bluuebunny/crossref_metadata_2025 huggingface dataset:
The Photoreversible Addition of Sulfur Dioxide to Benzobenzvalene: A new Approach to the Benzoprefulvene Biradical
Authors: Burger Ulrich , Gmünder Christian , Schmidlin Serge , Bernardinelli Gérald
Published: December 2004

Benzobenzvalene (naphthvalene; 1) is shown to add SO2 to a lateral bicyclobutane bond with formation of a sulfone 2 and a ‘γ‐sultine’ 3. The structure of the latter is unambiguously established by X‐ray diffraction. Both adducts extrude SO2 upon direct photolysis at 254 nm and regenerate 1 accompanied by naphthalene in a 1:3 ratio. This result is interpreted in terms of a reversible homolytic cleavage leading, for both, 2 and 3, to the same sulfinyloxy biradical 5, which by loss of SO2 gives the benzoprefulvene biradical 6. The latter in its singlet state undergoes ring closure to 1, or it opens to give naphthalene.
A Study on the Odour/Structure Relationship of Patchoulol and Norpatchoulenol
Authors: Spreitzer Helmut
Published: December 2004

In continuation of studying structure/activity relationships of odorous compounds, the influence of the bridgehead‐bonded Me group of (+)‐norpatchoulenol (1) and (−)‐patchoulol (2) and the olfactory properties of the corresponding unsaturated and saturated derivatives (±)−3, (±)−4 and (±)−5, (±)−6, respectively, are studied. The key odour descriptors‐wood, earth, and camphor‐are used for classification.
Synthesis of the 6‐C‐Methyl and 6‐C‐(Hydroxymethyl) Analogues of N‐Acetylneuraminic Acid and of N‐Acetyl‐2,3‐didehydro‐2‐deoxyneuraminic Acid
Authors: Vasella Andrea , Wyler René
Published: December 2004

The synthesis of 6‐C‐methyl‐Neu2en5Ac (4), 6‐C‐(hydroxymethyl)‐Neu2en5Ac (5), and 6‐C‐methyl‐Neu5Ac (6) is described. The 4‐methylumbellyferyl glycosides 8 and 9 were also prepared but proved unstable. Protection of the previously reported nitro ether 10 (→11) followed by a Kornblum reaction gave the branched‐chain derivative 13 which was transformed into aldehyde 14 and hence via 16 into the‐protected 6‐C‐hydroxymethylated 20 and into the 6‐C‐methyl‐substituted 18 (Scheme 1). Debenzylidenation of 20 and 18 afforded the diols 21 and 19, respectively. Selective oxydation of 19 followed by esterification (→ 22), acetylation (→ 23), and elimination led to the protected 6‐C‐methyl‐Neu2en5Ac derivative 24 (Scheme 2). Bromomethoxylation yielded mainly 25 and some 26, which were reductively debrominated to 27 and 28, respectively. Attempted deprotection of 27 did not lead to the corresponding acid, but to the 2,7‐ and 2,8‐anhydro compounds 29 and 30 which were characterised as their peracetylated esters 31 and 32 (Scheme 3). The structure of 32 was established by X‐ray analysis. Oxydation of 19 and 21, followed by deprotection, esterification, and acetylation gave 37 and 38, respectively (Scheme 4). The branched‐chain Neu2en5Ac derivatives 4 and 5 were obtained by β‐elimination (→ 39 and 40) and deprotection. Omission of the esterification after oxydation of 33 and 34 gave the lactones 35 and 36 which were transformed into 37 and 38, respectively. Bromoacetoxylation of 39 gave 41‐43 which were reductively debrominated to 44 (from 41 and 42) and 45 (Scheme 5). Bromoacetoxylation of 40 yielded 46 which was debrominated to 47. Glycosidation of the glycosyl chlorides obtained from 44 and 47 led to the α ‐D‐glycosides 48 and 49 and to the elimination products 39 and 40, respectively (Scheme 6). Transesterification of 48, followed by saponification gave the unstable glycoside 8 and hence 6‐C‐methyl‐Neu5Ac (6). The unstable glycoside 9 was obtained by similar treatment of 49 but yielded 50 under acidic conditions. The branched‐chain 4 and 5 were weak inhibitors of Vibrio cholera sialidase, and 8 and 9 were very poor substrates.
Microbial Metabolism of the Diterpene Sclareol: Oxidation of the A Ring by Septomyxa affinis
Authors: Kouzi Samir A. , McChesney James D.
Published: December 2004

Microbial metabolism of the diterpene sclareol (1) was studied. Screening studies have shown a number of microorganisms capable of metabolizing 1. Preparative‐scale fermentation with Septomyxa affinis ATCC 6737 has resulted in the production of three fungal metabolites that have been characterized by 2D‐NMR techniques and chemical reactions. These metabolites have been identified as 8α,13β‐dihydroxylabd‐14‐en‐3‐one (2), labd‐14‐ene‐3β.8α,13β‐triol (4), and labd‐14‐ene‐2α,8α,13β‐triol (6).
The Solid‐State and Solution Conformations of (+)‐Chelidonine
Authors: Kamigauchi Miyoko , Miyamoto Yuko , Iwasa Kinuko , Sugiura Makiko , Nishijo Zjujiro , Takao Narao , Ishida Toshimasa , In Yasuko , Inoue Masatoshi
Published: December 2004

The solid‐state and solution conformations of (+)‐chelidonine (1), a biologically active alkaloid, were determined by X‐ray diffraction and 1H‐NMR spectroscopy, X‐Ray diffraction analysis revealed a conformer with B/C ‘anti‐type’ cis conjunction, a half‐chair of ring B, and a twist half‐chair of ring C. One H2O molecule per one alkaloid molecule was cocrystallized and stabilized by H‐bonding with OHC(11). Analysis of the thermal behavior of the crystal showed more thermal stability in the monohydrate than the anhydrate. The NMR measurement of concentration and temperature dependences in CDCl3 and in (CD3)2SO suggested that the OH group of 1 was intramolecularly H‐bonded to N(5) in (CD3)2SO and intermolecularly H‐bonded to the solvent in CDCl3. Conformational‐energy calculations by the MNDO method showed that the intramolecular H‐bond was little affected by the conformational stabilization of 1.
Influence of the Axial Alkyl Ligand on the Reduction Potential of Alkylcob(III)alamins and Alkylcob(III)yrinates
Authors: Zhou De‐Ling , Tinembart Olivier , Scheffold Rolf , Walder Lorenz
Published: December 2004

The irreversible‐reduction potentials of 26 alkylcob(III)alamins (RCblIII 1a–z) and 26 alkylcob(III)yrinates (R‘Cby’III; 2a–z) (Ep 1a–z and Ep 2a–z, resp.) have been measured in situ by single‐scan voltammetry of hydroxocob(III)alamin hydrochloride (vitamin B12b‐ HCl; 1) or heptamethyl cob(II)yrinate perchlorate (ClO4‘Cby’II; 2) in presence of the corresponding alkyl halides (RX;3a–z) in DMF. The reduction potentials of alkylcobalt complexes exhibiting half‐life times as short as a few seconds become measurable by this technique. Thermodynamic cycles prove that the observed reduction potentials are closely related to the standard reduction potentials E°(RCoIII + e−⇆R⋅ + CoI). Electron‐withdrawing groups and/or an increased degree of substitution at the Co‐bound C‐atom in RCblIII and, R‘Cby’III shift Ep(1a–z) and Ep (2a–z) towards positive potentials. Linear correlations have been found between Ep(1a–z) (Ep(2a–z)) of RCblIII (R‘Cby’III) and the pKa of RH (or the Taft σ*‐ or the Hammett σ‐values of R) within each class of R, i. e. MeCblIII (Me‘Cby’III), primary RCblIII (R‘Cby’III) and secondary RCblIII (R‘Cby’III). The correlations allow to distinguish between electronic effects of the Co‐bound alkyl residues and their steric interactions with the corrin side chains. The correlations have further been used to visualize the light‐induced formal insertion of an olefin into the Co, C‐bond of an alkylcobalamin (Scheme 2, 1a→1u), a key step in the vitamin‐B12‐catalized C, C‐bond formation.
The Coordination Chemistry of 1,2‐Bis[(diphenylphosphino)methyl]benzene with Nickel(II), Palladium(II), Platinum(II), and Platinum(0) and the X‐Ray Crystals Structure of [Pt{1,2‐bis[(diphenylphospino)methyl]benzene}(C2H4)]
Authors: Camalli Mercedes , Caruso Francesco , Chaloupka Stanislav , Leber Ernest M. , Rimml Heinrich , Venanzi Luigi M.
Published: December 2004

The preparation of complexes [MX2(1)] (M = Ni, Pd, and Pi; X ‐ Cl, Br, and I; 1 = 1,2‐bis[(diphenylphosphino)methyl]benzene). [Pt(OSO2CH3)Et(1)], [Pt(alkene)(1)] (alkene ‐ C2H2, and CH2 = CHCN), and [(1)Pt‐(μ‐H)2PtH(1)][BPh4] is reported. Their 1H‐ and 31P‐NMR spectra were recorded and used lor structural assignments. The X‐ray crystal structure of [Pt(C2H4)(1)] was determined. It is shown that the PPtP bond angle in this complex differs significantly from those found in related compounds with monodentate phosphines, and that this difference is likely to be due to intramolecular contacts.
Umsetzungen von 3‐(Dimethylamino)‐2,2‐dimethyl‐2H‐azirin mit Barbitursäure‐Derivaten
Authors: Schläpfer‐Dähler Marlise , Heimgartner Heinz
Published: December 2004

Reactions of 3‐(Dimethylamino)‐2,2‐dimethyl‐2H‐azirines with Barbituric‐Acid Derivatives

The reaction of 3‐(dimethylamino)‐2,2‐dimethyl‐2H‐azirine (1) and 5,5‐disubstituted barbituric acids 5 in i‐PrOH at ca. 70° gives 2‐[5‐(dimethylamino)‐4,4‐dimethyl‐4H‐imidazol‐2‐yl]alkanamides of type 6 in good yields (Scheme 1). The formation of 6 proceeds with loss of CO2; various reaction mechanisms with a zwitterionic 1:1 adduct B as common intermediate are discussed (Schemes 2 and 5). Thermolysis of product 6 leads to 2‐alkyl‐5‐(dimethylamino)‐4,4‐dimethyl‐4H‐imidazoles 8 or the tautomeric 2‐alkylidene derivatives 8′ via elimination of HNCO (Scheme 3). The latter undergoes trimerization to give 1,3,5‐triazine‐2,4,6‐trione. No reaction is observed with 1,5,5‐trisubstituted barbiturates and 1 in refluxing i‐PrOH, but an N‐alkylation of the barbiturate occurs in the presence of morpholine (Scheme 4). This astonishing reaction is explained by a mechanism via formation of the 2‐alkoxy‐2‐(dimethylamino )aziridinium ion H which undergoes ring opening to give the O‐alkylated 2‐amino‐N1,N1‐dimethylisobutyramide I as alkylating reagent (Scheme 4).
Eine neue 1,3‐Oxathiolan‐Synthese: Spirocyclische 1,3‐Oxathiolane aus der Lewis‐Säure katalysierten Umsetzung von 1,3‐Thiazol‐5(4H)‐thionen mil Oxiranen
Authors: Tromm Peter‐Claus , Heimgartner Heinz
Published: December 2004

A New 1,3‐Oxathiolane Synthesis: Spirocyclic 1,3‐Oxathiolanes from the Lewis‐Acid‐Catalyzed Reaction of 1,3‐Thiazole‐5(4H)‐thiones and Oxiranes

The BF3·Et2O‐catalyzed reaction of 2,4,4‐trisubstituted 1,3‐thiazole‐5(4H)‐thiones 13 with alkyl‐ and phenyl‐substituted oxiranes 7 in CH2Cl2 at room temperature leads, in very good yields, to 1‐oxa‐4,6‐dithia‐8‐azaspiro[4.4]non‐7‐enes 14 and 15.
Nucleotides. Part XXXIVSynthesis of Modified Oligomeric 2′–5′A Analogues: Potential Antiviral Agents
Authors: Herdewijn Piet , Ruf Klaus , Pfleiderer Wolfgang
Published: December 2004

A series of new 2′–5′‐oligonucleotide trimers carrying a 9‐(2′,3′‐anhydro‐β‐D‐ribofuranosyl)‐(59), 9‐(3′‐deoxy‐β‐D‐glycero‐pent‐3‐enofuranosyl)‐(63), 9‐(3′‐azido‐3′‐deoxy‐β‐D‐xylofuranosyl)‐(62), and 9‐(3′‐halo‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine (60 and 61) moiety at the 2′‐terminal end have been synthesized via the phosphotriester method. The properly protected, modified monomeric building blocks (6, 9, 16, 19, 27, 33, 36, 37, and 43) were obtained, in general, by a sequence of reactions, introducing the protecting groups into the right positions. Their condensations with the intermediary dimeric 2′‐terminal phosphodiesters 48 and 49 led to the fully protected 2′–5′‐trimers 50–58 which were deblocked to form the free 2′–5′‐trimers 59–63. Easy elimination of HBr on deprotection did not allow to form the trimeric (3′‐bromo‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine analogue but only 63 carrying an unsaturated sugar moiety instead. The newly synthesized compounds have been characterized by UV and NMR spectra as well as by elemental analysis.
Neurotoxic Sesquiterpenoids from the Yellow Star Thistle Centaurea solstitialis L. (Asteraceae)
Authors: Wang Ying , Hamburger Matthias , Cheng Celine H. K. , Costall Brenda , Naylor Robert J. , Jenner Peter , Hostettmann Kurt
Published: December 2004

Ingestion of yellow star thistle (Centaurea solstitialis L.) by horses produces parkinsonism due to nigro‐pallidal degeneration. The toxin responsible has not been identified so far. A CH2Cl2 extract from the aerial parts of C. solstitialis exhibited significant neurotoxicity against primary neuronal cultures of foetal rat brain. Activity‐guided fractionation yielded the known sesquiterpene lactones solstitialin A (1), 13‐0‐acetylsolstitialin A (3), cynaropicrin (4), and the hitherto unknown 3‐O‐acetylsolstitialin A (2). In the bioassay with rat foetal full cell culture, 3 and 4 were toxic in a concentration‐dependent manner and may be responsible for the ability of the plant to cause neurodegenerative changes in the brain of horses.
Magnetic‐Field Effect in Aromatic Dediazoniation
Authors: Laali Kenneth K. , Gao Hong
Published: December 2004

Homolytic dediazoniation of tribromo‐ and trichloro‐benzenediazonium tetrafluoroborates in highly ionizing, low‐nucleophilicity solvents (trifluoroethanol and trifluoromethanesulfonic acid (TfOH)) exhibits a strong magnetic‐field dependency of dediazoniation products; a more facile singlet‐to‐triplet intersystem crossing results in increased radical‐escape products at higher magnetic fields.
Enantioselective Synthesis of Both Enantiomers of a Isoproterenol Analogue and of Di‐O‐pivaloylepinephrine
Authors: Solladié‐Cavallo Arlette , Simon‐Wermeister Marie‐Claude , Farkhani Dariouch
Published: December 2004

An asymmetric synthesis of the analogue 4a of isoproterenol and of di‐o‐pyvaloylepinephrine 3 which provides both enantiomers in optically pure state is reported. The key step of the method is the highly diastereo‐selective reduction (using DIBAL or DIBAL/ZnCl2) of a β‐ketosulfoxide 7 which leads, as desired, to the (S)‐ or the (R)‐configuration at C(1) (Schemes 4 and 5).
A New Synthesis of (2S,3R,4R)‐2‐(Hydroxymethyl)pyrrolidine‐3,4‐diol
Authors: Meng Qingchang , Hesse Manfred
Published: December 2004

The title compound 6 was synthesized from 2,3,5‐tri‐O‐benzyl‐D‐arabinofuranose (7) in three steps and 48% overall yield. Moreover, it was shown, in the case of γ‐hydroxy amide 9, that the Mitsunobu reaction is not suitable for the preparation of γ‐lactams, because O‐alkylation is predominant.
Biosynthesis of the Spermine Alkaloid Aphelandrine
Authors: Papazoglou Georgios , Sierra Jorge , Homberger Katharina , Guggisberg Armin , Woggon Wolf‐Dietrich , Hesse Manfred
Published: December 2004

Aphelandrine (1) is shown to be biosynthesized in the root cells of Aphelandra tetragona (VAHL) NEES from labelled putrescine (4), spermidine (5), and cinnamic acid (3). Whether spermine (6) and the (p‐hydroxycinnamoyl)spermidine 8 are precursors of 1 is uncertain, since the latter is hydrolysed to a large extent before incorporation, and the former is metabolized to 4 and 5. Methionine (7) is the source of the 3‐aminopropyl unit of 5 and 6.
Ionization Behavior and Ionization‐Dependent Conformation of Raclopride, a Dopamine D2 Receptor Antagonist
Authors: Carrupt Pierre‐Alain , Tsai Ruey‐Shiuan , Tayar Nabil El , Testa Bernard , de Paulis Tomas , Högberg Thomas
Published: December 2004

Raclopride, an antipsychotic 6‐methoxysalicylamide (= 2‐hydroxy‐6‐methoxybenzamide) derivative, was shown by titrimetry and UV‐pholometry to exist in zwitterionic form at physiological pH. Calculations revealed that the neutral and zwitterionic forms differ considerably in their conformational behavior, the latter form being energetically favored by an intramolecular phenolate–ammonium ionic bond. These findings indicate that raciopride and other halogenated 6‐melhoxysalicylamides with a highly acidic phenolic group may not resemble other ortho‐methoxybenzamides in their stereoelectronic structure and mode of binding to the dopamine D2 receptor.
The Lewis basicity of the [Pt3(μ‐CO)3(PR3)3] clusters and the X‐ray crystal structure of [{ZnI2}{Pt3(μ‐CO)3(PPh(i‐Pr)2)3}]
Authors: Stockhammer Andreas , Dahmen Klaus‐Hermann , Gerfin Tobias , Venanzi Luigi M. , Gramlich Volker , Fetter Walter
Published: December 2004

The cluster compounds [Pt3(μ‐CO)3(PR3)3] act as Lewis bases towards the metal halides of Group XI, MX, Group XII, MX2, and Group XIII, MX3, to form cluster compounds of the composition [{MXn}{Pt3(μ‐CO)3(PR3)3}]. The X‐ray crystal structure, NMR and IR data are given for the compound [{ZnI}{Pt3(μ‐CO)3(PPh(i‐Pr)2)3}].
New Polycyclic Compounds from Photochemical Rearrangements of Some Substituted 2‐Azatricyclo[5.2.2.01,5]undeca‐4,8,10‐trien‐3‐ones
Authors: Mihova Tonya R. , Trifonov Latchezar S. , Dimitrov Valentin S. , Orahovats Alexander S. , Linden Anthony , Heimgartner Heinz
Published: December 2004

The products formed on UV irradiation of several tricyclic compounds (i.e. 3, 6, 8, 15, and 17, Schemes 2‐4) were studied in detail. A marked dependence of the reaction course on the type and site of substitution was found. Among the several light‐induced transformations, a novel rearrangement, i.e. 11 to 9 (Scheme 3) was identified. The formation of the polycyclic compound 13 on irradiation of 8a (Scheme 3) resulted from an unexpected skeletal rearrangement with dearomatization of one benzene ring. The structures of compounds 10, 11, and 13 were established by X‐ray crystallography (Figs. 1‐3). An attempt was made to give a general mechanistic picture of all observed photochemical results (Schemes 4‐6).
Transesterifications with 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene/Lithium Bromide (DBU/LiBr) – Also Applicable to Cleavage of Peptides from Resins in Merrifleld Syntheses
Authors: Scebach Dieter , Thaler Adrian , Blaser Denis , Ko Soo Y.
Published: December 2004

A mixture of the amidine base 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) and LiBr (preferably 0,5 and 5 equiv., resp.) turns out to be a highly efficient catalyst (at 0–25°) for saponifications (in THF/H2O) and transesterifications (in ROH). The scope and limitations of the method are determined using ca. two dozens of different ester/alcohol combinations (Schemes 2 and 3). The investigation is focused on peptides as substrates. Under carefully controlled conditions, no epirnerization occurs with N‐Boc‐ and N‐Z‐protected peptide esters, when methyl, ethyl, isopropyl, or allyl esters are the products, as shown for peptides containing up to six amino acids, with Ala, Len MeLeu, Asp(OEt), or Tyr at the C‐terminus (Scheme 3 and Tables 1 and 2). Hydrolytic and transesterifying detachments of Boc‐Leu‐Ala‐Gly‐Val‐OR and Boc‐Leu‐Ala‐Gly‐Phe‐OR (R = H, Me) from PAM and Wang resins (1–8 h at 0–25°, 2 equiv. of DBU, 5 equiv. of LiBr) can be achieved by this method without epimerization of the C‐terrninal stereogenic center; a comparison with other methods (HF, Ti(OR)4) is given (Schemes 4 and 5). Possible protecting‐group strategies involving the DBU/LiBr method are discussed (Table 3), Extensive experimental details are given.
Aromatic nucleophilic substitution. Part 3. Preparation of novel 9‐oxo‐9H‐thioxanthene‐ and 9‐oxo‐9H‐xanthenedicarboximides and ‐dicarboxylates
Authors: Fischer Walter
Published: December 2004

By aromatic nucleophilic substitution followed by intramolecular acylation, 9‐oxo‐9H‐thioxanthene‐ and 9‐oxo‐9H‐xanthene‐dicarboximides were prepared from nitro‐ or chlorophthalimides and the dianions of thiosalicylic and salicylic acids (Scheme). The 9‐oxo‐9H‐thioxanthene‐3,4‐dicarboximides were converted to 9‐oxo‐9H‐thioxanthene‐3,4‐dicarboxylic‐acid derivatives such as anhydride, esters, and further imides. Some of these derivatives proved to be excellent photosensitizers with special properties such as liquid aggregation form, H2O solubility, solubility in lipophilic organic solvents and polymers, or bathochromic shifts of the absorption wavelengths.
Dimeric Metal Complexes as Mediators for Radical CC Bond‐Forming Reactions
Authors: Giese Bernd , Thoma Gebhard
Published: December 2004

Irradiation of dicarbonyl(η5‐cyclopentadienyl)iron dimer 1 or decacarbonyldimanganese (2) in the presence of alkyl halides leads to C‐centered radicals which can be trappedby alkenes and yields saturated and/or unsaturated addition products. Carbon radicals are generated via halogen abstraction by the initially formed metal‐centered radicals resulting from homolysis of the metal‐metal bond of dimeric mediators 1 and 2. No reaction occurs using octacarbonyldicobalt (3).
Base Hydrolysis of (Acidato)(Pentaamine) Complexes with Inert Metal Centers: Electronic Structure of the Intermediates, Requirements for Their Formation, and the Unique Reactivity of the Complexes of Cobalt(III)
Authors: Rotzinger François P. , Weber Jacques , Daul Claude
Published: December 2004

Molecular‐orbital calculations have been performed for the conjugate base cis‐[Co(NH3)4(NH2)Cl]+ and trans‐[M(NH3)4(NH2)Cl]+ (M = CrIII, CoIII, and RhIII), the hexacoordinated intermediates cis‐ and trans‐[Co(NH3)4(NH2)…Cl]+, the square‐pyramidal and trigonal bipyramidal pentacoordinated intermediates apical‐[Co(NH3)4(NH2)]2+, basal‐[Co(NH3)4(NH2)]2+, and equatorial‐[M(NH3)4(NH2)]2+ (M = Co and Rh), respectively, using modified extended Hückel and SCF MS‐Xα methods. The LUMO of the conjugate bases is an antibonding metal centered dρ* orbital which is stabilized during the dissociative activation of the MCl bond. For the above conjugate bases, separations of the highest doubly occupied MO (HDOMO) and the LUMO of 1.3, 2.5, 1.8, and 2.5 eV, respectively, have been calculated using the SCF MS‐Xα model. Only in the conjugate base cis‐[Co(NH3)4(NH2)Cl]+ with the smallest HDOMO — LUMO gap, the singlet electronic structure of the ground state may be stabilized by changing into a triplet when the CoCl bond is activated. This situation is unique to (acidato)(pentaamine)cobalt(III) complexes with deprotonated amine ligand cis to the leaving group and the reason for the existence of intermediates and their reactivity as well. Base hydrolysis of the analogues CrIII and RhIII complexes – the latter taken to represent the second‐ and third‐row transition‐metal amines – is unlikely to proceed via intermediates; a concerted substitution process is expected to take place.
Metabolic products of microorganisms. Part 262. The absolute configuration of sphydrofuran, a widespread metabolite from streptomycetes
Authors: Bindseil Kai U. , Henkel Thomas , Zeeck Axel , Bur Daniel , Niederer Daniel , Séquin Urs
Published: December 2004

Sphydrofuran (1) was isolated from the culture filtrate of Streptomyces sp. (strain Gö 28 and Tü 3616) by chemical screening methods. Metabolite 1 is an anomeric and ring‐chain tautomeric mixture and could easily be transformed into the stable furan derivative 2 under acidic conditions. The constitution and relative configuration of 1 was established by X‐ray crystallography of its 8‐O‐methyl derivative 3a. The absolute configuration at C(4) of 1 and thus of the whole molecule (3R,4S,5S) could be determined starting from 2 using the Helmchen method.
Synthesis of Aristotelia‐type alkaloids. Part VIII. Synthesis of (±)‐aristolasicone
Authors: Güller Rolf , Dobler Markus , Borschberg Hans‐Jurg
Published: December 2004

The revised structure of the indole alkaloid aristolasicone (2) was confirmed through a convergent total synthesis of the racemic form of this metabolite. The key step involves a one‐pot condensation/cyclization reaction between 1‐(4‐methoxyphenylsulfonyl)‐1H‐indole‐2‐acetaldehyde (9) and (±)‐trans‐5‐(2,6‐difluorobenzyloxy)‐p‐menth‐l‐en‐8‐amine ((±)‐7). The resulting allohobartine derivative (±)‐13, obtained in 84% yield, was deprotected and oxidized to (±)‐alloscrratenone ((±)‐15) which cyclized smoothly to the target molecule (±)‐2 upon exposure to BF3 · Et2O.
Synthesis of New Phospholipids Linked to Steroid‐Hormone Derivatives Designed for Two‐Dimensional Crystallization of Proteins
Authors: Lebeau Luc , Oudet Pierre , Mioskowski Charles
Published: December 2004

The synthesis of phospholipids 1n–3n, rationally designed for two‐dimensional crystallization of progesterone and estradiol receptors, is reported. The structure of these lipids provides them with essential properties such as fluidity and stability when spread into monolayers at the air/H2O interface, affinity for the protein to be crystallized, and accessibility of the ligand under the lipid monolayer.
Enzymatic Formation of Raucaffricine, the Major Indole Alkaloid of Rauwolfia serpentina Cell‐Suspension Cultures
Authors: Ruyter Carl Michael , Stöckigt Joachim H. H.
Published: December 2004

The major alkaloid from Rauwolfia serpentina cell‐suspension cultures, the glucoalkaloid raucaffricine (2), was enzymatically formed from vomilenine (1) and UDPG in presence of microsomal‐bound enzyme. This glucosyltransferase exhibits a relatively high substrate specificity with strong preference for 1 and UDPG. The apparent Km values for 1 and UDPG were 40 μM and 0.8 mM, respectively, for raucaffricine formation. Optimum transferase activity was observed at 50° and pH 6.3. The taxonomic distribution of this enzyme seems to be very limited because transferase can he exclusively detected in raucaffricine‐producing plant cells.
Synthese des Makrolid‐Antibiotikums (−)‐A26771B mit Photolactonisierung als Schlüsselreaktion und Computersimulation als effektive Optimierungshilfe
Authors: Quinkert Gerhard , Küber Frank , Knauf Wolfgang , Wacker Manfred , Koch Uwe , Becker Heinrich , Nestler Hans Peter , Dürner Gerd , Zimmermann Gottfried , Bats Jan W. , Egert Ernst
Published: December 2004

Synthesis of the Macrolide Antibiotic (−)‐A2677IB Using Photolactonization as a Key Reaction and Computer Simulation as an Effective Aid in Optimization

The title compound has been synthesized in a sequence of 21 steps starting from phenol. The cyclic skeleton has been built up in the earlier part of the synthesis by photolactonization. This reaction supplies C(6), with a functionality, not present in the target structure, but useful for oxygenation at C(4) and generation of the stereogenic center C(5). The Barton/McCombie reaction provides a product deoxygenated at C(6), but only after an adjacent oxirane ring has been opened at the cost of an increase in the number of overall steps. X‐Ray structural information and computational modelling of appropriate molecules proved to be essential to selection of optimal conditions for various transformations.
Characterization of Nitrosocarbonyl Compounds by Neutralization‐Reionization Mass Spectrometry
Authors: O'Bannon Patrick E. , Sülzle Detlev , Schwarz Helmut
Published: December 2004

The neutral molecules nitrosoformaldehyde (1a), 1‐nitrosoacetaldehyde (1b), and 2,2,2‐trifluoro‐1‐nitrosoacetaldehyde (1c) have been generated and detected by neutralization‐reionization mass spectrometry (NR‐MS).
Nucleotides. Part XXXVIII.. Syntheses and characterization of phosphorothioate analogues of (2′–5′) adenylate dimer and trimer and their 5′‐O‐monophosphates
Authors: Charubala Ramamurthy , Pfleiderer Wolfgang
Published: December 2004

The chemical syntheses of the phosphorothioate of (2′–5′)adenylate dimer (see 6a, 6b) and trimer (see 11a, 11b, 12a, 12b) as well as of their 5′‐monophosphates (see 15a, 15b, 16a, 16b) using the phosphoramidite method are described. The resulting diastereoisomer mixtures were separated into the pure components by chromatographical means. All synthetic intermediates were characterized by TLC, elemental analysis, and UV and 1H‐NMR spectra.
The Reaction of 9‐Bromoanthracene with Benzenethiolate Anion in Tetraglyme: Evidence against a competing electron‐transfer mechanism
Authors: Baumgarner Charles D. , Malen Alyssa H. , Pastor Stephen D. , Ali NabiRahni M.
Published: December 2004

The reaction of 9‐bromoanthracene (1) with benzenethiol(ate) in tetraglyme proceeds by a SNAr mechanism. The concurrent formation of anthracene is not due to a competing single‐electron‐transfer pathway involving either benzenethiol or benzenethiolate anion.
1,2‐Stereoinduction in Radicals and Anions: A comparison between hydrogen abstraction and protonation
Authors: Erdmann Peter , Schäfer Jörg , Springer Ronald , Zeitz Heinz‐Georg , Giese Bernd
Published: December 2004

Chiral enolates 5 and 10, generated by radical addition and subsequent reduction, show diastereofacial selectivity during protonation. In the presence of substituted amines, diastereoselectivity is enhanced and becomes comparable to radical stereoselection. Diastereoselectivities up to 99:1 and yields up to 90% are reached.
Synthesis of Selectively Substituted Lipocyclopolyamines
Authors: Brand Guy , Hosseini Mir Wais , Ruppert Romain
Published: December 2004

A general synthetic strategy for the preparation of polyazamacrocycles containing long aliphatic chains is reported. These compounds are 22‐ or 24‐membered hexaazamacrocycles incorporating two diethylenetriamine subunits (H2NCH2CH2NHCH2CH2NH2) linked together either by two CH2CH2OCH2CH2 (see 4–6), two tetramethylene (see 7), or two pentamethylene (see 8) fragments. Whereas for compound 4, one of the centrally located amine functionalities of the triamine subunit bears a hexadecyl chain, for compound 5, two of such chains are centrally attached to both subunits. In macrocycles 6–8, all six amino functionalities bear hexadecyl chains. Compounds 4–8 are potential candidates for the construction of selective chemical sensors such as specific electrodes for adenosine mono‐, di‐, and tri‐phosphate. They may also be used for nucleoside polyphosphates extraction and/or transport.
Spiro[1,3‐benzoxathiepin‐4(5H),1′‐cyclohexa[2,4]diene]‐2,2′‐dione, a Novel Heterocyclic Ring System
Authors: Kolly Sandra , Meier Hansrudolf , Winkler Tammo
Published: December 2004

The 4,4′,6,6′‐tetrasubstituted 2,2′‐alkylidenebis(phenols) 1 reacted with CISCOI to give spiro[1,3‐benzoxathiepin‐4(5H), 1′‐cyclohexa[2,4]diene]‐2,2′‐diones 4, together with cyclic carbonates 5. The structures of the products were elucidated mainly by 13C‐NMR and 1H‐NMR spectroscopy.
Aspidosperma Alkaloids. A New Didehydrodimerization Mode of β‐Anilinoacrylic Alkaloids by Anodic Oxidation
Authors: Palmisano Giovanni , Danieli Bruno , Lesma Giordano , Santagostino Marco , Fiori Giorgi , Toma Lucio
Published: December 2004

A regio‐ and stereoselective didehydrodimerization procedure, whose key step involves the anodic oxidation, allows the conversion of β‐anilinoacrylic alkaloids belonging to the Aspidosperma class, typified by tabersonine (1) and its 3‐oxo derivative 2, into the hitherto unknown 16,10′‐didehydro dimers 3 and 7, respectively.
The H/D Exchange and Hydrogenolysis of Butane on an Alumina‐Supported Nickel Catalyst
Authors: Öz Hami , Gäumann Tino
Published: December 2004

The exchange of butane with deuterium on a nickel/alumina catalyst is studied over a wide range of temperatures (50–230°) and for three hydrocarbon/deuterium ratios. The initial distribution is used to propose a reaction scheme by considering different adsorbed species such as: alkyl‐(α), alkene‐(α, β) and allyl‐(α,β,γ) species, where α, β, and γ are different C‐atoms. It is assumed that each adsorbed species can either desorb directly while exchanging one, two, and three H‐atoms or undergo multiple exchange before desorption. It is shown that by reducing the activity of the catalyst a back‐exchange of the fully deuterated species sets in a lower temperature; a systematic deviation of all model calculations for the estimation of the concentrations of the C4HD9 and C4D10 is, thus, explained. The exchange of CH3CD2CD2CH3 and CD3CH2CH2CD3 with H2 and D2 is also studied, and similar results are obtained as with exchanges of CH3CD2CH3 and CD3CH2CD3. With the help of very‐high‐resolution mass spectra, it is shown that the initial degree of deuteration, i. e. the degree of deuteration after one adsorption step, is 84% for the methylene and 57% for the methyl group respectively. The hydrogenolysis reactions of butane is studied in the same system between 180° and 230°. A wide range of conversion is covered, and the product distributions are fitted to kinetic equations in order to obtain the initial rate constants. On the nickel/alumina catalyst one or several C–C bonds are broken before the desorption of the species. Under the conditions used in these experiments, the surface cracking is the rate‐limiting step. An isotope effect is observed for the decomposition in D2, the production of propane being favored.
Phenols and Quinones from Seeds of Different Iris Species
Authors: Marner Franz‐Josef , Horper Wolfgang
Published: December 2004

The seed oils of I.pseudacorus LINN., I.sibirica LINN., and I.missouriensis NUTTAL. contain appreciable amounts of phenols, quinones, and resorcinols, substituted with homologous alkyl or alkenyl side chains. The structure elucidation of these compounds is described, and their possible biosynthesis is discussed.
New 2,2′‐Bipyridine Derivatives and Their Luminescence Properties with Europium(III) and Terbium(III) Ions
Authors: Mukkala Veli‐Matti , Kankare Jouko J.
Published: December 2004

Twenty differently substituted 2,2′,2″,2‴ ‐[(2,2′‐bipyridine‐6,6′‐diyl)bis(methylenenitrilo)]tetrakis(acetc acids) 75–94 were synthesized with the purpose of developing new markers to be used in bioaffinity assays based on the unique luminescence properties of EuIII and TbIII ions. The relative luminescence yields, excitation maxima, and emission decay constants were determined for the corresponding EuIII and TbIII chelates. The substituents at the bipyridine moiety had a significant effect on the luminescence properties: the best relative luminescence yields R were obtained for ligands with electron‐donating substituents (e.g. Me, Ph), electron‐withdrawing substituents (e.g. NO2, COOH) had a reverse effect. However, no clear correlation between the relative luminescence yields and the substituent parameters was found.
An Enantioselective Approach to the Taxanes: Direct access to functionalized cis‐tricyclo[9.3.1.03,8]pentadecanes via α‐hydroxy ketone and Wagner‐Meerwein rearrangements
Authors: Paquette Leo A. , Elmore Steven W. , Combrink Keith D. , Hickey Eugene R. , Rogers Robin D.
Published: December 2004

The feasibility of the titled reactions for the rapid, enantioselective synthesis of cis‐tricyclo[9.3.1.03,8]pentadecane precursors to taxusin and taxol has been examined. The catalysts most well suited to inducing the appropriate 1,2‐shifts have been identified. To a great extent, the rearrangement products are formed as a direct consequence of appropriate structural features (kinetic phenomenon) and strain minimization (thermodynamic driving force). Complementary MM2 calculations of the global minimum in each series provided indications that were completely in line with the experimental observations. Sophisticated NMR studies and X‐ray crystallographic determinations were coordinated to remove any ambiguity of product structure and solid‐state conformation.
Conformational Studies of Marine Polyhalogenated α‐Chamigrenes Using Temperature‐dependent NMR spectra inverted‐chair and twist‐boat cyclohexane moieties in the presence of an axial halogen atom at C(8)
Authors: Guella Graziano , Chiasera Giuseppe , Pietra Francesco
Published: December 2004

α‐Chamigren‐3‐one (+)‐8 bearing an axial CI‐atom at C(8) exists as a largely dominant conformer with Me—C(5) at the envelope‐shaped enone ring pointing away from CIax−C(8) at the cyclohexane ring (= B) in the ‘normal’ chair conformation, as shown by 1H‐NMR. In contrast, the α‐chamigren‐3‐ols (+)‐9 and (+)‐10, obtained from hydride reduction of (+)‐8, show a temperature‐dependent equilibrium of conformers where the major conformers have ring B in the inverted‐chair (and twist‐boat for (+)‐9) conformation to avoid repulsions between Me−C(5) and CIax–C(8) (Scheme 1). This is in agreement with the conformation of the epoxidation product (+)‐12 of (+)‐9 where Me–C(5) is pushed away from CIax–C(8) in a ring‐B chair similar to that of (+)‐8 (Scheme 2). Introduction of a pseudoequatorial Br‐atom at C(2) of (+)‐8, as in enone (+)‐15 (Scheme 3), does not affect the conformation; but a pseudoaxial BrC(2) experiences repulsive interactions with Heq–C(7), as shown by the 1H‐NMR data of the isomeric enone (+)‐16 where the ‘normal’‐chair conformer Cβ‐16 is in an equilibrium with the inverted chair conformer ICβ‐16 (Scheme 3). These results and the accompanying paper allow a unifying view on the conformational behavior of marine polyhalogenated α‐chamigrenes. This view is supported by the acid‐induced isomerization of α‐chamigrene (+)‐9 (inverted chair) to β‐chamigrene (+)‐17 (‘normal’ chair; Scheme 4), the driving force being the lesser space requirement of CH2C(5) than of Me–C(5). This explains why β‐chamigrenes are so common in nature.
Fünf‐ und sechsgliedrige cyclische Phosphonsäure‐diamide und‐thioester‐amide sowie Spirobi[oxazaphosphole]
Authors: Neidlein Richard , Buseck Stephan
Published: December 2004

Five‐ and Six‐Membered Cyclic Phosphonic Diamides, Thioester‐amides and Spirobi[oxazaphospholes]

By reaction of the 1,2‐diaminobenzene derivatives 1a–d with the phosphonoyl dichlorides 2a–g, the 1,3‐dihydro‐1,3,2‐benzodiazaphosphol‐2‐ones 4a–q are obtained. The phosponoyl dichlorides 2a–e, 2g, and 2h yield with naphthalene‐1,8‐diamines (5) the diazaphosphinones 6a–g under similar reaction conditions. The thiazaphosphole oxides 9a–d are accessible by reaction of the phosphonoyl dichlorides 2a–d with 2‐aminobenzenethiol (7). Unexpectedly, the reaction of the dichlorides 2a and 2b with 2‐aminophenol (10) led to the spirobi[oxazaphospholes] 13a and 13b, respectively.
A Novel Heterocyclic Ring System: Synthesis and Spectral Data of 4,8,9b‐Triazacyclopenta[c, d]phenalene
Authors: Hou Dongfeng , Balli Heinz
Published: December 2004

The synthesis and 1H‐NMR and electronic absorption spectra of 4,8,9b‐triazacyclopenta[c, d]phenalene and several of its derivatives are described.
Hydrogenation of the ansa‐Chain of Rifamycins. X‐ray crystal structure of (16S)‐16,17,18,19‐tetrahydrorifamycin S
Authors: Bartolucci Cecilia , Cellai Luciano , Filippo Patrizia Di , Lamba Doriano , Segre Anna Laura , Bianco Armando Doriano , Guiso Marcella , Pasquali Vinicio , Brufani Mario
Published: December 2004

The catalytic hydrogenation of rifamycin S (2) over Pd/C, followed by oxidation with K3[Fe(CN)6], generates a pair of 16,17,18,19‐tetrahydrorifamycins S (3/4), epimeric at C(16). The use of PtO2 as catalyst leads to the hydrogenation also of the C(28)C(29) bond giving, after oxidation by K3[Fe(CN)6], a mixture of the epimers (16R)‐ and (16S)‐16,17,18,19,28,29‐hexahydrorifamycins S (5/6). Furthermore, we synthesized the (16R)‐ and (16S)‐3‐bromo derivatives 7/8 and (16R)‐ and (16S)‐3‐(piperidin‐1‐yl) derivatives 9/10. The determination of the X‐ray crystal structure of the most abundant epimer 4 of the tetrahydrorifamycins allowed the assignment of the absolute configuration at C(16) of all derivative. A Structure‐activity relationship study showed that in general the (16R)‐epimers are more potent inhibitors of bacterial RNA polymerase than the (16S)‐epimers.
Synthesis and Structure of a p‐Terphenoquinone and Paramagnetic Species Derived Therefrom
Authors: Boldt Peter , Bruhnke Detlev , Gerson Fabina , Scholz Markus , Jones Peter G. , Bär Friedrich
Published: December 2004

3,5,3″,5″‐Tetra(tert‐butyl)‐p‐terphenoquinone (12b) was synthesized and characterized by its spectroscopic and X‐ray structural data. The ground state of 12b is singlet with a strong contribution of a biradical structure. Paramagnetic derivative of 12b, such as the semiquinone radical anion (12bτ) and its O‐protonated form, the phenoxy radical (18), were studied by ESR and ENDOR spectroscopy.
A Convenient Procedure for he Synthesis o 2,3,4,6‐Tetra‐O‐benzyl‐D‐gluconolactam and D‐Nojirilactam
Authors: Hoos Roland , Naughton Andrew B. , Vasella Andrea
Published: December 2004

Swern oxidation of 2,3,4,5‐tetra‐O‐benzyl‐D‐glucose (1) followed by ammonolysis gave the crystalline amide 3 which was oxidized (DMSO/pyridine · SO3) to yield the oxo‐amide 4 and the hydroxy‐lactams 5 and 6. Cyclization of 4 to the very slowly equilibrating 5 and 6 was completed by treatment with AcOH in CHCl3. The configuration of the hydroxy‐lactams was assigned on the basis of NOEs. Reduction (Et3SiH/BF3 · Et2O) of the hydroxy‐lactams either individually or as a mixture led to 2,3,4,6‐tetra‐O‐benzyl‐D‐gluconolactam (7). The procedure, based upon modifications of a patent, does not require chromatography; the overall yield of 7 from 1 is 43%. Hydrogenolysis of 7 gave D‐nojirilactam (8); benzylation led to the known pentabenzyl‐D‐nojirilactam (9) and to the unsaturated lactam 10.
Complex Formation of PdII Ion with the Tripodal Ligand Tris[2‐(dimethylamino)ethyl]amine
Authors: Anderegg Giorgio , Melichar Zdenek
Published: December 2004

The complex formation of PdII with tris[2‐(dimethylamino)ethyl]amine (N(CH2CH2N(CH3)2)3, Me6tren) was investigated at 25° and ionic strength I = 1, using UV/VIS, potentiometric, and NMR measurements. Chloride, bromide, and thiocyanate were used as auxiliary ligands. The stability constant of [Pd(Me6tren)]2+ in various ionic media was obtained: log β([Pd(Me6tren)] = 30.5 (I = 1(NaCl)) and 30.8 (I = 1(NaBr)), as well as the formation constants of the mixed complexes [Pd(HMe6tren)X]2+ from [Pd(HMe6tren)(H2O)]3+:log K = 3.50 = Cl−) and 3.64 (X− = Br−) and [Pd(Me6tren)X]+ from [Pd(Me6tren)(H2O)]2+: log K = 2.6 (X− = Cl−), 2.8(Br−) and 5.57 (SCN−) at I = 1 (NaClO3). The above data, as well as the NMR measurements do not provide any evidence for the penta‐coordination of PdII, proposed in some papers.
Pteridines. Part C. Structure and nonenzymatic synthesis of aurodrosopterin
Authors: Yim Jeongbin , Kim Sujeong , Walcher Gunter , Pfleiderer Wolfgang
Published: December 2004

The nonenzymatic synthesis of aurodrosopterin (5) from 6‐acetyl‐2‐amino‐3, 7, 8, 9‐tetrahydro‐4H‐pyrimido‐[4,5‐b][1,4]diazepin‐4‐one (3) and 7,8‐dihydrolumazine (4) at pH 3 (HCl) was performed. The identity of the synthesized compound with the natural eye pigment isolated from drosophila heads was confirmed by thin‐layer chromatography on cellulose and by comparisons of the 1H‐NMR and UV/VIS spectra. The nonenzymatic synthesis of a neodrosopterin‐like red pigment from 3 and 2,4‐diamino‐7,8‐dihydropteridine was also carried out, but its identity could not be established. This pigment, called aminodrosopterin, has an absorption peak at 489 nm, which is very close to that of neodrosopterin.
Structures and Chemistry of Methanofullerenes: A Versatile Route into N‐[(Methanofullerene)carbonyl]‐Substituted Amino Acids
Authors: Isaacs Lyle , Diederich François
Published: December 2004

The reaction of C60 with oxadiazole 13 afforded the dimethoxymethanofullerene 7 in 32% yield as a 6‐6‐ring‐bridged isomer with a closed transannular bond. A literature survey showed that all 6‐6‐ring‐bridged methanofullerenes are σ‐homoaromatic with a closed transannular bond (6‐6‐closed) and all 6‐5‐ring‐bridged are π‐homoaromatic with an open transannular bond (6‐5‐open). The preference for 6‐6‐closed and 6‐5‐open structures is not due to substituent effects but is best explained with the conservation in these isomers of the favorable bonding seen in C60 with higher double‐bond character at 6‐6 bonds and higher single‐bond character at 6‐5 bonds. Reaction of C60 with diazo diester 15 gave the fullerene diester 14 which was hydrolyzed with BBr3 in benzene to the methanofullerenecarboxylic acid 10, a versatile synthon for the preparation of amphiphilic fullerene derivatives. Treatment of 10 with alcohols and amino acid esters under DCC coupling conditions afforded the esters 5 and 17 and the amino‐acid derivatives 11 and 12, respectively.
Anatolioside E: A New Acyclic Monoterpene Glycoside from Viburnum orientale
Authors: Çaliş Ihsan , Yürüker Ayşen , Rüegger Heinz , Wright Anthony D. , Sticher Otto
Published: December 2004

A new open‐chain monoterpene glycoside, anatolioside E (1), was isolated from the leaves of Viburnum orientale in addition to three known acyclic monoterpene glycosides, betulalbusides A (2) and B (3), and 2(E)‐2,6‐dimethyl‐2,7‐octadien‐1,6‐diol‐6‐O‐β‐D‐glucopyranoside(4). The structure of anatolioside E (1) was elucidated on the basis of chemical and spectral data as 6‐O‐[β‐D‐glucopyransoyl‐(1‴‴ → 6‴″)‐2‐(E), 6(R), 2,6‐dimethyl‐6‐hydroxy‐2,7‐octadienoyl‐(1‴″ → 2″″)‐β‐D‐glucopyranosyl‐(1″″ → 6‴)‐2‐(E), 6(R), 2,6‐dimethyl‐6‐hydroxy‐2,7‐octadienoyl‐(1‴ → 4″)‐α‐L‐rhamnopyranosyl‐(1″″ → 2′)‐β‐D‐glucopyranosyl]linalool.
Glycosylidene Carbenes. Part 13. Synthesis and thermolysis of representative 1‐azi‐glycoses
Authors: Vasella Andrea , Witzig Christian , Waldraff Christian , Uhlmann Peter , Briner Karin , Bernet Bruno , Panza Luigi , Husi René
Published: December 2004

In the context of the hypothesis postlating a heterolytic cleavage of a CN bond during thermolysis of alkoxydiazirines (Scheme 1), we report the preparation of the diazirines 4, 5, 7, and 8, the kinetic parameters for the thermolysis in MeOH of the diazirines 1 and 4–9, and the products of their thermolysis in an aprotic environment. The diazirines 4, 57, and 8 (Scheme 2–5) were prepared from the known hemiacetals 10, 19, 34 (prepared from 31 in an improved way), and 42 according to an established method. The oximes 11, 20, 35, and 43 were obtained from the corresponding hemiacetals as (E/Z)‐mixtures; 43 was formed together with the cyclic hydroxylamine 44. Oxidation of 11, 35, and 43 (N‐chlorosuccinimide/1,8‐diazabicyclo[5.4.0]undec‐7‐ene (NCS/DBU) or NaIO4) gave good yields of the (Z)‐hydroximolactones 12, 36, and 45, while the oxime 20 led to a mixture of the (E)‐ and (Z)‐hydroximolactones 21 and 22, which adopt different conformations. Their configuration was assigned, inter alia, by a comparison with the enol ethers 28 and 29, which were obtained, together with 30, from the reaction of the diazirine 5 with benzaldehyde and PBu3. Treatment of the hydroximolactone O‐sulfonates 13, 23, 37, and 46 with NH3/MeOH afforded the diaziridines 15, 25, 38, and 47 in good yields, while the (E)‐sulfonate 24 decomposed readily. Oxidation of the diaziridines gave 4, 5, 7, and 8, respectively. Thermolysis of the diazirines 1 and 4–9 in MeOH yielded the anomeric methyl glycosides 50/51, 16/17, 26/27, 52/53, 39/40, 48/49, and 54/55, respectively. A comparison of the kinetic data of the thermolysis at four different temperatures shows the importance of conformational and electronic factors and is compatible with the hypothesis of a heterolytic cleavage of a CN bond. An early transition state is evidenced by the absence of torsional strain by an annulated 1,3‐dioxane ring. Thermolysis of 1 in MeCN at 23° led mostly to the diasteroisomeric (Z,Z)‐, (E,E)‐, and (E,Z)‐lactone azines 56, 57, and 58 (Scheme 6), which convert to 56 under mild conditions, and to 59 (3%). The benzyloxyglucal 59 was obtained in higher yields (18%), together with 44% of 56–58, by thermolysis of solid 1. Similarly, thermolysis at higher temperatures of 4 in toluene, THF, or dioxane and of 9 in CH2Cl2 or THF yielded the (Z,Z)‐lactone azines 60 and 61, respectively, the latter being accompanied by the dihydro‐oxazole 62.
Single‐Crystal Structure of the Solvent‐Separated Radical Ion Pair [9,10‐diphenylanthracene.⊖][Na⊕(THF)6] and its implication for cation solvation
Authors: Bock Hans , John Andreas , Näther Christian , Havlas Zdenek , Mihokova Eva
Published: December 2004

The one‐electron transfer to large π‐delocalized hydrocarbons provides an interesting possibility to crystallize solvent‐separated ion‐pair salts containing optimally solvated cations. Accordingly, the reduction of 9,10‐diphenylanthracene in aprotic THF solution at a sodium metal mirror allows to grow dark‐blue prismatic crystals of its radical anion and sixfold THF‐solvated sodium cation. The structure of the radical anion is very similar to that recently published for the neutral molecule. According to AM1 hypersurface calculations based on the structural data, the phenyl twist angles obviously must be determined by lattice packing, and the negative charge is delocalized predominantly within the anthracene π system. The counter cation [Na⊕(THF)6], reported ordered for the first time, shows nearly octahedral coordination within a rather densily packed solvent shell. Due to the strong repulsions between the solvent molecules, its isodesmically calculated solvation enthalpy is smaller than that of the analogous dimethoxyethane complex [Na⊕(DME)3].