bluuebunny/crossref_metadata_2025 huggingface dataset:
Total synthesis of angucyclinones, 6. Synthesis of naturally (MM 47755; X‐14881 E) and non‐naturally occurring aromatic angucyclinones
Authors: Krohn Karsten , Khanbabaee Karamali , Micheel Jörg
Published: July 2007

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

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

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

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

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

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

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

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

N‐Sulfonylalkylamines 2a, b react with ynamines 3 to give primarily 2H‐1,2‐thiazete 1,1‐dioxides 4. But, except for the 4‐triphenylsilyl species 4a, b, these products are unstable and undergo electrocyclic ring opening to very reactive amidinosulfenes 5, which are transformed into different products, depending on the ynamine substituents R2. The 1,3‐dithietane 1,1,3,3‐tetraoxide 8 is formed from N‐sulfonylisopropylamine (2a) and the trimethylsilyl‐substituted ynamine 3b via amidinosulfene 5c and probably thioketene S,S‐dioxide 7. On the other hand, (isopropylamidino)sulfene 5d dimerizes to the 2H‐1,5,2‐dithiazine 9 and also gives the [2 + 4] cycloadducts 10a, 11a by reaction with 2a and ynamine 3c, respectively. In contrast, it was possible to trap phenyl‐substituted amidinosulfenes 5e‐h by addition of water or methanol.
Molecular modeling of saccharides, 7. The conformation of sucrose in water: A molecular dynamics approach
Authors: Immel Stefan , Lichtenthaler Frieder W.
Published: July 2007

A molecular mechanics analysis of the conformational properties of sucrose in vacuo in terms of the intersaccharidic torsion angles Φ and Ψ, revealed three energy minima. The geometry of the global minimum‐energy closely resembles the solid‐state structure. Most notably, the interresidue hydrogen bonding interaction 2g‐O…︁HO‐1f present in the crystal, is retained under vacuum boundary conditions, indicating the molecular geometries adopted in the crystal lattice and in vacuo to be similar. For aqueous solutions, detailed molecular dynamics simulations of sucrose „soaked”︁ with 571 water molecules in a periodic box (truncated octahedron), revealed this direct H‐bond interaction to be replaced by an indirect, water‐mentioned one: an interresidue water‐bridge of the 2g‐O…︁H2O…︁HO‐1f type prevailed with a high significance and a long life‐time. This means the linkage geometry of sucrose in water–despite the absence of direct interresidue hydrogen bonds–again closely resembles the solid‐state and in vacuo geometry in terms of the orientation of the glucose and the fructose unit relative to one another. The solution dynamics of, and the hydration around sucrose were analyzed in terms of pair distribution functions. These indicate strong hydrogen bonding between all sucrose hydroxyls (as donors and acceptors) and water within a first, well‐defined hydration layer (hydroxyl‐oxygen–water distances 1.8–3.5 Å), whereas the acetalic oxygens are engaged to a lesser extent as H‐bond acceptors. The second hydration shell (>4 Å) is rather diffuse and less pronounced, indicating those water molecules to be in a disordered state. The implications of the hydration shell and the water bridge on the crystallization process of sucrose and on binding towards transporter proteins, and the sweet‐taste receptor, are discussed. Other sucrose conformations that may conceivably exist in aqueous solution, may have eluded the MD simulation search. The umbrella sampling technique was applied for establishing the free energy profile as a function of the intersaccharidic torsion angles. The resulting concise picture of the dynamics of sucrose in aqueous solution, encompassing the entire conformational space available, revealed only two energy minima. Of these, the by far, most populated global minimum structure corresponded to the most stable solution geometry, as found by molecular dynamics.
Utilization of industrial waste materials, 5. Synthesis of new, chiral 1,3,2‐oxazaphospholidine‐borane complexes and attempts to apply them in the stereoselective synthesis
Authors: Peper Viola , Stingl Klaus , Thümler Hajo , Saak Wolfgang , Haase Detlev , Pohl Siegfried , Jugé Sylvain , Martens Jürgen
Published: July 2007

New, chiral 1,3,2‐oxazaphospholidine‐borane complexes 3a‐b and 8a‐d were synthesized from the β‐amino alcohols 1a‐b and 6a‐d. The borane complexes 3, 8a, 8c, and 8d were allowed to react with different organolithium compounds and afforded the corresponding aminophosphane‐borane complexes 4a–c and 9a‐g. Acid methanolysis of those complexes led to the formation of the phosphinite‐borane complexes 5a‐c. This is a further example of the utilization of the industrial waste material (all‐R)‐2‐azabicyclo‐[3.3.0]octane‐3‐carboxylic acid. The catalytic efficiency of the chiral 1,3,2‐oxazaphospholidine‐borane complexes 3a, 3b, and 8c was examined in the enantioselective borane reduction of some ketones.
Synthesis of Vinylallenes by Conjugate 1,6‐, 1,8‐, 1,10‐ and 1,12‐Addition Reactions of Organocuprates with Acetylenic Michael Acceptors and Their Use as Dienes in Intermolecular Diels‐Alder Reactions
Authors: Koop Ulrich , Handke Gabriele , Krause Norbert
Published: July 2007

Various vinylallenes were synthesized by conjugate cuprate additions to acetylenic Michael acceptors. Thus, 1,6‐addition reactions with 2‐en‐4‐ynoates 1, 3, and 5a, respectively, furnished vinylallenes 2, 4, and 7 after regioselective electrophilic capture of the allenyl enolates formed. Likewise, 1,8‐addition to 2,4‐dien‐6‐ynoates 8a and 10 gave the vinylallenes 9 and 11, whereas the 1,10‐addition of Me2CuLi to 2,4,6‐trien‐8‐ynoate 12 provided allene 13, and the analogous 1,12‐addition to 2,4,6,8‐tetraen‐10‐ynoate 14 furnished the polyene 15. These vinylallenes are valuable dienophiles in regio‐ and stereoselective Diels‐Alder reactions, as evidenced by the formation of the cycloaddition products 16–24. In the presence of Lewis acids, vinylallene 4a presumably rearranges to a cyclopentadiene derivative which then forms the cycloadducts 25 and 26.
New Efficient, Flexible and Regioselective Synthesis of 2,4‐Di‐ and 2,3,4‐Trialkylated an Arylated 1H‐Pyrroles
Authors: Enders Dieter , Maaßen Ralf , Han Sin‐Ho
Published: July 2007

Starting from easily available 2‐acetoxy aldehyde dimethylhydrazones rac‐2, we prepared various alkyl‐ and aryl‐substituted 1H‐pyrroles 6 in good overall yield. The titariummediated a2‐umpolung reaction of rac‐2 with different acyclic and cyclic silyl enol ethers 3 leads directly or via 4‐oxo hydrazones rac,anti‐4 to 1‐(dimethylamino)‐1H‐pyrroles 5. A novel method for the reductive removal of the dimethylamino group affording 1H‐pyrroles 6 is presented.
Pyrrolo‐ and Thiophenoperylenedicarboximides – Highly Fluorescent Heterocycles
Authors: Langhals Heinz , Feiler Leonhard
Published: July 2007

Pyrrolo‐ and thiophenoperylenedicarboximides 4 and 7 were prepared by reductive cyclization of 1‐nitroperylenedicarboximides 3 and 5 with phosphorous acid esters and sulfur, respectively. The imides 4 and 7 are highly fluorescent and are easily monofunctionalized by nucleophilic substitution reactions which makes them useful for fluorescent labeling.
Prearranged Glycosides, 4!. Synthesis via Prearranged Glycosides of a Tetrasaccharide Fragment Related to the Capsular Polysaccharide of Streptococcus pneumoniae Type 27
Authors: Schüle Gunter , Ziegler Thomas
Published: July 2007

The blockwise synthesis of the pyruvated tetrasaccharide 4,6‐(S)‐pyruvic‐acetal‐β‐d‐GlcNAcp‐(1→3)‐α‐d‐Galp‐(1→4)‐β‐l‐Rhap‐(1→4)‐β‐d‐Glcp‐O(CH2)5NH2 (32), related to the repeating unit of the capsular polysaccharide of Streptoccus pneumoniae type 27, by coupling of the suitably protected disaccharide blocks 4,6(S)‐pyruvic‐acetal‐β‐d‐GlcNAcp‐(1→3)‐α‐d‐Galp‐trichloroacetimidate (13) and β‐l‐Rhap‐(1→4)‐β‐d‐Glcp‐O(CH2)5NHZ (29β) is described. The latter disaccharide acceptor was prepared via prearranged glycosides by intramolecular glycosylation of a protected 5‐aminopentyl β‐d‐glucopyranoside linked by a succinyl bridge at C‐3 to C‐2 of ethyl 1‐thio‐α‐l‐rhamnopyranoside. The dependence of the anomeric selectivity of the coupling on the nature of the protecting group at C‐4 of the rhamnosyl moiety is studied.
[3 + 2] Cycloadditions of Nitrile Oxides to C70 Affording 4,5‐Dihydroisoxazoles and Their Structure Determination
Authors: Irngartinger Hermann , Köhler Claus‐Markus , Baum Gerhard , Fenske Dieter
Published: July 2007

Three isomeric monoadducts 2aA, 2aB, and 2aC of fullerene‐70 with 2,4,6‐trimethoxybenzonitrile oxide 1a were synthesized and isolated. With a combination of FAB‐MS, 13C‐ and 1H‐NMR spectroscopy the structure of the orientational and regioisomers could be assigned. A precise X‐ray structure analysis of the isomer 2aA with the substituent placed above the pole could be performed at low temperature (170 K). The corresponding monoadduct 3a of C60 was synthesized, isolated and characterized. In the same manner a mixture of three isomeric monoadducts 2b of C70 with ethoxycarbonylnitrile oxide 1b was obtained and characterized. The monadducts 2c of C70 with 9‐anthrylnitrile oxide 1c were characterized by FAB‐MS.
Synthesis of New Nepenthone Derivatives
Authors: Marton János , Szabó Zoltán , Simon Csaba , Hosztafi Sándor , Makleit Sándor
Published: July 2007

Hydrogenation of nepenthone (3a) leads to a mixture of dihydronepenthone (3c) and the secondary alcohol (20S)‐4b. The enantiomeric secondary alcohol (20S)‐4b is prepared from the 7α‐formyl‐6,14‐ethenomorphinan derivative 3b by reaction with phenylmagnesium bromide to afford a mixture of the diastereoisomeric alcohols 4a. Hydrogenation of 4a leads to (20S)‐4b and (20R)‐4b, which are separated by fractional crystallization. The conformations of (20S)‐4b and (20R)‐4b are determined by NOE difference experiments.
Synthesis and Properties of 2‐Carboxyalkyl‐1,2‐benzisoselenazol‐3(2H)‐ones and Related Organoselenium Compounds as Nitric Oxide Synthase Inhibitors and Cytokine Inducers
Authors: Mlochowski Jacek , Juchniewicz Leszek , Kloc Krystian , Gryglewski Ryszard J. , Jakubowski Andrzej , Inglot Anna D.
Published: July 2007

A convenient synthesis of the 2‐carboxyalkyl‐1,2‐benzisoselenazol‐3(2H)‐ones 4a–k and their esters 41–p from 2‐(chloroseleno)benzoyl chloride (2) and amino acids or their carboxy esters is reported. In similar way other 2‐substituted 1,2‐benzisoselenazol‐3(2H)‐ones 4q–u were synthesized. The related bis[2‐(carbamoyl)phenyl] diselenides 5 were obtained by reductive conversion of 1,2‐benzisoselenazol‐3(2H)‐ones 4 or directly by the reaction of bis[2‐(chlorocarbonyl)phenyl] diselenide (3) with compounds having a primary amino group. It was found that some of compounds 4 and 5 are modest cytokine (TNF, IFN) inducers in human peripheral blood leucocyte cultures and block the constitutive endothelial nitric oxide synthase (ce NOS).
A Generalized Solvent Basicity Scale: The Solvatochromism of 5‐Nitroindoline and Its Homomorph 1‐Methyl‐5‐nitroindoline
Authors: Catalán Javier , Díaz Cristina , López Vicenta , Pérez Pilar , De Paz José‐Luis G. , Rodríguez José Gonzalo
Published: July 2007

A total of 202 organic solvents and the gas phase were placed on a solvent basicity scale for hydrogen bond acceptor based on parameter SB. The value of such a parameter can readily be determined from the UV/Vis spectrum for an appropriate acid probe (5‐nitroindoline) (NI) and its non‐acid homomorph (1‐methyl‐5‐nitroindoline) (MNI). The proposed scale can advantageously substitute the more widely used solvent scales such as Gutmann's donor number (DN), the Koppel‐Palm B(MeOD) scale, and the Taft‐Kamlet β scale. While data for the proposed scale are derived only from electronic transitions, they are accurately descriptive of solvent basicity in both spectroscopy (UV/Vis, IR and NMR) and miscellaneous chemical areas (thermodynamic, kinetics, and electrochemistry).
Dyotrope Wasserstoffübertragung in Dihydrosesqui‐ und in Dihydro‐syn‐sesterbicyclo[2.2.2]octenen
Authors: Grimme Wolfram , Pohl Kathrin , Wortmann Jens , Frowein Dirk
Published: July 2007

Dyotropic Hydrogen Transfer in Dihydrosesqui‐ and in Dihydro‐syn‐sesterbicyclo[2.2.2]octenes

The intramolecular dyotropic hydrogen transfer is studied in dihydrosesquibicyclo[2.2.2]octenes. In the parent system 4‐d2 the process transfers two hydrogen atoms from the ethano to the etheno bridge; it is thermoneutral and reversible at 200°C, In 12a, b a 1,2‐dihydrobenzene acts as the hydrogen donor; the reaction is highly exothermic and occurs already at room temperature. In 19‐d4 the dyotropic hydrogen exchange from a 1,2‐dihydrobenzene to benzene is again thermoneutral and occurs at 200°C. The kinetic parameters of these reactions, listed in Table 7, indicate a concerted pericyclic pathway. In the extended dihydro‐syn‐sesterbicyclo[2.2.2]octenes 6‐d2 and 15a, b two hydrogen transfers occur in sequence, the central bridge serving as a relais. Here the dyotropic processes establish equilibria between structures with stacked and isolated double bonds, allowing an evaluation of the van der Waals interaction in the former. It is found that this interaction changes with the type of the stakked π‐systems from repulsive in 6‐d2 to slightly attractive in 16a (see Table 8).
Synthesis of Medium and Large Ring Compounds, XLIII. Synthesis and Isomerization of 8,9‐Dimethyl[6]paracyclophane and Its Bridged Dewar Isomer
Authors: Tochtermann Werner , Rodefeld Lars , Dreeskamp Herbert , Sarge Stefan M.
Published: July 2007

An improved sonochemical procedure for the synthesis of dimethyl [6]paracyclophane‐8,9‐dicarboxylate (2a) on a 10‐g scale is described. The title compound 2d was synthesized from 2a in three steps. Irradiation of 2d yielded the Dewar isomer 3. In solution, the reaction enthalpy for the thermal isomerization of 3 to 2d was determined to be ‐162 ± 16 kJ · mol‐1, while the activation energy for this reaction was found to be 123 ± 12 kJ · mol‐1.
First Synthesis of Enantiomerically Pure Primary Helical Spirocycles Based on the Repetitive Addition of Lithiated Methoxyallene to Chiral 3(2H)‐Dihydrofuranone Derivatives
Authors: Hormuth Stephan , Schade Wolfgang , Reißig Hans‐Ulrich
Published: July 2007

Repetitive additions to chiral 3(2H)‐Dihydrofuranones opened a route to the first enantiomerically pure primary helical spirocyclic compounds. Thus, addition of lithiated methoxyallene 2 to furanone 9 provided adduct 10 with excellent diastereoselectivity. Cyclization with potassium tert‐butoxide in DMSO followed by acid hydrolysis of the resulting enol ether moiety gave spirocyclic furanone 12 in very good overall yield. Repetition of this three‐step sequence converted 12 into 15. For the next series of reactions cerium compound 16 instead of 2 was employed as nucleophile which resulted in reasonable conversion of 15 into adduct 17. By application of the usual methods this compound was transformed into the enantiomerically pure tetracyclic spiro compound 19 in moderate overall yield. Functionalized spiro compounds as described in this paper may serve as enantiomerically pure building blocks in supramolecular chemistry.
Acetogenic Isoquinoline Alkaloids, LXXXII. Biomimetic Total Synthesis of Michellamines A–C
Authors: Bringmann Gerhard , Götz Roland , Harmsen Sven , Holenz Jörg , Walter Rainer
Published: July 2007

The biomimetic first total synthesis of michellamines A, B, and C (1a–c), naturally occurring quateraryl alkaloids with high anti‐HIV activity, is described. Key precursors are the molecular “halves” of michellamines, the antimalarial naphthylisoquinoline alkaloids korupensamine A (2a) and B (2b), which are likewise natural products. These “monomeric” naphthylisoquinoline alkaloids were prepared by Stille‐type intermolecular aryl coupling of the O‐isopropyl‐protected and trialkylstannyl‐activated naphthalene building block 4b with the threefold benzyl‐protected and brominated, enantiomerically pure tetrahydroisoquinoline building block 3a. Ultimate “dimerization” of the protected korupensamines was achieved by biomimetic oxidative phenolic coupling using silver(I) oxide, followed by deprotection to give authentic michellamines. This synthetic route should allow us to easily prepare a broad series of modified analogs of michellamines for extensive structure‐activity investigations.
New Facts on the Stereoselectivity of Monobromocarbenoid Additions to Cyclic Alkenes
Authors: Dehmlow Eckehard V. , Lustinetz Horst
Published: July 2007

The monobromocarbenoid derived from CH2Br2 and NaN(SiMe3)2 gives only endo adducts 4, 5, and 6 with 1,5‐cyclooctadiene, but shows no selectivity with 1,3‐cyclooctadiene. A literature report of a high endo adduct preference of cyclooctene cannot be duplicated, but cyclodecene is converted to 3 with 100% selectivity. Bromocarbenoid adducts 11, 13, and 14 of norbornene and norbornadiene are reported. A possible explanation for the varying selectivities is given.
Solid State and Solution Structures of O‐Alkyl‐ and of O‐Acyl Derivatives of 1‐Hydroxypyridine‐2(1H)‐thione
Authors: Hartung Jens , Hiller Margit , Schwarz Michaela , Svoboda Ingrid , Fuess Hartmut
Published: July 2007

Although Barton's radical precursors, the O‐acyl derivatives of 1‐hydroxypyridine‐2(1H)‐thione 2, have been studied in detail for more than a decade, to date nothing has been reported on the solid state or the solution geometries of these molecules or the analogous oxo derivatives, the pyridones 7, 8. In view of this, selected O‐alkyl and O‐acyl derivatives of pyridinethiones and of 2‐(1H)pyridones have been prepared and investigated by X‐ray diffraction and NMR (COSY, NOE) experiments. The X‐ray data indicate alternating bond lengths in the carbon framework of the heterocycles 2d, 3b, 7b, and 8 and long NO bonds [1.394(4)–1.398(2) Å]. In all the compounds studied, the O‐alkyl and the O‐acyl groups are twisted out of the plane of the heterocycles, which is in accord with the VSEPR concept. Further, the thermal stabilities of thiohydroxamic acid derivatives 2, 3 and of substituted pyridones 7, 8 were studied by differential scanning calorimetry (DSC).
Resonanzenergie von Diradikalen — 1,8‐Naphthoquinodimethan
Authors: Roth Wolfgang R. , Unger Christian , Wasser Thorsten
Published: July 2007

Resonance Energy of Diradicals. — 1,8‐Naphthoquinodimethane

From the racemization of 19c and the temperature and NO dependence of the trapping rate of 20b between 218 and 288°C the energy profile for the equilibrium 19b ⇄ 20b is derived. The singlet‐triplet splitting of the diradical is 2.5 kcal · mol‐1 with the triplet being the ground state. By comparison of the experimental reaction enthalpy with the analogous value for 25, 26 or a hypothetical model reaction with non‐interacting radicals it is shown that the stabilizing interaction of the radicals in the singlet state of 20b is negligible making the stabilization of the triplet equivalent to the singlet‐triplet splitting. By using literature data it is shown by an analogous analysis that the interaction of the radicals in the bisallyl diradical 28 and in the triplet state of the trimethylenmethane derivative 29 is also negligible whereas in the singlet state of 29 the interaction is strongly destabilizing.
Wechselwirkungen in Molekülkristallen, 111. Kristallzüchtung und Strukturbestimmung von Donator/Akzeptor‐Komplexen aus 1,2,4,5‐Tetrakis(alkylthio)benzolen und Brom oder Iod
Authors: Bock Hans , Rauschenbach Andreas , Näther Christian , Kleine Markus , Havlas Zdenek
Published: July 2007

Interactions in Crystals, 111

Part 110: Ref.[1].

. —
Crystallization and Structure Determination of Donor/Acceptor Complexes between 1,2,4,5‐Tetrakis(alkylthio)benzene Derivatives and Bromine or Iodine

Based on preceding cyclovoltammetric and UV/Vis measurements, red crystals of the donor/acceptor complex {1,2,4,5‐tetrakis(ethylthio)benzene…(Br2)2} are grown by using Br2 gasphase diffusion into a CCl4 solution of 1,2,4,5‐tetrakis(ethylthio)benzene. In addition, the corresponding iodine complex {1,2,4,5‐tetrakis(isopropylthio)benzene ⃛(I2)3} is crystallized. The structure determinations prove for the I2 adduct an interesting packing motif, in which two crystallographically independent I2 acceptors bridge each four sulfur donors. The Br2 adduct shows a three‐dimensional network with subunits >S ⃛BrBr ⃛S<, in which the BrBr bond is surprisingly elongated by 13 pm (!) relative to the gasphase electron diffraction value for bromine. — The structure discussion is based on iodine acceptor complexes listed in the Cambridge Structural Database and reveals angular‐dependent iodine coordination vectors to sulfur as well as a correlation between II bond lengths and contact distances S ⃛I. Density functional calculations for the model system (H3C)2S ⃛BrBr ⃛S(CH3)2 with the experimentally determined structural parameters suggest that a charge of ‐0.25 is transferred to the BrBr acceptor molecule, which allows to rationalize its 13‐pm elongation on complexation to {1,2,4,5‐tetrakis(ethylthio)benzene ⃛(Br2)2}.
Antibiotics from Gliding Bacteria, LXXIX. – Chemical Modification of the Antifungal Macrolide Soraphen A1α: Deoxygenation in the South‐East Ring Segment
Authors: Kiffe Michael , Schummer Dietmar , Höfle Gerhard
Published: July 2007

The present paper describes the chemical modification of the antifungal macrolide soraphen A1α (1) by selective removal of oxygen substituents in the south‐east ring segment. In the course of this investigation two key derivatives were prepared: 4‐demethyl‐5‐O‐(4‐methoxybenzyl)‐4‐episoraphen (6) and 3,5‐dideoxy‐4‐oxosoraphen (22). 6 served as precursor for 4‐demethoxysoraphen (19) and 4‐demethoxy‐5‐deoxysoraphen (20). 22 was used for the deoxygenation in positions C‐3, C‐4 and C‐5 and for the synthesis of 3,5‐didesoxysoraphen (24) as well as 4‐demethoxy‐3,5‐dideoxysoraphen (27). The comparison of the antifungicidal activity of these derivatives showed that the OH group in position C‐3 is essential for the biological activity of the soraphens.
A Biphenyl Construction Kit for Modular Chemistry
Authors: Hensel Volker , Schlüter A.‐Dieter
Published: July 2007

The synthesis of a number of telechelic biphenyls with one of the functional groups, B(OH)2, TMS, Br and I, at each ring is presented. These biphenyls constitute a construction kit for modular chemistry using the Suzuki cross‐coupling protocol.
Synthesis of Methyl Derivatives of 4H‐Furo[2,3‐h]quinolin‐4‐one and 5H‐Furo[3,2‐g]quinolin‐5‐one
Authors: Rao Vadapalli S. , Rodighiero Paolo , Chilin Adriana , Castellin Andrea , Manzini Paolo , Guiotto Adriano
Published: July 2007

Synthesis of the linear and angular furoquinolin‐4‐one derivatives 6 and 12 was performed, using nitrobenzofurans 3 and 9 as key intermediates. These compounds were reduced to the corresponding aminobenzofurans 4 and 10, which were condensed in two steps to yield, the linear furoquinolin‐4‐ones 6a,b and the angular ones 12a,b.
No Evidence for Intramolecular Hydrogen Bonds in α‐Fluorocarboxamides
Authors: Michel Dominique , Witschard Martin , Schlosser Manfred
Published: July 2007

α‐Fluorocarboxamides 3a–3e can be prepared by treatment of the corresponding α‐hydroxycarboxamides with diethylaminosulfur trifluoride. The infrared spectra argue strongly against the existence of intramolecular hydrogen bonds between the amino group and the fluorine atom.
Combinatorial Libraries: Studies in Molecular Recognition and the Quest for New Catalysts
Authors: Gennari Cesare , Nestler H. Peter , Piarulli Umberto , Salom Barbara
Published: July 2007

Combinatorial libraries offer a new powerful tool for gathering empirical information about host/guest interactions and for developing catalysts for organic reactions. Combinatorial approaches to molecular recognition are discussed, i.e. screening of libraries of ligands with synthetic receptors and libraries of synthetic receptors with the ligands for which selective binding is desired. Recent achievements in the development of new catalysts for organic synthesis using combinatorial approaches are also reviewed.
Diastereo‐ and Enantioselective Synthesis of Carbocyclic and Heterocyclic β‐Amino Acids by Tandem Aza Michael Addition/Intramolecular Cyclization
Authors: Enders Dieter , Wiedemann Jürgen
Published: July 2007

The stereoselective conjugate addition of (S)‐(–)‐1‐(trimethylsilylamino)‐2‐(methoxymethyl)pyrrolidine (TMS‐SAMP) to ω‐halide‐substituted α,β‐unsaturated esters 1 is utilized to prepare carbocyclic and heterocyclic β‐amino acids 2 and 5 of high diastereo‐ and enantiomeric purity via the corresponding β‐hydrazino esters by selective intramolecular alkylation of the intermediate ester enolate or the hydrazino moiety. The auxiliary is removed by reductive NN bond cleavage. The stereochemistry of the resulting trans‐2‐aminocycloalkanecarboxylic acids (2) and azacycloalk‐2‐ylacetic acid esters (5) is confirmed by NMR spectroscopy and polarimetry. A transition‐state model for the highly diastereoselective conjugate addition of TMS‐SAMP to enoates is presented.
Pyridinium N‐Phenolate Betaine Dyes and Their Application to the Characterization of the Polarity of Solvents, XXII. Syntheses and UV/Vis Spectroscopic Properties of Solvatochromic, Halochromic, and Chiro‐Solvatochromic Pyridinium N‐Phenolate Betaine Dyes with Four Stereogenic Centers
Authors: Reichardt Christian , Blum Andreas , Harms Klaus , Schäfer Gerhard
Published: July 2007

Syntheses (Schemes 1–3), negative solvatochromism (Table 1), cation‐induced negative halochromism (Table 2), and chiro‐solvatochromism (Tables 3 and 4) of the new crown ether‐substituted chiral pyridinium N‐phenolate betaine dyes 18a, b and 28a, b, each posessing four stereogenic centers, are described. The absolute configuration at the four stereogenic centers of the chiral betaine dyes has been confirmed by X‐ray crystal structure analysis of the intermediate phenol 14a (Figure 1). Solutions of the chiral betaine dyes 18a, b and 28a, b, prepared by addition of monochiral amines and amino alcohols to solutions of the salts 17a, b and 27a, b in ethanol, exhibit in some cases small but significant chirosolvatochromic band shifts of up to Δλ = 10–12 nm (Tables 3 and 4), caused by chiral recognition of the monochiral guest molecules.
Galacturonic Acid Derivatives, VIII. Synthesis of N‐(D‐Galacturonoyl) Amino Acids and Dipeptides
Authors: Vogel Christian , Jeschke Udo , Kramer Sven , Ott Andrej‐Jakob
Published: July 2007

D‐Galacturonic acid derivatives, amide‐linked to amino acids or dipeptides, have been synthesized. These glycoconjugates exhibit stability when the uronic acid residue is protected with isopropylidene and acetyl groups or is in its pyranoside form. The formation of the amide or peptide linkages was best achieved by the EDCI/HOBt coupling method; an alternative method employing the 1,2;3,4‐di‐O‐isopropylidene‐α‐D‐galactopyranuronosyl chloride 2 furnished only moderate yields of the conjugates. The use of NMR spectroscopy to detect racemization of the amino acid moiety is also discussed herein.
Structures of Peptaibol Antibiotics Hypomurocin A and B from the Ascomycetous Fungus Hypocrea muroiana hino et katsumoto
Authors: Becker Dieter , Kiess Michael , Brückner Hans
Published: July 2007

From a submerse culture of the fungus Hypocrea muroiana Hino et Katsumoto (Ascomycetes: Hypocreales) two major groups of peptides, designated hypomurocin (HM) A and B, belonging to the peptaibol family, could be characterized. Both groups showed antibiotic activity (Bacillus subtilis) and caused hemolysis of rat erythrocytes, HM A being less active than HM B. Peptides were isolated from the culture broth by chromatography on XAD‐2 adsorber resin, octyl silica, and Sephadex LH 20. HM A and B were separated by preparative TLC, and individual peptides from each microheterogeneous group were isolated by preparative HPLC. Amino acid analysis and sequence determination by fast atom bombardment and electrospray tandem mass spectrometry revealed the composition and structures of six 11‐mer peptides of the HM A group and of six 18‐mer peptides of the HM B group. Positions of isomeric amino acids Leu/Ile and Val/Iva (present in some of the peptides) were determined by methanolytic cleavage of the pure peptides, followed by trifluoroacetylation of the dipeptide methyl esters released and assignment of their structures by gas chromatography‐selected ion monitoring mass spectrometry. As examples, two sequences of HM A and HM B are presented (exchange positions in parentheses). – HM A‐1(2): Ac‐Aib1(D‐Iva1)‐Gln‐Val‐Val‐Aib‐Pro‐Leu‐Leu‐Aib‐Pro‐Leuol11; HMB‐1(2): Ac‐Aib1‐Ser‐Ala‐Leu‐Aib‐Gln‐Aib‐Val‐Aib‐Gly‐Aib‐Pro‐Leu‐Aib‐Aib‐Gln‐Valol18 (Leuol18), (Ac = acetyl, Aib = α‐aminoisobutyric acid, Iva = D‐isovaline, Leuol = L‐leucinol, Valol = L‐valinol).
Diastereo‐ and Enantioselective Synthesis of 4,5,6‐Trisubstituted and 6‐Monosubstituted Piperidin‐2‐ones
Authors: Enders Dieter , Bartzen Dominika
Published: July 2007

A convenient, versatile and highly diastereo‐ and enantioselective synthesis of 4,5,6‐trisubstituted piperidin‐2‐ones 1 in satisfactory overall yields is described. The procedure involves the efficient and highly anti‐diastereo‐ and enantioselective Michael addition of aldehydes to enoates via their lithiated SAMP hydrazones, followed by nucleophilic 1,2‐addition of organometallic reagents to the CN double bond of the corresponding aldehyde SAMP hydrazone‐lithium ester enolate and subsequent lactamisation. In addition, 6‐monosubstituted piperidin‐2‐ones 8 are prepared with enantiomeric excesses of ee = 79–92% via a similar three‐step sequence starting from ethyl 5‐oxovalerate (9).
[2+2] Photocycloadditions of Homobenzvalene
Authors: Christl Manfred , Braun Max
Published: July 2007

The irradiation of methyl phenylglyoxylate, benzil, benzophenone, and 1,4‐benzoquinone in the presence of homobenzvalene (3) gave products of the Paternò‐Büchi reaction, i.e. the oxetane derivatives 4–8, 13 and 14, which contain a tricyclo[4.1.0.02,7]heptane subunit. A regioselectivity was observed in favour of the compounds with the 8‐oxatetracyclo‐[5.2.0.02,4.03,5]nonane skeleton (4, 5, 7, 13). In the case of benzophenone, the cycloaddition was competing with the isomerisation of 3 to cycloheptatriene. No cycloaddition but only isomerisation proceeded with acetophenone and acetone. The irradiation of 1,4‐naphthoquinone and cyclopent‐2‐en‐1‐one in the presence of 3 afforded the cyclobutane derivatives 15 and 17, respectively.
Cycloadditions, 27. The Thermal Rearrangement of the Bicyclo[2.2.2]‐ to Bicyclo[3.2.1]octadiene Moiety in Tricyclic Lactams
Authors: Himbert Gerhard , Diehl Klaus
Published: July 2007

The tricyclic lactams 4a–h, possessing a bicyclo[2.2.2]octadiene moiety, obtained by intramolecular Diels‐Alder reaction of the vinylidene malondiamides 1a–h, generally isomerize in boiling xylene to give the new lactams 7a–h, now bearing a bicyclo[3.2.1]octadiene part. The difference in the rates of the isomerizations 4 → 7 and the results with the nitro ‐ and methoxy‐substituted derivatives 4i–l are in accordance with the proposed intermediate zwitterion 6, which is formed by the migration of one vinyl group from position 1 to position 5 of the lactam moiety.
β‐Peptides: Oligo‐β‐homoalanines – the Amide Analogues of Poly(3‐hydroxybutanoate)
Authors: Matthews Jennifer L. , Overhand Mark , Kühnle Florian N. M. , Ciceri Paola E. , Seebach Dieter
Published: July 2007

The linear oligo‐β‐peptides derived from β‐homoalanine (Hβ‐HAlaOH) have been prepared by Arndt‐Eistert homologation of Boc‐alanine and subsequent peptide coupling procedures. Cyclisation via pentafluorophenyl esters resulted in the formation of the cyclic β‐peptides in remarkably high yields. The X‐ray crystal structure analysis of Boc–(β‐HAla)2–OBn is presented. The cyclic derivatives were found to be highly insoluble (m.p. >300°C with decomposition) and the effect of lithium salts on their solubility, particularly with respect to obtaining NMR data, is discussed. The CD spectra of the cyclo‐β‐tetrapeptides are presented and these give an indication that “nanotube‐like” structures may be present.
Structural Aspects of Cyclopropyl Homoconjugation: Experimental Studies and Ab Initio Calculations
Authors: Haumann Thomas , Benet‐Buchholz Jordi , Klärner Frank‐Gerrit , Boese Roland
Published: July 2007

Low‐temperature crystal structural studies of a series of saturated and unsaturated bicyclo[2.2.1]heptadiene, heptene and heptane compounds with 7‐spirocyclopropyl substitution reveal significant differences in the bond lengths of the three‐membered rings and in the CC single bonds of the bicyclic fragment. A complex interplay of strain and different types of conjugation influence the molecular structure of the bicycloheptadiene derivative1, where the difference in the length of the three‐membered ring bonds is 0.040 Å and all CC single bonds in the bicyclic fragment are lengthened significantly. Ab initio calculations at the HF/6‐31G(d) (to a minor extent) and MP2/6‐31G(d) levels are in good agreement with the experimental data. Calculated charge distributions and dipole moments further support the relevance ofcyclopropyl homoconjugationin the investigated prototype of Walsh and through‐space π‐orbital interaction. Static difference electron density maps have been derived from the experimental data by multipole refinements which showed exocyclic shifts of electron density in the planes of the three‐membered rings and significant bond ellipticities at the CC single bonds in the unsaturated bicyclic units.
4,5‐Diazafluorenylidene: Preparation, Reactivity, Multiplicity, and Selectivity Studies
Authors: Abdel‐Wahab Abdel‐Magd A. , Ismail Mohamed T. , Mohamed Omima S. , Dürr Heinz , Ma Yinmin
Published: July 2007

The chemistry of 4,5‐diazafluorenylidene (3), generated from the diazo compound 3a by photolysis, has been studied with regard to reactivity, multiplicity and selectivity. Reaction of 3 in 2,3‐dimethylbutene gave exclusively ketazine 24. The [1 + 2] cycloaddition with styrenes 5–11 afforded cyclopropanes 16–23 in 25–54% yields and 24 as a side product. In these reactions no diazirine intermediate was involved. Irradiation of 3a in methanol afforded the ether 26 (25% yield). The stereoselectivity of 3 was studied by its addition to (E)‐ and (Z)‐β‐methylstyrene. A mixture of the (E)‐ and (Z)‐cyclopropanes 22 and 23, respectively, was detected. Thus for 3, triplet multiplicity was concluded. The results of competition experiments with singlet/triplet scavengers (methanol/dimethylbutadiene) demonstrated that an equilibrium between singlet and triplet manifold of 3 exists at room temperature. Selectivity studies with carbene 3 were carried out by evaluating the competition experiments of the cycloaddition of 3 with differently substituted styrenes. A plot of the krel values from the competition studies versus Hammett σ constants gave ρ = −0.65 indicating that carbene 3 reacts as an electrophile.
Interaction Between Benzene and Naphthalenophane: In the Gas Phase and the Crystalline Lattice
Authors: Nakamura Yosuke , Suzuki Hideaki , Hayashida Yoshitou , Kudo Takako , Nishimura Jun
Published: July 2007

The interaction between naphthalenophane 1 and another aromatic compound in the gas phase was investigated by molecular orbital calculations, mainly focusing on the arrangement of both aromatic compounds and the effect of the substituents in the benzene ring. The X‐ray crystallographic analysis of some clathrates of 1 with an aromatic solvent was also carried out in order to clarify the relationship between the gas and condensed phases. The most stable arrangement calculated for a complex of 1 and benzene or substituted benzene in the gas phase was found to be the arrangement in which the edges of the two naphthalene rings of 1 are directed to the face of the benzene ring. Such an arrangement was also observed in the clathrate crystals, according to the X‐ray crystallographic analysis. This result suggests that the stable arrangement in the gas phase is probably maintained in solution, leading to the same arrangement in the crystals. The order of stabilization of the clathrates with some substituted benzenes is in agreement with that of the electron‐donating ability of the functional group present in the benzene. A slight difference in the stabilization was observed between the complex with toluene and that with chlorobenzene, and such a difference is considered to affect the inclusion behavior of 1.
Functionalized Derivatives of Benzocrown Ethers, II. Supramolecular Complexes of L‐Amino Acids as Efficient Activators of the Zinc Enzyme Carbonic Anhydrase
Authors: Barboiu Mihai , Supuran Claudiu T. , Scozzafava Andrea , Briganti Fabrizio , Luca Constantin , Popescu Georgeta , Cot Louis , Hovnanian Nadine
Published: July 2007

The preparation of a series of supramolecular complexes of the ammonium salt of 2,3,11,12‐bis[4‐(10‐aminodecylcarbonyl)]benzo‐18‐crown‐6 with different natural and non‐natural amino acids is reported. In all these ditopic supramolecular complexes, with the exception of the histidine derivative, the ammonium moiety of the amino acid is anchored by means of hydrogen bonds within the macrocyclic cavity of the host, whilst the carboxylate moiety interacts with the ammonium group of the derivatized crown ether. The new complexes act as very efficient activators of the zinc enzyme carbonic anhydrase (isozymes I and II).
Pyrolytic Generation and Rearrangement of N‐Substituted 1,2‐Didehydrocarbazoles
Authors: Brown Roger F. C. , Choi Neil , Coulston Karen J. , Eastwood Frank W. , Ercole Frances , Horvath Julianna M. , Mattinson Mark , Mulder Roger J. , Ooi Hua Chee
Published: July 2007

The flash vacuum pyrolysis (900–940°C) of a series of N‐R‐substituted carbazole‐1,2‐dicarboxylic anhydrides (R = methyl, phenyl, o‐tolyl, benzyl, and ethyl) leads to 1,2‐didehydrocarbazoles which undergo ring expansion, cyclisation, and other reactions but which appear not to undergo ring contraction to exocyclic carbenes. Thus the N‐methyl compound 4 gives phenanthridine in 27% yield, the N‐phenyl compound 5 undergoes C‐2′C‐1 cyclisation to indolo[3,2,1‐jk]carbazole 27, and the N‐o‐tolyl compound 6 gives both C‐6′C‐1 cyclisation and 2′‐CH3C‐1 cyclisation. The N‐benzyl compound 7 mainly suffers loss of the benzyl group, but a minor product, benzo[a]carbazole 33, is probably formed by an intramolecular cycloaddition. The N‐ethyl compound 8 forms mainly carbazole and phenanthridine and in addition the minor C‐2′C‐1 cyclisation products pyrrolo[3,2,1‐jk]carbazole 44 and its 4,5‐dihydro derivative 45. The formation of phenanthridine from the N‐methyl anhydride 4 has been investigated by labelling of 4 with 13C at C‐9a.
A Generalized Solvent Acidity Scale: The Solvatochromism of o‐tert‐Butylstilbazolium Betaine Dye and Its Homomorph o,o′‐Di‐tert‐butylstilbazolium Betaine Dye
Authors: Catalán Javier , Díaz Cristina
Published: July 2007

A total of 121 organic solvents were studied and classified by means of the solvatochromic comparison method of Kamlet and Taft, to give a solvent acidity scale for hydrogen‐bond donor solvents based on the parameter SA. This parameter can readily be evaluated from the visible spectrum of a suitable basic probe (o‐tert‐butylstilbazolium betaine dye, TBSB) and its non‐basic homomorph (o,o′‐di‐tert‐butylstilbazolium betaine dye, DTBSB). The proposed scale has many advantages when compared to the more widely used acidity scales such as that based on Gutmann's acceptor number (AN) and the Taft‐Kamlet α scale. Whilst data for the proposed scale are derived from electronic transitions only, they do provide an accurate description for solvent acidity effects in spectroscopy and other chemical areas, including thermodynamics and kinetics.
Synthesis of 21‐(3‐Methylbutyl)cholest‐5‐ene‐3β,3′,25‐triol and 21‐(2‐Methylpropoxy)cholest‐5‐ene‐2′,3β,25‐triol, the First “Double Side Chain” Cholesterol Analogues
Authors: Kurek‐Tyrlik Alicja , Makaeva Fliur Z. , Wicha Jerzy , Calverley Martin J.
Published: July 2007

The 21‐(3‐hydroxy‐3‐methylbutyl)‐ and 21‐(2‐hydroxy‐2‐methylpropoxy)cholestane derivatives 3 and 5, formally double chain hybrid (20R)‐ and (20S)‐cholesterol analogues, were synthesized. The C‐22 to C‐27 section of the 25‐hydroxycholestane side chain was established by stereoselective alkylation with 5‐bromo‐2‐methyl‐2‐(triethylsilyl)oxypentane of the pregnanoic ester 8, derived from 3β‐acetoxyandrost‐5‐en‐17‐one (7). Reduction of the ester 9 to the 21‐alcohol 10 permitted elaboration of a second hydroxylated side chain, either via the tosylate 11 by alkynation/hydrogenation (yielding intermediate 13) or by alkylation of 10 with bromoacetate (yielding 14) followed by reaction with methyl magnesium bromide.
Synthesis of Optically Active 2‐siloxycyclopropanecarboxylates by Asymmetric Catalysis, V. Baeyer–Villiger Oxidations of γ‐Oxo Esters – Determination of the Absolute Configurations of Methyl 2‐Siloxycyclopropanecarboxylates – Interpretation of the Enantioselective Cyclopropanations of Silyl Enol Ethers
Authors: Reißig Hans‐Ulrich , Schumacher Ralf , Ferse Dirk
Published: July 2007

Racemic and enantiomerically enriched methyl 2‐siloxycyclopropanecarboxylates 1 have been ring‐opened to furnish γ‐oxo esters 2. Depending on the electronic properties of substituents, these could be transformed into either succinate derivatives 3 or 3‐oxybutanoates 4 by Baeyer‐Villiger oxidation. By comparison with known reference compounds the absolute configurations of 3a and 4d, and hence those of their cyclopropane precursors, could be determined. Further literature data on the optical rotations of related cyclopropanes have been collected and compared. A mechanistic interpretation of the asymmetric cyclopropanation of silyl enol ethers based on Pfaltz's model is suggested.
Highly Stereoselective Synthesis of the 1‐O‐Acylglycosyl Ester of Diclofenac via Glycosyl Phosphorothioates, ‐Selenoates and ‐Dithioates as Glycosyl Donors
Authors: Borowiecka Joanna
Published: July 2007

Stereoselective glycosylation of o‐(2,6‐dichloroanilino)phenylacetic acid (Diclofenac, 1), as a free carboxylic acid with glycosylthio (2a–c), ‐dithio (3a–e) and ‐selenophosphates (4a–c) as glycosyl donors is reported. The reactions were carried out in aprotic solvents, in the presence of silver carbonate as a leaving group activator. 1‐O‐Acyl sugars 7a–e, new derivatives of Diclofenac, were obtained in high yields as stable, crystalline compounds.
Efficient Enantioselective Synthesis of Chiral Precursors for the Preparation of Vitamin E
Authors: Tietze Lutz F. , Görlitzer Jochen
Published: July 2007

Enantioselective bishydroxylation of the protected hydroxymethyl enynes 7a–d and 8a, b, which are easily obtained from commercially available 5 and 6, gave the triol derivatives 9a–d and 11a, b in good yields and moderate to high enantiomeric excess. Palladium‐catalyzed coupling of 9a–d and 11a, b with the iodoarene 13 led to the desired precursors for the vitamin E synthesis ent‐3a–d and 15a, b.