von Pyrrolizidin Alkaloids from Nitroalkanones

Reduction of 5‐nitropentadecane‐2,8‐dione (11), synthesized by a Michael reaction from nitromethane, methyl vinyl ketone, and dec‐1‐en‐3‐one, gave, depending on the conditions, two epimeric 3‐heptyl‐2,3,5,6,7,7a‐hexahydro‐5‐methyl‐1H‐pyrrolizines as the main products: Catalytic hydrogenation (Pd/C) afforded the expected 7aα‐hydro epimer 1b with cis‐orieted H‐atoms at C(3), C(5), and C(7a). NaBH3CN/NH4OAc reduction of the nitrodione 11 yielded all four diastereoisomers with the 7aβ‐hydro epimer 1a as the predominant component; 1a is a pheromone of the cryptic thief ant Solenopsis sp. The N‐atom of the pyrrolizidine ring stems from NH4OAc exclusively as shown by reduction of 11 with NaBH3CN/(15N)H4OAc.
Synthesis of Aristotelia‐type alkaloids. Part IX. Synthesis of (±)‐alloaristoteline
Authors: Güller Rolf , Borschberg Hans‐Jürg
Published: December 2004

The probably most straightforward plan to synthesize the indole alkaloid alloaristoteline (5) failed, because– in marked contrast to the regular Aristotelia series‐electrophilic reagents attack with preference C(3) of the indole moiety in the key intermediate allohobartine ((−)‐12), instead of C(18). The only product that could be isolated when (−)‐12 was treated with mineral acid was isomer (+)‐15 of 5 (Scheme 2). As a consequence, the crucial electrophilic site at C(17) was created by taking recourse to the preparation of the stabilized allylic cation VI. Gratifyingly, this alleged intermediate, obtained from precursor (±)‐18, cyclized smoothly to protected (±)‐18,19‐didehydroalloaristoteline (±)‐17, which was transformed in two high‐yield steps into the racemic form of the target molecule 5 (Scheme 4). This successful alternative provides unambiguous evidence that the recently revised structure of 5 is indeed correct.
Dependence of the Regioselectivity of Photo‐oxidative Ring Opening of the Chlorophyll Macrocycle on the Complexed Metal Ion
Authors: Iturraspe José , Gossauer Albert
Published: December 2004

On irradiation with visible light in the presence of air, the zinc complex 1b of pyropheophorbide‐a methyl ester (1a) is photo‐oxidized at the C(20) methine bridge yielding the corresponding 19‐formyl‐21H‐bilin‐1(23H)‐one derivative 2. Surprisingly, the cadmium complex Ic is cleaved, under the same conditions, at the C(5) methine bridge affording the same type of bilinone which has been recently characterized as an early product of chlorophyll catabolism in plants.
Metal π‐complexes of benzene derivatives. Part. 38. Pentaphenyltriphosphane(5) as a chelating η12‐ligand. Unusual formation of an interannular –(PPh)3–bridge at bis(benzene)chromium
Authors: Elschenbroich Christoph , Sebbach Jochen , Metz Bernhard
Published: December 2004

[(l‐6):(1′‐6′)‐η‐Pentaphenyltriphosphane(5)]chromium (8), which is formed from bis(lithio‐η6‐benzene)‐chromium and dichlorophenylphosphane, and which is prepared more rationally from bis(chloro‐η6‐benzene)‐chromium and K2P3Ph3, is the first sandwich complex featuring an interannular oligophosphane bridge –(PPh)n‐, n ≥ 2; 31P{1H}‐ and 1H‐NMR spectra suggest that the stereoisomer 8‐meso1 is formed exclusively and that the –(PPh)3‐ link in this triphospha[3]chromocyclophane is non‐fluxional in the range 193 < T < 348 K.
A Convenient Synthesis of Vinyl Sulfides
Authors: Katritzky Alan R. , Afridi Amir S. , Kuzmierkiewicz Wojciech
Published: December 2004

tert‐Alkyl sulfides, with an α‐(1H‐benzotriazol‐1‐yl) group 6 and 13, are readily prepared from N‐[(aryl‐thio)methyl]‐1H‐benzotriazoles 3 and N‐(11), respectively, by reaction with BuLi and then with the appropriate electrophile. The tert‐alkyl sulfides 6 and 13 are smoothly converted by BF3. OEt2 into vinyl sulfides 5, 7 or 12, respectively, in satisfactory yields.
Isomerization of N‐[α‐(Alkylthio)alkyl]‐ and N‐[α‐(Arylthio)alkyl]benzotriazoles
Authors: Katritzky Alan R. , Kuzmierkiewic Wojciech , Perumal Subbu
Published: December 2004

The thermal isomerizations of N‐[α‐(alkylthio)alkyl]‐ and N‐[α‐(arylthio)alkyl]benzotriazoles have been investigated under N2 atmospheres (i) in toluene, xylene, MeOH, or EtOH, in the presence of acid catalysts and (ii) in the absence of solvent. The sulfide isomerization rates depend on the number of H‐atoms carried by the C‐atom attached to the N‐atom of the benzotriazole: tertiary (no hydrogen) > secondary (1 hydrogen) > primary (2 hydrogens). The results support an isomenzation mechanism involving a heterolytic NC bond cleavage with formation of sulfonium/carbonium and benzotriazolate ions.
Structure Determination of New Iridals from Iris pallida and Iris foetidissima
Authors: Littek Andrè , Marner Franz‐Josef
Published: December 2004

The four novel iridals 8–10 and 18 were isolated from rhizome extracts of Iris pallida and Iris foetidissima, and their structures were established by spectroscopic methods and oxidative degradation. The compounds 8–10 bearing a conjugated triene moiety are extremely labile and decompose rapidly. Thus, the monocyclic triene 8 was only isolated after its conversion to a Diels‐Alder adduct with 4‐phenyl‐3H‐1,2,4‐triazole‐3,5(4H)‐dione (14), The tricyclic iridal 18 is a hitherto unknown precursor of α‐irone. The possible biogenesis of these unusual triterpenoids is discussed.
Synthesis of a Glucose‐Derived Tetrazole as a New β‐Glucosidase Inhibitor. A New Synthesis of 1‐Deoxynojirimycin
Authors: Ermert Philipp , Vasella Andrea
Published: December 2004

The tetrazole 1 is a new β‐glucosidase inhibitor (IC50=8·10−5 M, Emulsin), obtained (92%) by deprotection of 22, the product of an intramolecular cycloaddition of the azidonitrile 20. This azidonitrile was formed as an intermediate by treating the L‐ido‐bromide 14 or the L‐ido‐tosylate 19 with NaN3 at 110–120°. It was isolated in a separate experiment. The yield of 22 from 19 reached 70%; 21 was formed as by‐product (10%). The bromide 14 (42%) and the iodide 15 (30–35%) were obtained from the nitrile 13, together with the 2,5‐anhydro‐L‐idononitrile 16, which was formed in ca. 35–45%. The tosylate 19 was obtained from 18 (97%). To obtain 18, the nitrile 13 was oxidized according to Swern (→17, 92%) and then reduced (NaBH4, CeCl3), leading to 18and 13 (92%, 18/13 93:7). Reduction of the tetrahydropyridotetrazole 22 with LiAlH4 afforded 83 % of the piperidine 23, which was deprotected to (+)‐1‐deoxynojirimycin hydroacetate (2·AcOH, 86%) and further converted into the corresponding hydrochloride and into the free base 2.
Radical Anions of Cyclic Azoalkanes: An ESR, ENDOR, and TRIPLE‐Resonance Study
Authors: Ess Caspar H. , Gerson Fabian , Adam Waldemar
Published: December 2004

Radical anions often monocyclic and bicyclic azoalkanes containing the azo group in (Z)‐conformation, have been fully characterized by their hyperfine data with the use of ESR, ENDOR, and general‐TRIPLE‐resonance spectroscopy. These azoalkanes are represented by 3,3,5,5‐tetramethyl‐1‐pyrazoline (1), 2,3‐diaza‐bicyclo[2.2.1]hept‐2‐ene (4), and 2,3‐diazabicyclo[2.2.2]oct‐2‐ene (9), as well as by their derivatives 2,3, 5–8, and 10. For all radical anions 1″–10″, the 14N‐coupling constant, aN, is in the range of +0. 83 to +0. 97 mT; this finding indicates that the spin population is essentially restricted to the π system of the azo group. The 14N‐hyperfine anisotropy largely affects the width of ESR lines, particularly at low temperatures. Substantial coupling constants of 7Li‐, 23Na‐, 39K‐, and 133Cs‐nuclei point to a close association of the radical anions with their alkali‐metal counterions. With the exception of 39K, these nuclei give rise to readily observable ENDOR signals which appear along with those stemming from protons. The prominent hyperfine features of 1″–10″ are discussed.
Photochemical Reactions. 153th communication. Photochemistry of acylsilanes: Photolyses and thermolyses of α,β‐epoxy silyl ketones
Authors: Scheller Markus E. , Frei Bruno
Published: December 2004

The photolyses and thermolyses of the α,β‐epoxy silyl ketones 5 and 6 are described. On n,π*‐excitation, the silyl ketones 5 and 6 were transformed to the ketone 7 and the ketene 8 in quantitative yield. The formation of 8 may be explained by initial cleavage of the C(α)O bond and subsequent C(1)→C(2) migration of the (t‐Bu)Me2Si group. In contrast to the acylsilanes 5 and 6, the photolyses of the analogous methyl ketones 11 and 12 gave a very complex mixture of products. On thermolysis, 5 and 6 yielded the ketone 7 and the acetylenic compound 9, which were probably formed via a siloxycarbene intermediate. In addition, the 1,3‐dioxle 10 was formed via an initial C(α)C(β) bond cleavage leading to the ylide g and subsequent intramolecular addition of the carbonyl group. The analogous 1,3‐dioxole 13 was obtained on pyrolysis of the methyl ketones 11 and 12.
Synthesis of Enantiomeric Pure E‐Nor‐15‐azayohimbines
Authors: Valls Nativitat , Bonjoch Josep , Del Alamo Carlos , Bosch Joan
Published: December 2004

A stereodivergent synthesis of enantiomerically pure E‐nor‐15‐azayohimbines via condensation of tryptamine with derivatives of pyroglutamate 4 is reported. When the Pictet‐Spengler reaction was induced in refluxing aqueous AcOH a nearly equimolar ratio of lactams 7 and 8 was obtained, whereas under kinetic control (TFA, room temperature) the trans‐derivative 8 was the major product. In contrast, cyclization of amido acetal 12 with TsOH gave the cis‐derivative 7 as preponderant component.
Einelektronen‐Redox‐Reaktionen von Octaphenyl[4]radialen: Erzeugung und ESR/ENDOR‐Charakterisierung seines Radikal‐Anions und Radikal‐Kations
Authors: Bock Hans , Rohn Günther
Published: December 2004

One‐Electron Redox Reactions of Octaphenyl[4]radialene: Generation and ESR/ENDOR Characterisation of Its Radical Anion and Radical Cation

The cyclovoltammograms of octaphenyl[4]radialene in DMF or THF at room temperature disclose each two quasireversible reduction and oxidation potentials at −1.4 V/−1.7 V and +0.7 V/+0.9 V. Accordingly, both the radical anion and the radical cation can be generated: Ph8C by K metal mirror reduction of a [2.2.2]cryptand containing THF solution, and Ph8C by TI3⊕(⊖OOCCF3)3 oxidation in H2CCl2. Their ESR/ENDOR and General Triple spectra differ considerably in the number of resolved 1H couplings (M·⊖: 5 and M·⊕: 3) as well as in their spectral widths (M·⊖: a1H 0.090 to 0.017 mT; M·⊕: a1H 0.066 to 0.023 mT) suggesting different changes in the D2d structure of the neutral molecule on electron uptake or extrusion.
Investigations Concerning an Unexpected Reaction between the Dimsyl Anion ( = (Methylsulfinyl)methanide) and a γ,δ‐Epoxy‐ketone
Authors: Beerli René , Borschberg Hans‐Jürg
Published: December 2004

The reaction of 2,2‐dimethyl‐5‐(1,2‐epoxypropyl)cyclohexanone (7) with t‐BuOK in DMSO furnished a small amount of 5‐(1‐hydroxyprop‐2‐enyl)‐2,2‐dimethylcyclohexanone (12) and the 4 unexpected products 13–16 which contain one to three additional C‐atoms (Scheme 2). The relative configuration of the major product 1‐(4′,4′‐dimethyl‐2′,3′‐dimethylidenecyclohexyl)propane‐1,2‐diol (15) was shown to be 1RS, 2RS,1′SR via NOE measurements performed on a derivative thereof. A crossover experiment in DMSO/[13C2]DMSO 1:1 as solvent showed that the two additional C‐atoms of this product originate from a single molecule of DMSO (Scheme 5). A tentative mechanistic scheme, consistent with all experimental observations, is proposed which involves a [2,3]‐sigmatropic rearrangement of an (allylsulfinyl)methanide to a sulfenic acid as one of the key steps (V → 24, Scheme 8). We corroborated part of this hypothetic scheme by taking recourse to a model compound (7‐(methylsulfinyl)‐p‐mentha‐1,8‐diene (32/33), readily prepared in two steps from perilla alcohol (30)), which reacted as predicted by the proposed mechanism (Schemes 9 and 10).
Opening of the Macrocyclic Ring in 5,10:8,9‐Disecosteroids ( = Steroklastanes)
Authors: Lorenc Ljubinka , Bondarenko‐Gheorghiu Lidija , Pavlović Vladimir , Fuhrer Hermann , Kalvoda Jaroslav , Mihailović Mihailo Lj.
Published: December 2004

Catalytic hydrogenation of the Δ3‐unsaturated (9R,10 R)‐ and (9S,10 S)‐epoxyenol lactones 3a, b., and 4a, b., respectively, affords, in addition to the expected saturated epoxylactones 5a, b and 7a, b, also open‐chain products, i.e. the diastereoisomeric (9R,10R)‐ and (9S,10S)‐9,10‐expoxy‐8‐oxo‐4,5‐secosteroklastan‐5‐oic acids 6a, b. and 8a, b. Alkaline hydrolysis of the lactone ring of compounds 5 and 7 and subsequent acetylation of the corresponding hydroxy derivatives give as the major products the open‐chain, diasteroisomeric (9R,10R)‐ and (9S,10S)‐4‐acetoxy‐9,10‐epoxy‐methyl esters 9a, b and 11a, b, respectively, and, but only in the androstane series, the tetrahydropyran derivatives 10a and 12a, as the minor components.
Epimeric Isopavine N‐Oxides from Roemeria refracta
Authors: Gözler Belkis , Ali Önür Mustafa , Bilir Serap , Hesse Manfred
Published: December 2004

Roemeria refracta DC. (Papaveraceae) of Turkish origin yielded two novel epimeric N‐oxides, (−)‐(5R, 11S,14R)‐reframidine N‐oxide ( = (−)‐(5R, 11S,14R)‐11,12‐dihydro‐14‐methyl‐11,5‐(iminomethano)‐5H ‐cyclohepta[1, 2‐f: 4, 5‐f′]bis[1,3]benzodioxole 14‐oxide; 1) and (−)‐(5R, 11S, 14S)‐reframidine N‐oxide ( = (−)‐(5R, 11S, 14S)‐11, 12‐dihydro‐14‐methyl‐11, 5‐(iminomethano)‐5H‐cyclohepta[1, 2‐f:4, 5‐f′]bis[1, 3]benzodioxole 14‐oxide; 2). The isolated (−)‐roelactamine ( = (−)‐11, 12‐dihydro‐14‐methyl‐11, 5‐(iminomethano)‐5H‐cyclohepta[1, 2‐f:4, 5‐f′]bis[1, 3]benzodioxol‐15‐one, 4) is the first natural isopavinoid incorporating a lactam group. The epimeric (−)‐15‐(2‐oxopropyl)reframidines ( = (−)‐1‐[11, 12‐dihydro‐14‐methyl‐11, 5‐(iminomethano)‐5H‐cyclohepta[1, 2‐f:4, 5‐f′]bis[1, 3]benzodioxol‐15‐y1]propan‐2‐ones; 5/6) and the epimeric (−)‐ethyl (reframidin‐15‐yl)acetates ( = (−)‐ethyl [11, 12‐dihydro‐14‐methyl‐11, 5‐(iminomethano)‐5H‐cyclohepta[1, 2‐f:4, 5‐f′]bis[1, 3]benzodioxol‐15‐y1]acetates; 7/8) are probably artifacts. (±)‐Coclaurine (9), (±)‐N‐methylcoclaurine (10), (−)‐roemeridine (11), and N‐feruloyltyramine (12) are also isolated from R. refracta together with the previously reported bases. Specific 13C‐NMR assignments are reported for the first time for the isopavines.
Quantum Yields of Singlet‐Oxygen Production by Some Natural Quinoid Fungal Metabolites and Derivatives
Authors: Aminian‐Saghafi Taraneh , Nasini Gianluca , Caronna Tullio , Braun André M. , Oliveros Esther
Published: December 2004

Perylene quinone compounds of natural and syntheitc origin have been investigated for their quantum efficiency of singlet‐oxygen production (ΦΔ). The results may be interpreted by a qualitative relation between ΦΔ and the planarity of the sensitizer molecules, highest values (0.8–0.9) being observed where planarity is favoring tautomeric structures. On the other hand, derivatives exhibiting non‐planar quinoid structures show lower ΦΔ, and methylated derivatives react photochemically.
Cuprous Complexes and Dioxygen. Part 12.. Rate law and mechanism of the copper‐catalyzed oxidation of ascorbic acid in aqueous acetonitrile
Authors: Mi Li , Zuberbühler Andreas D.
Published: December 2004

The copper‐catalyzed oxidation of ascorbic acid (AscH2) has been studied with a Clark electrode in aqueous MeCN. CuI or CuII may be equally used as the source of metal ion, without influence on the rate law. At sufficiently high [MeCN], the rate of the overall reaction is essentially given by the rate of CuI autoxidation: the reaction is of first order with respect to [Cu] and [O2] and shows an inverse‐square dependence on [MeCN] as observed for the autoxidation of Cu. The pH dependence is complicated by the combination of the intrinsic pH effect on autoxidation with an additional term in the rate law which is directly proportional to [AscH−]. The latter term is explained by direct oxidation of the organic substrate by the primary dioxygen adduct of CuI, CuO. For [MeCN] < 0.7M, a gradual and pH‐dependent transformation of this rate law and deviation from the first‐order dependence on [O2] is indicated.
Isomerization of Olefins Catalyzed by the Hexaaquaruthenium(2+) Ion. Preliminary communication
Authors: Karlen Thomas , Ludi Andreas
Published: December 2004

Isomerization of olefins, in particular the useful transformation of allyl to vinyl ethers is catalyzed by the hexaaquaruthenium(2+) ion, producing the (E)‐isomers under mild conditions.
Photochemical Synthesis and Some Reactions of 7‐Oxa‐and 7‐Thiatricyclo[3.2.1.03,6]octan‐2‐ones
Authors: Gebel Rolf‐Christoph , Margaretha Paul
Published: December 2004

Irradiation (λ = 350 nm) of newly synthesized 2‐acetyl‐ or 2‐methyl‐2‐(alk‐2‐enyl)furan‐3(2H)‐ones 1 and 2‐acetyl‐ or 2‐methyl‐2‐(prop‐2‐enyl)thiophen‐3(2H)‐ones 2 affords the corresponding 1‐acetyl‐ or 1‐methyl‐substituted 7‐oxa‐ and 7‐thiatricyclo[3.2.1.03,6]octan‐2‐ones 10 and 11, respectively, via regioselective intramolecular [2 + 2] photocycloaddition in 65–95% yield (Scheme 2). The 1‐acetyl‐substituted O‐derivatives 10b and 10c undergo ring opening on treatment with MeONa in MeOH at–78° to afford stereoselectively methyl 3‐exo‐acetyl‐2‐oxabicyclo[3.2.0]heptane‐7‐endo‐carboxylates 12b and 12c, respectively, while a 2:1 diastereoisomeric mixture of methyl 3‐acetyl‐2‐thiabicyclo[3.2.0]heptane‐7‐endo‐carboxylates 13 and 14 is obtained from the corresponding S‐derivative 11b. The outcome of the Huang‐Minlon reduction of the 1‐methyl‐substituted ketones 10a and 11a is again influenced by the heteroatom in the tricycle. While 1‐methyl‐7‐oxatricyclo[3.2.1.03,6]‐octane (15) is the only product from the corresponding oxatricyclooctanone 10a, a 1:2 mixture of 1‐methyl‐7‐thiatricyclo[3.2.1.03,6]‐octane (16) and 3‐methylbicyclo[3.1.1]hept‐2‐ene‐6‐endo‐thiol (17) is obtained from the analogous S‐compound 11a, both products stemming from a common carbanion precursor.
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

[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)‐thiones

At 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 Enlargement

Treatment 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

Naturally 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

This 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

High‐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

The 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

Cucl2‐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

Treatment 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 Salicylohydrazide

3‐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

Oxidative 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

The 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

6,10‐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

The 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

The 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

The 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.