bluuebunny/crossref_metadata_2025 huggingface dataset:
Ternary liquid equilibria system: Acetic acid + water + toluene
Authors: Dakshinamurty P. , Subrahmanyam V. , Rao M. Narsimha
Published: June 2010

Phase equilibrium data for the ternary liquid‐liquid system acetic acid + water + toluene were determined at 30, 40 and 60 °C adopting the method of Dakshinamurty et al. The phase equilibrium data at 30 °C and the tie line data at 30, 40 and 60 °C obtained by the above method were compared with the data obtained by the method of Othmer, White and Trueger and a fair agreement between the data sets was obtained. The tie line data were well correlated by the methods of Hand and of Othmer and Tobias. At the three temperatures the solute (acetic acid) is in greater weight fraction in the aqueous phase. The distribution was shown to be temperature dependent.
Intramolecular Carbene Addition to a Triple Bond – Matrix Photochemistry of α‐Diazo‐2‐ethynylacetophenone
Authors: Komnick Peter , Sander Wolfram
Published: June 2010

The irradiation (λ =403 nm) of α‐diazo‐2‐ethynylacetophenone (1 a) in solid argon at 10 K leads to (2‐ethynylphenyl)ketene (11) as the major product. A minor product is benzo‐4‐oxo‐2,5‐cyclohexadienylidene (6) which on 475‐nm irradiation reversibly rearranges to cycloprop[a]inden‐6(6aH)‐one (5a). This demonstrates that the intramolecular addition of the carbene center to the double bond can compete with the Wolff rearrangement.
Synthesis of Enantiomerically Pure Hydroxyethylporphyrins and Their Transformation into Optically Active Chlorin Derivatives
Authors: Kusch Dirk , Montforts Franz‐Peter
Published: June 2010

The oxazaborolidine (9)‐catalyzed reduction of acetylporphyrins (4) led to enantiomerically pure hydroxyethylporphyrins (5), which were transformed into optically active chlorin derivatives (7 and 8) upon reaction by N,N‐dimethylacetamide dimethyl acetal followed by hydrogenation. The absolute configuration of the synthesized chlorins was elucidated by means of their CD spectra.
Ring‐Opening Reactions of 3,5‐Bis(methylthio)‐1,2‐dithiolium Salts with Cyclopentadienides
Authors: Hartke Klaus , Popp Xue‐Ping
Published: June 2010

4‐Aryl‐substituted 3,5‐bis(methylthio)‐1,2‐dithiolium salts such as 1a react with metal cyclopentadienides 4 (M+ =Tl, Li) mainly by cleavage of the S–S bond. A subsequent intramolecular Diels‐Alder addition of the ring‐opened structures 5/6 gives the tricyclic compounds 7a and 8a, b. Intramolecular condensation of 5 or 6 yields the cyclopenta[b]thiopyran 11a. With the 4‐unsubstituted 3,5‐bis(methylthio)‐1,2‐dithiolium salt 1b the intramolecular Diels‐Alder adducts 8c, d and 9a, 10a were isolated. 4‐Alkyl‐substituted 1,3‐bis(methylthio)‐1,2‐dithiolium salts such as 1c react with thallium cyclopentadienides 4 mainly by substitution at C‐3 leading to the formation of the 2,3‐dithiafulvalenes 12a, b. The reaction of these salts with lithium cyclopentadienides leads to S–S bond cleavage followed by an intramolecular condensation affording the cyclopenta[b]thiopyran 11b.
Polycyclic Aromatic Alkaloids, XI A Convenient Formal Total Synthesis of the Cytotoxic Marine Alkaloid Amphimedine
Authors: Bracher Franz , Papke Thomas
Published: June 2010

The pyridylbenzo[c][2,7]naphthyridinone 2, a central intermediate for the total synthesis of amphimedine (1), was prepared in two steps from the readily available quinoline 3. Palladium‐catalyzed cross‐coupling of 3 with 4‐(trimethylstannyl)pyridine gave the biarene 4, which could be converted to the target compound 2 by using a one‐pot anellation method.
Enkastines: Amadori Products with a Specific Inhibiting Action against Endopeptidase – 24.11 – from Streptomyces albus and by Synthesis
Authors: Vértesy László , Fehlhaber Hans‐Wolfram , Kogler Herbert , Schindler Peter W.
Published: June 2010

Target‐oriented screening led to the detection of specific inhibitors of endopeptidase – EC 3.4.24.11 – (enkephalinase) in cultures of Streptomyces albus, ATCC 21 838. Isolation was performed by successive chromatographic methods and yielded enkastines in amounts of about 2 mg from 2000 kg of culture broth. Amino acid analysis, proton‐ and carbon‐NMR spectroscopy, mass spectrometry, and chemical degradation suggested the structure of the three most prominent enkastines to be N‐(1‐deoxyfructos‐1‐yl)‐isoleucyl‐aspartate (1), N‐(1‐deoxyfructos‐1‐yl)‐valyl‐aspartate (2), and N‐(1‐deoxyfructos‐1‐yl)‐valyl‐glutamate (3). This structural hypothesis was confirmed by chemical synthesis of the compounds according to the Amadori reaction of glucose with the corresponding dipeptides. The products turned out to be identical with the isolated material with respect to their NMR fingerprint (1H and 13C) and their biological properties. Enkastines are potent inhibitors of the endopeptidase 24.11. with IC50 of 1.8 × 10−9 M (1), 6.3 × 10−9 M (2) and 3 × 10−8 M (3). In contrast to phosphoramidon, a well‐known inhibitor of the enkephalinase, enkastines exhibit no activity against thermolysin. Kinetic studies characterize enkastine activity as competitively slow and tightly binding to endopeptidase – EC 3.4.24.11.
3‐Alkylidene‐2‐azetidinethiones: Useful Intermediates for the Synthesis of 3‐Substituted 2‐Azetidinethiones
Authors: Nieschalk Jens , Spanka Carsten , Schaumann Ernst
Published: June 2010

3‐Lithiated 2‐azetidinethiones 1 were allowed to react with carbonyl compounds to give 3‐(1‐hydroxyalkyl)‐2‐azetidinethiones 3, 4 which were converted into α,β‐unsaturated β‐thiolactams 7, 8, 10 by elimination procedures. Alternatively, the title compounds were prepared by Peterson olefination of 3‐trimethylsilyl‐2‐azetidinethiones 9. Reactions of 7, 8, 10 with thiophenol or sodium diethyl malonate provided the Michael adducts 11. E/Z Photoisomerization of 7, 8 by visible light was observed. On deprotonation, 7a, 8a underwent allyl rearrangement to 13.
Sterically Congested Molecules, 16 A Convenient Synthesis of Di‐tert‐butyl Ketone via its Imine, 2,2,4,4‐tetramethyl‐3‐pentanimine
Authors: Knorr Rudolf , Donhärl Angelika , Hennig Karsten‐Olaf
Published: June 2010

2,2,4,4‐Tetramethyl‐3‐pentanimine (3) is efficiently prepared by a Barbier‐type reaction of pivalonitrile (1) with an excess of tert‐butyl chloride (2) and metallic lithium in ether. Its purification by extraction into aqueous acid and slow hydrolysis permit an inexpensive and very simple production of di‐tert‐butyl ketone (4).
Chemoenzymatic Synthesis of (R)‐(+)‐Patulolide A, a Macrolide Antibiotic Isolated from Penicillium urticae
Authors: Kitamura Masaya , Nagaoka Hiroyuki , Naoshima Yoshinobu , Kamezawa Makoto , Tachibana Hojun , Ohtani Takehiko
Published: June 2010

(R)‐(+)‐Patulolide A [(R)‐1] was synthesized with an enantiomeric purity of almost 100% e.e. by a two‐step lipase‐catalyzed enantioselective hydrolysis of racemic thioketal acetate (±)‐11.
Bimolecular Formation of Radicals by Hydrogen Transfer, 10. On the Mechanism of Quinone Dehydrogenations
Authors: Höfler Christoph , Rüchardt Christoph
Published: June 2010

The mechanistic alternatives in the literature for quinone dehydrogenations of hydroaromatic to aromatic hydrocarbons are reviewed. In a kinetic study of the reaction of DDQ 16 with 9,10‐dihydroanthracene (13) or xanthene (17) small solvent effects and small rate differences between 13 and 17 (Table 1) but large kinetic isotope effects kH/kD were observed. In addition, intermediate 9‐hydroanthryl radical 20b and 9‐xanthyl radicals 19b were trapped by the addition of nitrosobenzene to the dehydrogenation reaction mixtures as shown by the ESR spectra of the spin adducts 22 and 23. These results are better explained by an initial H atom transfer step (retrodisproportionation, RD) than by direct hydride transfer (DHT). Possible consequences for biochemical hydrogen transfer processes are addressed briefly.
Synthesis of a New Chiral Peptide Analogue of DNA Using Ornithine Subunits and Solid‐phase Peptide Synthesis Methodologies
Authors: Lioy Eduardo , Kessler Horst
Published: June 2010

In this paper we describe the synthesis of chiral peptide nucleic acids (PNAs) 1–3 using SPPS methodologies. Starting material for the monomer units was the commercially available amino acid ornithine. l‐ or D‐ornithine and the nucleobase thymine were linked by a carboxymethylene spacer giving the chiral monomers l‐7 and D‐7. The SPPS was performed according to the Fmoc strategy.
A Concise and Stereoselective Synthesis of threo‐γ‐Hydroxy‐l‐β‐lysine Lactone
Authors: Misiti Domenico , Zappia Giovanni , Monache Giuliano Delle
Published: June 2010

A stereoselective synthesis of threo‐γ‐hydroxy‐β‐l‐lysine lactone is reported. The threo‐amino alcohol functionality is introduced by iodine‐mediated cyclocarbamation of the electron poor allylamine 6. The D‐phenylalanine was used as starting material as synthetic equivalent to D‐aspartic acid.
Preparation and Structure Proof of the Four Isomeric Dicyanocobyrinic Acid Hexamethyl Ester Monoamides Carrying the Amide Group on a Propionic Acid Side Chain
Authors: Ernst Ludger , Maag Hans
Published: June 2010

Selective ammonolysis of dicyano‐cobalt(III)cobyrinic acid heptamethyl ester (cobester, 2) furnishes the four isomeric hexamethyl ester monoamides 2b, 2d, 2e, 2f carrying the amide function on one of the propionic acid side chains. The isomers were separated by liquid‐liquid chromatography and their structures determined by a comparison of their 13C‐NMR spectra with the spectrum of 2. Amide 2f served as the link between synthetic and authentic vitamin B12 derived material in the total synthesis of vitamin B12.
Organophosphorus Compounds, 111 Phospha Ene Reactions of a P‐Chlorophosphaalkene as a Versatile and Powerful Enophile Building Block
Authors: Mackewitz Thomas W. , Regitz Manfred
Published: June 2010

[Bis(trimethylsilyl)methylene]chlorophosphane (1) has proved to act as an extremely reactive enophile in phospha ene reactions with all‐carbon enes of differing constitutions and so provides a general approach to β,γ‐unsaturated chlorophosphanes. Thus, for example, 1 reacts even at room temperature or slightly elevated temperatures with the terminal alkenes 6a–c, the methylenecycloalkanes 6d, e, h, and the cycloalkenes 6f, g to furnish the corresponding allyl‐substituted chlorophosphanes 7a–h. Dimethylallene (8) undergoes addition to 1 to yield the phosphanyl‐substituted buta‐1,3‐diene 9 whereas allene (10) itself reacts with 1 by way of a previously unknown phospha ene reaction to give the propynyl‐substituted chlorophosphane 11. By contrast, the (chlorophosphanyl)allene 13 results from the reaction of 1 with but‐2‐yne (12). All of these group transfer reactions proceed chemo‐ and regioselectively with P/C bond formation. The constitutions of all the phospha ene adducts, which were isolated in satisfactory to good yields after purification by distillation, were unequivocally confirmed by analytical and spectroscopic methods.
Synthesis and Stereoselective CC Bond‐forming Reactions of Peptide Aldehydes
Authors: Reetz Manfred T. , Griebenow Nils
Published: June 2010

The reaction of the activated form of N‐protected amino acids 6 and 10 or peptides 14 and 18 with chiral amino alcohols derived from the corresponding α‐amino acids affords peptide alcohols which can be oxidized under Swern conditions to produce the corresponding peptide aldehydes 9, 12, 16 and 20. The rational synthesis of diastereomeric di‐ and tripeptide aldehydes, e.g., (S,S)‐ or (R,S)‐dipeptides as well as (S,S,S)‐ or (R,S,S)‐tripeptides is possible by proper choice of the respective building blocks [(S)‐ versus (R)‐amino acids]. The compounds can be prepared without any undesired α‐epimerization. However, the long‐term configurational stability depends upon the configuration at the remote stereogenic center, e.g., (R,S)‐dipeptide aldehydes epimerize faster than the (S,S) diastereomers. Di‐ and tripeptide aldehydes 9, 12, 16 and 20 undergo chelation‐controlled Grignard‐type additions with Me2CuLi that involve little or no undesired α‐epimerization. The (S,S)‐ and (R,S)‐dipeptide aldehydes 9 and 12 undergo chelation‐controlled pinacol reactions induced by the low‐valent vanadium reagent [V2Cl3(THF)6]2[Zn2Cl6]. The major products in both cases are the corresponding C2‐symmetric diols 33 and 36, respectively, which are of interest as potential HIV‐protease inhibitors. The degree of stereoselectivity is significantly higher in the case of the (S,S)‐dipeptide aldehydes relative to the (R,S) analogs, an observation which can be explained on the basis of three‐point binding of the peptides to vanadium.
Influence of Substituents on the Rotational Energy Barrier of Axially Chiral Biphenyls, II
Authors: Wolf Christian , Hochmuth Detlev H. , A. König Wilfried , Roussel Christian
Published: June 2010

The influence of substituents on the rotational energy barrier of a series of 2,2′‐bis(trifluoromethyl)‐ and 2,2′‐diisopropylbiphenyl derivatives with various substitution patterns was investigated by dynamic gas chromatography (DGC) with selectively modified cyclodextrins and by high‐performance liquid chromatography (HPLC) on microcrystalline cellulose triacetate combined with polarimetry. Investigation of the steric effect of substituents was possible by gradually increasing the bulkiness of substituents in the ortho positions of 2,2′‐disubstituted biphenyls and determination of the corresponding energy barriers. The buttressing effect of alkyl groups adjacent to the ortho substituents is discussed. Comparison of the energy barriers of 2,2′‐bis(trifluoromethyl)biphenyl (1) with its derivatives possessing alkyl groups in positions 3 and 5, respectively, allows a discrimination between the electronic and steric contributions of the meta substituents and thus the determination of the influence on the energy barrier. The electronic effect on the rate of rotation, i.e. the rate of enantiomerization, of axially chiral biphenyls bearing substituents in the para positions depends on the aromatic system to which they are attached. Electron‐donating groups decrease the rotational energy barrier of 2,2′‐bis(trifluoromethyl)biphenyl derivatives but increase the barrier of 2,2′‐diisopropylbiphenyl derivatives. Electron‐accepting groups exhibit the opposite behavior. The unexpected effects in the case of para‐substituted 2,2′‐diisopropylbiphenyl derivatives are possibly related to C–H/π interactions.
Synthesis of Liposomal Phospholipid‐(N4‐palmitoyl‐1‐β‐D‐arabinofuranosylcytosine) Conjugates and Evaluation of Their Cytostatic Activity against l1210 Murine Leukemia
Authors: Schott Herbert , Schwendener Reto A.
Published: June 2010

N4‐Palmitoyl‐araC, a prodrug of the cytostatic compound 1‐β‐D‐arabinofuranosylcytosine (araC), was linked by means of the triester method to the phospholipids (2‐chlorophenyl) (1,2‐di‐O‐palmitoylglyceryl) phosphate, (2‐chlorophenyl) (1,2‐di‐O‐octadecylglyceryl) phosphate and (2‐chlorophenyl) (1‐O‐octadecyl‐2‐O‐palmitoylglyceryl) phosphate. In the first step of these gram‐scale syntheses phospholipid‐(N4‐palmitoyl‐araC) conjugates were obtained the linkage of which was accomplished via a triester group. In the second step the final condensates were obtained through transformation of the triester into a diester linkage by removal of the 2‐chlorophenyl group. The cytostatic activity of these compounds which form stable liposomal preparations together with matrix lipids was evaluated according to the L1210 mouse leukemia model. The conjugates containing a triester linkage were shown to be ineffective, whereas those with a diester linkage display a significantly higher antitumor activity as compared to N4‐palmitoyl‐araC and araC. With the diester 6a–8a 80–100% of the treated animals were cured at a total dose of 200 μmol/kg, whereas with araC given at a fourfold higher concentration none of the treated mice survived.
Wechselwirkungen in Kristallen, 95 Formyl(2‐pyridyl)amin: Monomer in der Gasphase, dimer im Kristall
Authors: Bock Hans , Van Tran T. H. , Solouki Bahman , Schödel Holger , Artus Georg , Herdtweck Eberhardt , Herrmann Wolfgang A.
Published: June 2010

Interactions in Crystals, 95. – Formyl(2‐pyridyl)amine: Monomeric in the Gasphase, Dimeric in the Crystal

The title molecule [HC]4NC–NH–CHO (2), an α‐aminopyridine derivative, forms a dimer via an hydrogen bridge pair (NH…N)2 in the crystal. In the gasphase, however, it remains a monomer as proven by the well‐resolved He(I) photoelectron spectrum and its Koopman's assignment, IEnv = ‐ϵJSCF, of the radical cation state pattern. The enthalpy difference for dimerization is approximated by AM1 calculations to be rather small. Nevertheless, on crystallization either from an aprotic solution or by sublimation through the gasphase, due to the cooperative effect and to the density‐dependent increase in lattice energy, a self‐organization to the dimer is observed.
Synthesis of 5‐/10‐Membered Ring Analogues of the Dienediyne Core of Neocarzinostatine Chromophore by Palladium(0)‐Mediated Ring‐Closure Reaction
Authors: Suffert Jean , Abraham Estelle , Raeppel Stéphane , Brückner Reinhard
Published: June 2010

The new dienediynes 5, 6, and 7 were synthesised from a monoprotected diyne and an already described bis(enol triflate) 4 derived from formylcyclopentanone. When 5 and 6 were subjected to nucleophilic attack by a thiol, cycloaromatisation occurred, and the phenanthrenes 23a and 23b were obtained in 30 and 42% yield, respectively.
Synthesis of 6‐/10‐Membered Ring Analogs of the Dienediyne Core of the Neocarzinostatin Chromophore by Palladium(0)‐Mediated Ring‐Closure Reactions
Authors: Brickmann Kay , Hambloch Frank , Suffert Jean , Brückner Reinhard
Published: June 2010

A strategy for the synthesis of the benzo‐annulated bicyclic dienediyne analogs 46 and 48 of the DNA‐cleaving natural product neocarzinostatin chromophore was developed. 2‐Formylcyclohexanone (9) was converted stereoselectively first into the mono(enol triflate) Z‐11 and thereafter into the bis(enol triflate) Z‐2. The isomeric triflates E‐11 and E‐2 were prepared to facilitate correct E,Z assignments. The C≡C bonds of the target dienediynes 46 and 48 were introduced with the aid of the unsymmetrical bisalkynes 17 and 16, respectively. However, the latters furnished the formers not by reactions with the monotriflate Z‐11 (Schemes 4, 7, 10) but only by reactions with the bistriflate Z‐2. The success of this approach is due to a regioselective Csp2/Csp monocoupling which unites the reaction partners and to another Pd‐catalyzed Csp2/Csp coupling which furnished the 6‐/10‐membered ring dienediyne 46 (Scheme 13) and its isomer 48 (Scheme 14). Starting from ortho‐bromobenzaldehyde and cyclohexanone these syntheses required a total of 9 and 10 steps, respectively, the longest linear sequence comprising 6 steps.
The First Syntheses of 6‐/10‐Membered Ring Analogs and of a 6‐/11‐Membered Ring Analog of the Dienediyne Core of the Neocarzinostatin Chromophore by Ring‐Closure According to the Nozaki‐Hiyama Reaction
Authors: Eckhardt Matthias , Brückner Reinhard
Published: June 2010

The Z‐configurated dienediyne aldehydes 11, 13, 19, and 20 were prepared as pure isomers by Pd(0)‐catalyzed C,C couplings between appropriate terminal alkynes and the bis‐(enol trifluoromethanesulfonate) 5 or its mono(enol trifluoro‐methanesulfonate) derivative 18. Irrespective whether these aldehydes contained a C≡CH or a C≡CSiMe3 moiety, they cyclized with low efficiency (11, 13, 19) or not at all (20) to the corresponding 6‐/10‐membered ring dienediynes (compounds 10, 8, 21, and 22, respectively). However, the C≡CI analogs 6 and 26 of these aldehydes furnished the desired 6‐/10‐membered ring dienediynes 8 and 22 by Nozaki‐Hiyama reactions; these cyclizations were complete and essentially clean conversions, provided an excess of CrCl2 and a stoichiometric amount of NiCl2 were used. However, since dienediynes 8 and 22 decompose very readily they were isolated only in 26 and 53% yield. Similar ring‐closure reactions of the iodinated alkinyl aldehydes 36a and b — which were obtained from the same mono(enol trifluoromethanesulfonate) 18 and the alkynes 32a and b, respectively, in four steps (Scheme 7) — furnished the 6‐/10‐membered ring dienediyne 38 (51% yield) and the 6‐/11‐membered ring dienediyne 39 (54% yield). They are the most stable dienediyne analogs of the neocarzinostatin chromophore which we have so far synthesized. They were oxidized to the corresponding dienediyne ketones 40 and 41 (Scheme 8). The latter compounds cycloaromatized in the presence of methyl thioglycolate and 1,4‐cyclohexadiene at 35–37°C to give the tetrasubstituted benzenes 47 and 48 as the only and as the main product, respectively (Scheme 9).
Experimental and Theoretical Studies of the Internal Stereodifferentiation Occurring During the Lithiation of β‐Stereogenic Alkyl Carbamates. Kinetic Resolutions by (‐)‐Sparteine‐Mediated Deprotonation
Authors: Haller Jan , Hense Thomas , Hoppe Dieter
Published: June 2010

The deprotonation of β‐stereogenic alkyl carbamates 8 with sec‐butyllithium/TMEDA proceeds kinetically controlled with differentiation between the diastereotopic protons at the α‐methylene group. The lithium intermediates 9A and 9B are trapped by electrophiles to give carboxylic acid esters 10A/B and stannanes 11A/B, 13A/B. The diastereomeric ratio of A to B is independent of the electrophile. The highest efficiency is achieved with β‐aryl‐β‐alkyl‐substituted starting compounds 8d–f. The trends in the experimentally observed diastereoselectivities are reflected by the results of semiempirical PM3 calculations on the transition states of the deprotonation reaction. — As a result of double stereodifferentiation, application of the chiral base sec‐butyllithium/(‐)‐sparteine gives rise to efficient kinetic resolution of racemic alkyl carbamates.
Pheromone Synthesis, CLXXIV. Synthesis of (5R,11S)‐5,11‐Dimethylheptadecane and (S)‐2,5‐Dimethylheptadecane, the Major and the Minor Components of the Sex Pheromone of the Geometrid Moth, Lambdina fiscellaria lugubrosa
Authors: Mori Kenji , Horikiri Hiromasa
Published: June 2010

(5R,11S)‐5,11‐Dimethylheptadecane (1), the major component of the female‐produced sex pheromone of the western hemlock looper (Lambdina fiscellaria lugubrosa), was synthesized by starting from the enantiomers of methyl 3‐hydroxy‐2‐methylpropanoate (3). (S)‐2,5‐Dimethylheptadecane (2), the minor and synergistic component of the pheromone, was also synthesized by starting from (S)‐citronellol (4).
Photoinduced Electron Transfer (PET) Cyclization and Photooxygenation of 2,6‐Diaryl‐1,6‐heptadienes and 2,7‐Diaryl‐1,7‐octadienes
Authors: Griesbeck Axel G. , Sadlek Oliver , Polborn Kurt
Published: June 2010

The 2,6‐diaryl‐substituted 1,6‐heptadienes 3a–c and the 2,7‐diaryl‐substituted 1,7‐octadienes 4a–b were cleanly converted into the corresponding anellated cyclobutanes 5 and 6, resp., when irradiated under photoelectron‐transfer conditions (9,10‐dicyanoanthracene in acetonitrile). Only for 4c did the rearranged compound 7c become the dominant photoproduct. Oxygen trapping experiments with formation of endoperoxides 8, 9 were successful in the case of the electron‐rich substrates 3b, c and 4c.
Novel Tetrathiafulvalenes Based on Macrocyclic Thioethers
Authors: Wagner Michael , Zeltner Stephan , Olk Ruth‐Maria
Published: June 2010

Macrocyclic polythioethers (7–10, 17) and the oxothioether 21 were synthesized by starting with the key compound 4,5‐bis(benzoylthio)‐1,3‐dithiole‐2‐thione (1). Intramolecular phosphite coupling reactions yielded symmetrically and unsymmetrically substituted tetrathiafulvalenes 11–14 and 22, respectively.
Synthesis and Crystal Structure of a Bis[6.3.3]propellane
Authors: Jamrozik Janusz , Żeslawski Wojeciech , Grochowski Jacek , Serda Pawel , Dauter Zbigniew
Published: June 2010

The bis[6.3.3]propellane 6 derivative of 2,2′,6,6′‐tetramethylbiphenyl was, in the final stage, synthesized by dehydration, of octaalcohol 5. X‐ray structure analysis revealed the highly symmetric shape of the molecule and disordered oxygen atoms in the tetrahydrofuran rings. The dihedral angle between LSQ phenyl planes is 62.6(1)°.
Secondary Metabolites by Chemical Screening, 29.
Authors: Göhrt Axel , Grabley Susanne , Thiericke Ralf , Zeeck Axel
Published: June 2010

Novel pyranacetals, named agistatines A, B, D, and E (1 to 4), were discovered by a chemical screening in the culture broth of the fungus FH‐A 6239. The structures were established by detailed spectroscopic investigations and confirmed by X‐ray analysis of agistatine B (2), 4‐O‐(2‐bromobenzoyl)dihydroagistatine A (6), 4‐O‐(2‐bromobenzoyl)agistatine B (7), and agistatine E (4) leading to the stereochemical information. The described secondary metabolites exhibit unusual bicyclic (1 and 3) and tricyclic (2 and 4) structures with a characteristic ketal moiety at C‐2 (except 3). The instability of the main fermentation product agistatine E (4) is caused by an additional hemiketal located at the adjacent C‐‐8a.
Pseudosugars, 37. Preparation of Versatile Intermediates for Ether‐Linked 5a‐Carba Oligosaccharides: Synthesis of 5a‐Carba‐β‐D‐GlcpNAc‐(1→4)‐D‐Manp
Authors: Ogawa Seiichiro , Hirai Keisuke , Ohno Masatsugu , Furuya Takashi , Sasaki Shin‐Ichi , Tsunoda Hidetoshi
Published: June 2010

Coupling of 1,2‐anhydro‐3‐O‐benzyl‐4,6‐O‐benzylidene‐5a‐carba‐β‐D‐mannopyranose (3) with 1,6‐anhydro‐2,3‐O‐isopropylidene‐β‐D‐mannopyranose (4) afforded a 5a′‐carba disaccharide derivative linked by an ether bridge with α‐manno configuration. This compound 5 was transformed into three stereoisomers in regard to the configurations at C‐1′ and C‐2′. Thus, the free 2′‐hydroxyl group was oxidized, and the resulting ketone 8 was isomerized at C‐1′ to 11 by treatment with potassium tert‐butoxide. Reduction of the ketones 8 and 11 with l‐selectride afforded selectively the synthetic useful intermediate ether‐linked 5a′‐carba disaccharides 9, 12, and 14 with α‐gluco, β‐gluco, and β‐manno configurations, respectively. 5a‐Carba sugar analog 2 of biologically interesting disaccharide β‐D‐GlcpNAc‐(1→4)‐D‐Manp (1) was synthesized.
Synthesis of 1,4‐Oxathiocines and Thiopyrans by the Reaction of 2‐Amino‐4,5‐dihydro‐3‐thiophenecarbonitriles with Ethyl Diazoacetoacetate
Authors: Yamagata Kenji , Akizuki Keiko , Yamazaki Motoyoshi
Published: June 2010

The reaction of 4,5‐dihydro‐2‐(4‐morpholinyl)‐ or ‐2‐(1‐piperidinyl)‐ or ‐2‐(1‐pyrrolidinyl)‐3‐thiophenecarbonitriles 1a–i with ethyl diazoacetoacetate in the presence of rhodium (II) acetate dimer gave the corresponding ethyl 1,4‐oxathiocine‐3‐carboxylates 2a–f, h and acetyl(dihydro‐1‐thiophenylio)‐(ethoxycarbonyl)methanides 3a, b. Compounds 2a–f, h and 3a, b were heated at 140°C to give the corresponding ethyl thiopyran‐6‐carboxylates 4a–i in moderate to good yields.
Reactions of Cyclic Diynes with Acceptor‐Substituted Alkynes: Syntheses of Doubly Bridged Dewar Benzenes
Authors: Gleiter Rolf , Ohlbach Frank , Oeser Thomas , Irngartinger Hermann
Published: June 2010

The reaction of the AlCl3 complex of cyclic diynes (mainly a 14‐membered ring) with dimethyl acetylenedicarboxylate (DMAD) or bis(tert‐butylsulfonyl)acetylene (BTSA) and related compounds was investigated. The reaction of the AlCl3 complex of cyclotetradeca‐1,8‐diyne (1, n = 5) with DMAD affords in 60% yield two isomers in a ratio of 7:3. The isomers were identified as the 1,4‐ and 2,3‐bridged Dewar benzene derivative A and the 1,2‐ and 3,4‐bridged Dewar benzene derivative B. Acetylenes with sterically more demanding groups such as BTSA or bis(diphenylphosphanyl)acetylene P,P′‐dioxide (BDPA) yield only the isomer A. The X‐ray structures of the cycloadduct between 1 (n = 5 and 6) and BTSA, as well as of 2,3‐bis(tert‐butylsulfonyl)‐1,4,5,6‐tetramethylbicyclo[2.2.0]hexa‐2,5‐diene (31) are described. The mechanism of the cycloadditions is discussed.
A Convenient Synthesis of S‐[(2R)‐2‐Acetamido‐3‐(hexadecyloxy)propyl] 2‐(Trimethylammonio)ethyl Thiophosphate, a New Amido‐Thiophosphate Analog of PAF
Authors: Młotkowska Barbara , Pościk Adam
Published: June 2010

The naturally configurated S‐[(2R)‐2‐acetamido‐3‐(hexadecyloxy)propyl] 2‐(trimethylammonio)ethyl thiophosphate (5), a new amido‐thiophosphate analog of the Platelet Activating Factor (PAF), was obtained in a seven‐step reaction sequence by starting from N‐acetyl‐l‐cysteine (6).
Phosphanalkylene, 55 Reaktionen von Alkylidentriphenylphosphoranen mit nitrierenden Reagentien
Authors: Bestmann Hans Jürgen , Kamberger Werner , Röder Thomas , Zimmermann Reiner
Published: June 2010

Phosphane Alkylenes, 55.— Reactions of Alkylidenetriphenylphosphoranes with Nitrating Reagents

The reaction of phosphonium ylides 1 with N2O4 (2) is strongly influenced by the natur of the substituents of the starting ylide. Formation of α‐nitro‐α‐nitrosoalkanoates 8, nitrolic acid 11, and nitriles 13 was realized. Nitration at the phenyl group of benzylidenephosphoranes 24 or at the γ‐position of allylidenephosphoranes 30 accompanied by transylidation and oxidation processes leads to the formation of nitro‐substituted ylides 26 and 32, respectively. Strongly basic ylides and ethyl nitrate (34) undergo complex reactions as is shown in the formation of the aziridinyl‐substituted ylide 40 from ethylidenetriphenylphosphorane (9) and 34. Allylidenetriphenylphosphoranes 41 are nitrated by ethyl nitrate (34) at the γ‐position affording (γ‐nitroallylidene)triphenylphosphoranes 43, from which nitro dienes 45 are available. In the reaction of 1‐(dimethylamino)‐2‐nitroethylene (46) with phosphonium ylides nitro‐vinylation of the starting ylide takes place.
Synthesis of Mono‐ and Sesquiterpenoids, XXV. Synthesis of (6R*,7R*)‐7‐Hydroxy‐6,11‐cyclofarnes‐3(15)‐en‐2‐one, the Racemate of the Antibacterial Sesquiterpene from Premna oligotricha, and Its (6R*,7S*) Isomer
Authors: Yajima Arata , Takikawa Hirosato , Mori Kenji
Published: June 2010

The structure of the antibacterial sesquiterpene from Premna oligotricha was shown to be not 1 but 2 (relative stereochemistry) by the unambiguous synthesis of both (±)‐1 and (±)‐2.
Geometries of Three‐Membered Rings in Triangulanes and Spirocyclopropanated Bicyclopropylidenes: Experimental Studies and a General Bond Increment Scheme
Authors: Boese Roland , Haumann Thomas , Jemmis Eluvathingal D. , Kiran B. , Kozhushkov Sergei , de Meijere Armin
Published: June 2010

Crystal structural studies of several linear and branched triangulanes, together with spiro‐cyclopropanated bicyclopropylidenes, by X‐ray diffraction reveal significant differences between proximal and distal bond lengths in the three‐membered rings. Combined with previously published structural data, these results allowed us to elaborate a general additivity scheme describing the geometry of such hydrocarbons. The π donor spirocyclopropane and a double bond shorten the proximal bonds by 0.0234 and 0.0327 Å and lengthen the distal bonds by 0.0227 and 0.0327 Å with respect to the unperturbed value of 1.5008 Å. The results of these calculations were compared with those obtained by semiempirical and ab initio methods and explained qualitatively by using the Fragment Molecular Orbital (FMO) approach.
Enol Cation Radicals in Solution, 9. Synthesis and One‐Electron Oxidation Chemistry of Novel, Stable Conjugated Dienols and Yne‐Enols
Authors: Schmittel Michael , Langels Anja
Published: June 2010

For the first time stable enols containing the 1,3‐dien‐2‐ol and the yne‐enol functionalities were synthesized, characterized and investigated by cyclic voltammetry. According to the spectral data and AM1 calculations full conjugation between the enol moiety and the vinyl or alkynyl substituents was attained. One‐electron oxidation of enols E1–5 with tris(1,10‐phenanthroline)iron(III) hexafluorophosphate provided in most cases the novel benzofurans B that were isolated and characterized. The mechanism of the benzofuran formation is discussed.
The First Tetrathio‐Substituted Cyclobutane‐1,2,3,4‐tetracarbonitrile — A New Highly Substituted Cyclobutane
Authors: Spannenberg Anke , Holdt Hans‐Jürgen , Teller Joachim , Praefcke Klaus , Kopf Jürgen
Published: June 2010

The first tetrathio‐substituted cyclobutane‐1,2,3,4‐tetracarbonitrile 9 was obtained by an intramolecular photoinduced [2 + 2] cycloaddition reaction of the 14‐membered macrocyclic tetrathioether 7 containing two 1,2‐dicyano‐1,2‐dithioethene units in dichloromethane in 73% yield.
Stereoelectronic Effects and Chiral Recognition, II. Kinetic and Thermodynamic Control in the Formation of Chiral Thioacetals and Chiral Thioethers
Authors: Noe Christian R. , Knollmiiller Max , Ziebarth‐Schroth Irene , Letschnig Marion
Published: June 2010

The ratio of diastereomers obtained from chiral thiols 2 was shown to be time‐dependent both in thioacetal formation with lactol 1 (diastereomers 3/4) and in 1,4‐addition to nitrostyrene 5 (diastereomers 6/7, 8/9). An interpretation based on stereoelectronic effects is presented to explain the similarity of the reaction pathways in both reactions.
Diastereo‐ and Enantioselective Diels‐Alder Reactions of 2‐Amino‐1,3‐dienes
Authors: Enders Dieter , Meyer Oliver
Published: June 2010

The employment of 2‐amino substituted 1,3‐dienes in cycloaddition reactions has recently extended the scope of Diels‐Alder methodologies. In this review, the preparation of a variety of 2‐amino‐1,3‐dienes is presented, and the use of these cross conjugated enamines in normal as well as hetero Diels‐Alder reactions is depicted. Diastereo‐ and enantioselective variations show new aspects for the preparation of cyclic carbonyl compounds in a highly stereoselective fashion. Further cyclisation reactions e.g. cyclopropanation reactions are also considered in this account.
Photochemical Fragmentation of Unsubstituted Tetrazole, 1,2,3‐Triazole, and 1,2,4‐Triazole: First Matrix‐Spectroscopic Identification of Nitrilimine HCNNH
Authors: Maier Günther , Eckwert Jürgen , Bothur Axel , Reisenauer Hans Peter , Schmidt Christiane
Published: June 2010

Equilibria between the tautomers of heterocyclic azoles like 1, 2, and 4 have been studied many times. We here show that the application of density functional methods in combination with matrix IR spectroscopy is a useful tool for determining which protomer is preferred in rare gas matrices and thus also can be assumed to dominate in the gas phase. Photolysis of tetrazole (4) in cryogenic matrices allows the IR‐spectroscopic identification of a new CH2N2 isomer, the long soughtafter nitrilimine HCNNH (6). Flash pyrolysis of 4 also yielded nitrilimine. Upon irradiation this species is converted to a second, previously unknown “isomer”, an HCN/NH complex 13. Nitrilimine (6) can also be generated by photolyzing 1,2,3‐ (1) and 1,2,4‐triazole (2) in Ar matrices. The complex photochemistry of all three heterocyclic precursor compounds was unveiled. Our findings were supported by isotopic substitution experiments and by high‐level ab initio calculations. Moreover, the IR bands of iminocyanide HNCN were tentatively assigned. This radical has up to now not been observed in a matrix.
Synthetic Microbiol Chemistry, XXIX!. Synthesis of Both the Enantiomers of Incrustoporin, an Antibiotic from Incrustoporia carneola
Authors: Yajima Arata , Mori Kenji
Published: June 2010

Both the enantiomers of incrustoporin (2‐p‐tolyl‐2‐hexen‐4‐olide, 1) were synthesized by starting from methyl p‐tolylacetate (2) and (S)‐1,2‐epoxybutane (3). The naturally occurring compound 1 was shown to possess the R configuration.
The First Asymmetric Carroll Rearrangement Diastereo‐ and Enantioselective Synthesis of Polyfunctional Ketones with Vicinal Quaternary and Tertiary Stereogenic Centers
Authors: Enders Dieter , Knopp Monika , Runsink Jan , Raabe Gerhard
Published: June 2010

The first asymmetric Carroll rearrangement opens up an efficient access to highly functionalised ketones 4 and 7 with vicinal quaternary and tertiary stereogenic centres of excellent diastereo‐ and enantiomeric purity (de =89–96%, ee =82 to >98%) by using the SAMP/RAMP hydrazone methodology. Starting from hydrazones (S)‐2, we describe a dianionic and a Lewis acid‐mediated variant of the [3.3]‐sigmatropic Carroll rearrangement. The relative and absolute configuration of the new stereogenic centres created by C–C bond formation were assigned by X‐ray crystallographic analysis of the hydrazones 3h and 3j.
Selective Acylations of Multifunctional Nucleophiles, Including Carbohydrates and Nucleosides, with Intermediates Generated by Wolff Rearrangement of Amino Acid Derived Diazo Ketones: Preparation of β‐Amino Acid Derivatives
Authors: Guibourdenche Christel , Podlech Joachim , Seebach Dieter
Published: June 2010

The diazo ketones derived from Z‐ and Boc‐protected alanine, valine, and alanyl‐alanine (1–5) were decomposed by catalytic amounts of silver benzoate/Et3N in the presence of polyfunctional nucleophiles such as 3‐methyl‐1,3‐butanediol, 2‐aminoethanol, carbohydrates (xylofuranose and sucrose) and nucleosides (thymidine, adenosine derivatives). In many cases, products of β‐amino acylations are formed (6–14, 15b, 17–19, 21, 23, 24) with surprising functional group selectivities. The scope and limitations of the method are described.
Restricted Flexibility of the Glycosidic Linkage in α(1→3)‐L‐Digitoxosides as Determined by NMR Spectroscopy and MMC Calculations
Authors: Köpper Sabine , Meyer Bernd
Published: June 2010

The preferred conformations of nine protected α(1→3)‐linked digitoxoside trisaccharides 1–9, α‐L‐Dig‐(1–3)‐α‐L‐Dig‐(1–3)‐α‐L‐Dig (C–B–A), constituents of tetronolide antibiotics, were determined by a combination of 300‐MHz NMR spectroscopy and potential energy calculations using the GEGOP programme. Chemical shift differences and nuclear Overhauser enhancements indicated some unusual short distances between not directly bound digitoxose residues A and C. Thus, the glycosidic linkages of the nine α(1→3)‐linked digitoxosides have a fairly high rigidity as indicated by the relatively large absolute NOE (≈︁3%) from 1C‐H to 5A‐H. MMC simulations of the conformational flexibility resulted in preferred conformations of the glycosidic linkages of ΦC,B/ΨC,B ≈︁ 70°/40° and ΦB,A/ΨB,A ≈︁ 65°/50° with ranges of 40°/50° and 50°/60°. By energy minimisations a second minimum was identified for the B–A glycosidic linkage at ΦB,A/ΨB,A ≈︁ 0°/40° with an energy higher than 2.0 kcal/mol to the main minimum. The MMC‐derived ensemble‐averaged NOEs that were obtained by sampling the main minimum agree well with the experimental values, whereas NOEs derived from MMC runs that stayed at the local minima are not in accord with experimental values. The MMC simulations failed to give transitions between the two minima presumably because of a high energy barrier between the minima. All nine trisaccharides seem to adopt a well‐defined conformation characterised by a narrow distribution in the conformational space that is located in the region of the global minimum.
Intermolecular Hetero Diels‐Alder Reactions of Enamino Ketones with Highly Substituted Vinyl Ethers Effect of High Pressure on the Kinetics and Diastereoselectivity
Authors: Buback Michael , Kuchta Gabriele , Niklaus Anja , Henrich Marielouise , Rothert Iris , Tietze Lutz F.
Published: June 2010

The hetero Diels‐Alder reactions of enamino ketones 1 and 2 with the vinyl ethers 3–5a are studied in dichloromethane solution under high pressures up to 5 kbar. The kinetics is measured by on‐line FT‐IR spectroscopy to 3 kbar. The cycloaddition reactions of enamino ketones 1 and 2 with vinyl ethers 3 and 4 yield the diastereomeric dihydropyrans 7a–d and 8a–d, respectively, whereas in the cycloaddition of enamino ketone 1 to vinyl ether 5a the constitutional isomers 9 and 11 are formed. The unexpected reaction of 1 with 5a to give the spiro compound 9 is explained by isomerisation of 5a to 5b under the reaction conditions. The kinetics of the reactions is discussed in terms of both overall and individual rate coefficients, activation energies, and activation volumes
Structures and Properties of Tris(donor)‐Tris(acceptor)‐Substituted Benzenes, 8!!. On the Balance of Steric, Electronic and Hydrogen Bond Effects in 1,3,5‐Tris(amino)‐2,4,6‐Tris(acceptor)‐Substituted Benzenes
Authors: Jens Wolff J. , Gredel Frank , Hillenbrand Daniela , Irngartinger Hermann
Published: June 2010

The conformational properties of triamino‐substituted 1,3,5‐trinitrobenzenes were studied by X‐ray crystallography, dynamic NMR spectroscopy, and semiempirical calculations. As amino substituents all possible combinations of a dialkyl‐, a monoalkylamino, and an amino group were used. All derivatives have radialene‐like structures with the central six‐membered ring distorted from planarity. The geometric form of the latter was linked with the electronic organization of the π system. Despite the presence of up to six intramolecular hydrogen bonds, semi‐empirical calculations reproduce experimental geometries quite well.
Base‐Catalyzed Dehalogenation of 2,6‐Di‐tert‐butyl‐4‐iodophenol Formation and Structure of a New Oxocyclohexadienylidene Bisphenol
Authors: Reischl Gerald , Rieker Anton , Maichle‐Mössmer Cäcilia , Abram Sonja
Published: June 2010

2,6‐Di‐tert‐butyl‐4‐iodophenol (1) does not react to the keto carbene 4 under strongly basic conditions and exclusion of oxygen, in contrast to a report in the literature. In the presence of oxygen, however, oxidation takes place. Reaction times and product pattern strongly depend on the concentration of O2. Besides biphenyl 2, diphenoquinone 3, and quinone 5, a new (oxocyclohexadienylidene)bisphenol 6 was isolated, and its molecular structure was determined by X‐ray crystallography. A radical mechanism is suggested for the formation of the above products from 1. The bisphenol 6 was also synthesized by thermolysis of the quinone diazide 11 in the presence of 3.
Chemistry with Roataxanes: Intra‐ and Intermolecularly Covalently Linked Rotaxanes
Authors: Jäger Ralf , Händel Mirko , Harren Jörg , Vögtle Fritz , Rissanen Kari
Published: June 2010

The direct introduction of sulfonamide units (cf.9) into carboxamide‐based rotaxanes allows us to intramolecularly bridge the “wheel” and the “axle” of such species for the first time as is shown by the bridged bissulfonamide rotaxane11. Due to its stronger acidity the SO2‐NHproton can be selectively abstracted by mild bases even in the presence of CO.NHand then be substituted by treatment with suitable iodo compounds. This leads intramolecularly to11(71% yield) and intermolecularly to bis[2]rotaxane16(76% yield). The iodo‐substituted rotaxane15isolated as a remarkably stable byproduct offers a new synthetic potential demonstrated by the preparation of16.
(–)‐Methyl Cucurbate and (–)‐Methyl Jasmonate by Kinetic Resolution
Authors: Borm Claudia , Winterfeldt Ekkehard
Published: June 2010

The kinetic resolution of a malonate‐substituted cyclopentenone gave rise to the formation of an enantiopure Diels‐Alder adduct which was converted into methyl dehydrocucurbate 2 by diastereoselective alkylation with (Z)‐1‐bromo‐2‐pentene and subsequent borohydride reduction. Selective hydrogenation of 2 with a palladium/calcium carbonate catalyst proved to be a reliable route to (–)‐methyl cucurbate (1) the oxidation of which with pyridinium chlorochromate and subsequent treatment with acid afforded (–)‐methyl jasmonate (9).
ortho‐Azobenzenophanes: Photochemical and Thermal Reactions of [2,2][2,2′]Azobenzenophane
Authors: Tauer Erich , Machinek Reinhard
Published: June 2010

The cyclic azo compounds 6 and 7 were synthesized. The chemical properties of 6 were investigated. Irradiation of the trans,trans form 6t,t leads to isomerization to the trans,cis form 6t,c and to the cis,cis form 6c,c. Compounds 6t,c and 6c,c can be isolated. However, thermally, 6t,c and 6c,c react slowly back to 6t,t. All attempts to convert 6 by light into the tetrazetidine 10 have been unsuccessful until now. In boiling toluene 6 undergoes an interesting rearrangement, namely a ring contraction, during which an azo group is cleaved with formation of an indole ring and a primary amino group.
Synthesis of Novel C‐Methylflavones
Authors: Hauteville Marcelle , Gaillard Pascale , Duclos Marie‐Christine , Kaouadji Mourad
Published: June 2010

If the Baker‐Venkataraman rearrangement of C‐methylphloracetophenone triaroyl esters is carried out in DMSO with powdered NaOH, the result greatly depends on the substitution pattern both of the phloracetophenone moiety possessing either one or two C‐methyl groups and of the aroyl parts bearing a conjugated methoxy group (or not such a group) with respect to the carbonyl group. With benzoyl, 4‐methoxybenzoyl or 3,4‐dimethoxybenzoyl as aroyl group the 3,5‐dimethylphloracetophenone triaroyl esters 10a–c directly yield the corresponding unsubstituted ring B or 4′‐methoxy‐ and 3′,4′‐dimethoxy‐substituted 5,7‐dihydroxy‐6,8‐dimethylflavones 11a–c. In contrast, the 3‐methylphloracetophenone triaroyl esters 3a–c react quite differently, depending on the aroyl substitution pattern. Thus, the triester 3a containing benzoyl groups gives the hemiketal Wessely‐Moser isomers 5a, 5a′ whereas the triesters 3b and 3c containing 4‐methoxy‐ or 3,4‐dimethoxybenzoyl groups are converted into compounds existing as two equilibria of two β‐diketo and two β‐keto enol tautomers. Finally, dehydration of each mixture furnishes solely the corresponding unsubstituted ring B or 4′‐methoxy‐ and 3′,4′‐dimethoxy‐substituted 5,7‐dihydroxy‐6‐methylflavones 8a–c. Methylation of 11c affords 7‐O‐methyl and 5,7‐di‐O‐methyl derivatives 12a and b.
Alkylations of Chiral Imidazolidinones Derived from Di‐ and Triglycine and Attempts at Cyclisations to Give Cycloisodityrosines
Authors: Bezencon Olivier , Seebach Dieter
Published: June 2010

Di‐ and triglycine derivatives (1–5) containing a 2‐tert‐butyl‐1,3‐imidazolidin‐4‐one moiety were prepared in rac. and enantiopure forms. By deprotonations with LiNR2 these imidazolidinones were converted to Li, Li2, and Li3 derivatives (H‐N) and the latter alkylated, preferably with the more reactive electrophiles (MeI, benzylic and allylic bromides). The diastereoselectivity at the endocyclic (imidazolidinone) position is always very high (>95:5), while it varies with respect to the newly formed stereocentres at the exocyclic positions (2:1 to >95:5). Three dozens of new di‐ and triglycine derivatives were thus prepared and fully characterised. Cyclisation attempts with seven different diaryl ethers (23, 29, 32, 35, 39, 44, 45), which are potential precursors of cycloisodityrosines, failed. The configurations of the products were assigned by X‐ray structure analysis (29, 40, 53), NMR analysis, and hydrolysis to the amino acid components, followed by GC analysis.
Preparation of 12‐ and 16‐Membered Macrolactones (Oligolides) from (S)‐Malic Acid – Low Molecular‐Mass Analogs of the Biopolymer Poly[(S)‐Malic Acid] (PMA)
Authors: Hoffmann Torsten , Seebach Dieter
Published: June 2010

As model compounds of uniform composition for the biopolymer PMA, 12‐ and 16‐membered oligolides derived from malic acid by esterification between the carboxylic acid and the β‐hydroxy groups were prepared (Schemes 1 and 2). A reduced form of the triolide derivatives 2, 4, the tris(hydroxymethyl) triolide 10, was also synthesized (Scheme 3). The macrocyclic compounds were isolated in up to 60% yield and fully characterized. The water‐soluble tri‐ and tetracarboxylic acids of this type, thus available for the first time, will be studied as potential binders to polycationic biomolecules.
New Synthetic Routes to 2‐Fluoro‐2‐phenylalkanoic Acids
Authors: Goj Olav , Haufe Günter
Published: June 2010

2‐Fluoro‐2‐phenylalkanoic acids 2 are obtained by oxidation of the corresponding β‐fluoro‐β‐phenyl alcohols 6. These compounds are shown to be accessible by two alternative pathways, either by bromo fluorination of α‐alkyl styrenes 3, subsequent bromine‐by‐acetate replacement in the bromo fluorides 4 and hydrolysis of the acetates 5 or by a BF3 · OEt2 catalyzed ring opening of corresponding styrene oxides 8 with triethylamine tris(hydrofluoride).