bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of carbon‐bridged N‐acetyl‐c‐lactosamine and derivatives
Authors: Eisele Thomas , Ishida Hideharu , Hummel Gerd , Schmidt Richard R.
Published: July 2007

4‐C‐Formyl‐2‐azidoglucopyranoside 12a, required for N‐acetyl‐C‐lactosamine synthesis as electrophile, was obtained from thexyldimethylsilyl 2‐azido‐2‐deoxy‐glucopyranoside 3 via readily available 4‐O‐unprotected 6a and then 4‐C‐methylene derivative 8a in overall seven steps. Alternatively, regioselective silylation of 3 with tert‐butyldimethylsilyl chloride gave 4‐O‐unprotected 6b which was transformed by a similar reaction sequence into 12a. In order to circumvent a Wittig reaction, 6a was transformed into triflate 13 the reaction of which with 4‐C‐cyano derivative 14 followed by reduction with DIBAH and base‐catalyzed isomerization also afforded 12a. Reaction of 12a with 1‐C‐lithiated 2‐phenylsul‐finyl‐D‐galactal 15 as nucleophile furnished C‐disaccharide intermediates 16a and 16b as diastereoisomers. Ensuing removal of the phenylsulfinyl group with Raney nickel and diastereospecific 2b‐hydrogen and 3b‐hydroxy transfer afforded β(1→4)‐connected N‐acetyl‐C‐lactosamines 19a and 19b; their structures were deduced from derivatives 20a, b and 21a, b on the basis of 1H‐NMR data. Hydrogenolytic O‐debenzylation of 19b afforded hydroxymethylene‐bridged N‐acetyl‐C‐lactosamine 2b′.
Trapping reactions of sulfenes generated from sulfonic acid derivatives and bases, 2. [4 + 2] cycloadditions of 1,2,3,4,5‐pentamethylcyclopentadiene and 1,3‐diphenylbenzo[c]furan with sulfenes
Authors: Opitz Günter , Deißler Michael , Rieth Karlheinz , Wegner Ralf , Irngartinger Hermann , Nuber Bernhard
Published: July 2007

Sulfenes 2a‐o, generated in situ from sulfonyl chlorides and Et3N, are trapped by 1,2,3,4,5‐pentamethylcyclopentadiene (6) to give [4 + 2] cycloadducts 8a‐o containing the 7‐methyl group in anti position. With mesylsulfene (7), formed in situ from mesyl chloride/Et3N in MeCN solution, the [4 + 2] cycloaddition to endo/exo‐ 9 (X‐ray analyses) is accompanied by a [2 + 2] cycloaddition to 10 (X‐ray analysis). (+)‐10‐Camphorsulfonyl chloride/Et3N afforded only two (and no more) diastereomeric [4 + 2] cycloadducts (endo/exo‐8d). Et3N can be replaced by Me3N, N,N,N′,N′‐tetramethylnaphthalene‐ 1,8‐diamine or NaH, the sulfonyl chlorides to a limited extent by sulfonyl fluorides, sulfonic acid anhydrides or aryl esters. Formation of 8p from 6 and dichloromethanesulfonyl chloride requires NaH or AgNO3 or tertiary amine/AgNO3. N‐(2‐Methyl‐1‐propenyl)pyrrolidine is more reactive than 6 in trapping sulfene 2a. 6, however, is a more efficient sulfene scavenger than 1,3‐diphenylbenzo[c]furan (19), which reacts with sulfene 2d by [4 + 2] cycloaddition and SO2 extrusion to give ketone 21d in only 18% yield.
Naphthothiete und ihre Anwendung in der Heterocyclen‐Synthese
Authors: Mayer Axel , Rumpf Norbert , Meier Herbert
Published: July 2007

Naphtothietes and Their Application to the Synthesis of Heterocycles

The three isomeric naphthothietes 5, 11, and 16 were prepared according to the reaction sequences shown in Schemes 1–3. The final step was in each case a flash vacuum pyrolysis (FVP) of the corresponding mercaptonaphthalenemethanol 4, 9, and 15, respectively. The thiete rings in 5 and 11 can be opened by gentle heating; the ring opening of the isomer 16 possesses a much higher activation barrier. A MNDO calculation of the ΔHf values of 5, 11, and 16 and the open isomers 5′, 11′, and 16′ provides an explanation for the different behavior. Photochemical ring opening represents a useful alternative. The reaction Schemes 4, 6, and 7 reveal the synthetic potential of the naphtho‐condensed thietes. Cycloaddition reactions with CC, CO, or CN double bonds lead into the series of differently condensed thiopyrans 17, 18, 24, 25, 26, 3,1‐oxathiine 19 and 1,3‐thiazines 20, 21.
A convenient synthesis of 5‐amino‐6‐aryl‐3‐(β‐D‐galacto‐ or ‐β‐D‐glucopyranosyl)tetrahydro‐2‐thioxo‐4H‐1,3‐thiazin‐4‐ones
Authors: Yadav Lal Dhar S. , Yadav Danveer S.
Published: July 2007

The Michael addition of the sulfur nucleophiles N‐(β‐D‐galacto‐ or ‐β‐D‐glucopyranosyl)dithiocarbamic acid (2a, b) to 4‐arylidene‐5‐oxazolones (3a‐d) followed by ring transformation of the resultant Michael adducts 4a‐h and hydrolysis yielded new 5‐amino‐6‐aryl‐3‐(β‐D‐galacto‐ or ‐β‐D‐glucopy‐ranosyl)‐tetrahydro‐2‐thioxo‐4H‐1,3‐thiazin‐4‐ones 6a‐h in a one‐pot procedure.
Polyether Catalysis of Ester Aminolysis – A Computational and Experimental Study
Authors: Zipse Hendrik , Wang Li‐Hsing , Houk Kendall N.
Published: July 2007

Model systems for the reaction of amines with esters were investigated with ab initio methods. Ammonia and methylamine were used as models for primary amines, and formic acid, methyl acetate, phenyl acetate, and p‐nitrophenyl acetate were chosen to represent typical esters. Geometry optimizations were performed for all systems with the HF/6–31G** method, and relative energies were evaluated by using MP2/6–31G** single‐point energies. The lowest barriers are found for the reaction of methylamine with p‐nitrophenyl acetate. Reaction occurs in this case according to a direct displacement pathway, in which all bond formation and breaking occurs in a single step. Complexation of the transition structures by dimethyl ether or dimethoxyethane leads to much the same changes as observed for variation of the leaving group. Based on the ab initio data a force field for the calculation of transition state‐catalyst complexation was developed. This force field as well as ground state complexation energies were employed to predict catalytic activities for a number of polyethers, polyalcohols, and pyrans, which in part, were also investigated experimentally.
Synthesis of (1S,2R,5R)‐2‐Ethyl‐1,5‐dimethyl‐6,8‐dioxabicyclo[3.2.1]octane, the Aggregation Pheromone of Male Beech Bark Beetles, Taphrorychus bicolor (Col., Scol.)
Authors: Francke Wittko , Schröder Frank , Kohnle Ulrich , Simon Matthias
Published: July 2007

The absolute configuration of the new bicyclic acetal 2‐ethyl‐1,5‐dimethyl‐6,8‐dioxabicyclo[3.2.1]octane (1), identified as an aggregation pheromone of males of the beech bark beetle, Taphrorychus bicolor, was determined by unambiguous synthesis and NMR experiments. The syntheses of the racemates of both diastereomers and of optically pure samples are described. The natural product proved to show (1S,2R,5R) configuration.
Ring Expansion of Heterocyclic Ketene N,X‐Acetals and 2‐Alkylidenedihydroindoles with Methanesulphonyl Azide by [3 + 2] Cycloaddition and Subsequent Extrusion of Molecular Nitrogen
Authors: Quast Helmut , Ivanova Svetlana , Peters Eva‐Maria , Peters Karl , Schnering Hans Georg Von
Published: July 2007

Methanesulphonyl azide (2) reacts readily with isolated cyclic ketene N,X‐acetals of type 1, viz. 10a, d, 15b, d, and 22a–c, or those that are generated in situ by deprotonation of the corresponding 2‐alkylbenzazolium tetrafluoroborates, i.e. 14a → 15a, 14b → 15b, and 18 → 19. Ring‐expanded products are formed by extrusion of molecular nitrogen from intermediate labile [3 + 2] cycloadducts 3 with concomitant 1,2‐shift of N (route A1 → 12, 24) or X (route A2 → 16, 20, 21). In addition, 3 may undergo [3 + 2] cycloreversion into N‐sulphonylimine 5 and diazoalkane 6 (route B → 13, 17, 25). The configurations of the cyclic N‐sulphonylamidines 16b and 21b, the N‐sulphonylimine 24 and the N‐sulphonylamine 27 are elucidated by means of X‐ray diffraction analyses. The ratio of the (useful) ring‐expansion reactions vs. the unwanted formation of 5 + 6 is hardly influenced by the solvent employed and temperature of the experiment but strongly by the nature of the potential migrating atom and the substituents at the α‐carbon atom.
Optically Active 5‐(Hydroxyalkyl)‐ and 5‐(Aminoalkyl)pyrazolidin‐3‐ones by Ring‐Chain Transformation of α,β‐Unsaturated Lactones or Lactams with Hydrazines
Authors: Bohrisch Jörg , Faltz Heike , Pätzel Michael , Liebscher Jürgen
Published: July 2007

α,β‐Unsaturated lactones or lactams 1 react with hydrazines 2 via Michael‐like addition and subsequent ring transformation by nucleophilic attack of the hitherto unchanged hydrazine nitrogen atom at the carbonyl carbon atom. The addition is highly trans‐stereoselective, thus affording optically active hydroxylalkyl‐ or aminoalkylpyrazolidin‐3‐ones 4 and 6. These pyrazolidin‐3‐ones are further transformed to tosylated, acetylated or silylated derivatives 9 or react with benzaldehyde to give the azomethine imine 10.
What Governs the Stereochemistry of the SN2′ Reaction?
Authors: Borrmann Tobias , Stohrer Wolf‐Dieter
Published: July 2007

Ab initio calculations of negatively charged symmetrical and unsymmetrical transition states of the SN2′ reaction indicate that due to electronic reasons and particularly Coulomb interactions the anti transition state is generally more stable than the syn transition state. The experimentally often observed syn preference results mainly from the interaction with a polar solvent and/or the gegenion, which gives rise to higher stabilization of the syn transition state than of the anti transition state.
Glycosyl Imidates, 76. Synthesis of Aryl C‐Glycosides of Glucosamine
Authors: Castro‐Palomino Julio C. , Schmidt Richard R.
Published: July 2007

The N‐tetrachlorophthalimido‐protected glucosamine donor 2 reacts with electron‐rich phenol ethers 3a–c to afford aryl C‐glycosides 4a–c. The N‐tetrachlorophthaloyl group could be readily removed by sodium borohydride treatment and then phthalide formation or by treatment with ethylenediamine, respectively. The resulting product was subjected to reaction with acetic anhydride in pyridine to afford N,O‐acetylated compounds 5a–c. After treatment with enthylenediamine also the N,O‐unprotected compounds could be obtained as shown for 6c.
On Some Italicene Derivatives
Authors: Weyerstahl Peter , Marschall Helga , Christiansen Christian , Seelmann Ingo
Published: July 2007

Oxidation of the tricyclic sesquiterpene hydrocarbon italicene (1a) or its 10‐epimer 1b (isolated previously from Helichrysum oil) with SeO2 yielded mixtures of italicene‐5‐one (3a), italicen‐15‐al (4a), italicen‐5‐ol (9a) and italicen‐15‐ol (10a) or their 10‐epimers 3b, 4b, 9b, 10b, whereas commercial α‐copaene (6) reacted only to give a mixture of α‐copaen‐15‐al (7) and α‐copaen‐15‐ol (8). Jones oxidation of the allyl alcohols 9a or 9b afforded the pure ketones 3a or 3b MnO2 oxidation of the alcohols 10a or 10b furnished the aldehydes 4a or 4b. – Surprisingly, the italicene epoxides 2a or 2b rearranged with diluted HCl to the italicene ethers (epoxyacorenes) 5a or 5b, which previously were isolated from Lantana and Helichrysum oil. – The odor of 3a, 3b, 4a, 4b and 5a was evaluated.
Antibiotics from Gliding Bacteria, LXXVIII. Ripostatin A, B, and C: Isolation and Structure and Structure Elucidation of Novel Metabolites from Sorangium cellulosum
Authors: Augustiniak Hermann , Höfle Gerhard , Irschik Herbert , Reichenbach Hans
Published: July 2007

Three closely related new metabolites named ripostatins were isolated from the myxobacterium Sorangium cellulosum and their structures elucidated by spectroscopic methods. Two of them, ripostatin A (1a, b) and B (2a), are 14‐membered macrolides with an acetic acid and a phenylalkyl side chain, whereas the third metabolite ripostatin C (3a) is an acyclic derivative of ripostatin A. By application of the method of Helmchen the absolute stereochemistry could be determined as (11R,13R) for ripostatin A, 11R,13S,15R for ripostatin B and 11S for ripostatin C. The polyketide origin of A was revealed by feeding experiments with 13C‐labeled precursors demonstrating the incorporation of one molecule of phenylacetic acid derived from phenylalanine, one propionate unit, and ten acetate units.
1,4‐Didehydronaphthalin
Authors: Roth Wolfgang R. , Wasser Thorsten , Zimmermann Heiko , Hopf Henning , Werner Christian
Published: July 2007

1,4‐Didehydronaphthalene

The energy profile of the Bergman equilibrium o‐diethinyl‐benzene (1 · 1,4‐didehydronaphthalene (2) has been established from the temperature and NO dependence of the trapping rate of the diradicals 2 which leads to a heat of formation for 2 of ΔHf0 = 152.9 · 1.4 kcal · mol−1. Activation parameters for the hydrogen abstraction of 2 and 1,4‐didehydrobenzene (5) have been derived from the rate of the naphthalene and benzene formation, when 1 and cis‐3‐hexene‐1,5‐diyne (4) are heated in the presence of methanol, toluene, and 1,4‐cyclohexadiene.
Stereoselective Synthesis of Alcohols, L. Stereoselective Synthesis of a C‐15/C‐27 Segment of the Venturicidines
Authors: Hoffmann Reinhard W. , Rolle Ulrike , Göttlich Richard
Published: July 2007

Chain extension of an aldehyde by two “propionate” units has been attained by stereoselective allylboration with the chiral 1‐methylbutenyl boronate 3 to give, e.g., the homoallylic alcohol 6, followed by a regioselective hydroboration/carbonylation procedure to give, e.g., the epimeric aldehydes 8. The latter were converted into the lactols 10, which equilibrated to the desired epimer. The lactols could again be subjected to an allylboration reaction, initiating a second round of the chain extension protocol. This technique has been used to synthesize in 15 steps the venturicidene C‐15/C‐27 segment 23, containing 8 stereogenic centers with the proper absolute configuration.
Synthesis of HR 916 B: The First Technically Feasible Route to the 1‐(Pivaloyloxy)ethyl Esters of Cephalosporins
Authors: Fleischmann Klaus , Adam Friedhelm , Dürckheimer Walter , Hertzsch Winfried , Hörlein Rolf , Jendralla Heiner , Wollmann Theo , Lefebvre Christian , Mackiewicz Philippe , Roul Jean‐Michel
Published: July 2007

An efficient synthesis of HR 916 B (4), the orally active 1‐(RS)‐(pivaloyloxy)ethyl prodrug ester of the cephalosporin cefdaloxime, was developed and applied on a multi‐kg scale. AMCA (8) was prepared by exchange of the acetoxy group of fermentation product ACA (7) with the nucleophile methanol under acidic conditions. Its 7‐amino group was acylated with mixed anhydride 14 to give 15. Carboxylic acid 15 was esterified with iodohydrin ester 27 or bromohydrin ester 30, respectively, to provide the acylal 16. Simultaneous removal of both the amino‐ and the oximo‐protecting group furnished the prodrug HR 916 3, which was purified and stabilized by precipitation of its tosylate salt 4. The overall yield of 4 (ratio 5/6 = 0.65) was 39% relative to AMCA (8) (four steps), 15% relative to ACA (7) (five steps).
A Formal [4 + 2] Dimerization of 9‐Cyclopropylidene‐9H‐fluorene
Authors: Dyker Gerald , Hillebrand Gerhard , Ernst Ludger , Dix Ina , Jones Peter G.
Published: July 2007

The methylenecyclopropanes 7 and 8, with aryl substituents fixed in a coplanar conformation, show an extraordinary readiness to dimerize with formation of 10 and 11, respectively.
Diels‐Alder Reactions of Tetradehydrodianthracene with Electron‐Rich Dienes
Authors: Kammermeier Stefan , Neumann Helfried , Hampel Frank , Herges Rainer
Published: July 2007

Tetradehydrodianthracene (TDDA; 1) reacts with electronrich dienes such as butadiene, cyclopentadiene and o‐quinodimethane under ambient conditions. Only 1:1 products 5–8 were observed even with a large excess of the diene and under drastic conditions (though two strained and highly pyramidalized double bonds are available). The enhanced reactivity of TDDA compared with its mono Diels‐Alder adducts is mainly due to the through‐bond and through‐space interaction of the two olefinic double bonds. During the cycloaddition one of the olefinic bonds in TDDA is converted into an extremely long C–C single bond (> 1.65 Å). Attempts to cleave the strained π‐bond thermochemically to form a diradical 13 afforded product 14a that was formed via a formal intramolecular homo 1,3‐sigmatropic shift.
Synthesis of Functionalized Cyclopentanes, Cyclohexanes and Cycloheptanes by a Silicon‐Induced Domino Reaction
Authors: Michel Tycho , Kirschning Andreas , Beier Christian , Bräuer Nico , Schaumann Ernst , Adiwidjaja Gunadi
Published: July 2007

1,3‐Functionalized cyclopentanes, ‐hexanes and ‐heptanes are obtained by addition of lithiated silyldithioacetals 7 to epoxyhomoallyl tosylates 4–6, The reaction involves a cascade of epoxide ring opening, of Brook 1,4‐rearrangement and tosylate substitution. The method is particularly suitable for the preparation of cyclopentanes, whereas cyclohexanes and ‐heptanes are formed in yields only up to 49%. Use of enantiomerically pure epoxides provides optically active cyclopentanes (S)‐10b, d, 11a as well as oxetanes (S)‐14a, b. Hydrolysis of the dithioacetal function leads to the corresponding ketones 12, Cyclization of epoxide 24b gives an anellated cyclopentane 26, the configuration of which was established by X‐ray structural analysis of dinitrobenzoate 27. Use of epoxide 29b provides the anellated tetrahydrofuran 30.
Secondary Mould Metabolites, LII. Structure Elucidation of Diatretol – A New Diketopiperazine Metabolite from the Fungus Clitocybe diatreta
Authors: Arnone Alberto , Nasini Gianluca , Pava Orso Vajna De , Capelli Silvia , Meille Stefano Valdo
Published: July 2007

In the culture broth of the fungus Clitocybe diatreta a novel diketopiperazine metabolite, diatretol (1), was detected by chemical screening. The structure was established on the basis of 1H‐ and 13C‐NMR data and single‐crystal X‐ray analysis. Diatretol exhibits a low antibacterial activity and inhibits the growth germination of Lepidium sativum.
A Convenient Synthesis of (E)‐Non‐3‐ene‐2,5‐dione, an Important Component Isolated from the Fire Bee Trigona tataira
Authors: Ballini Roberto , Astolfi Paola
Published: July 2007

(E)‐Non‐3‐ene‐2,5‐dione (5) the main component isolated from the volatile compounds derived from the cephalic secretion of workers of Trigona tataira, was conveniently prepared by nitroaldol reaction between pentanal 1 and 1‐nitrobutan‐3‐ol (rac‐2) catalyzed by Amberlyst A‐21. The resulting β‐nitro alcohol rac‐3 was oxidized to the α‐nitro ketones 4, which via elimination of nitrous acid (Et3N), afforded the enedione 5 in good yield.
Wechselwirkungen in Kristallen, 94. Donator/Akzeptor‐Komplexe von Hydrochinon, Pyren, Perylen und N, N,N′,N′‐Tetramethylbenzidin mit 1,2,4,5‐Tetracyanbenzol oder Tetracyanhydrochinon: Strukturen mit und ohne H‐Brücken‐Netzwerken
Authors: Bock Hans , Seitz Wolfgang , Sievert M. , Kleine M. , Bats Jan W.
Published: July 2007

Interaction in Crystals, 94. – Donor/Acceptor complexes between Hydroquinone, Pyrene, Perylene, and N, N,N′,N′‐Tetramethylbenzidine with 1,2,4,5‐Tetracyanobenzene or Tetracyanohydroquinone: Structures with and without H Bridge Networks

Donor/acceptor complexes {D ⃛A}∞ can be designed to crystallize in mixed stacks. Due to interplanar ring distances of double π van der Waals radii (340 pm), however, no significant structure changes are observed relative to those of their components. Therefore, it has been attempted to planarize the herringbone patterns of the crystal lattice by additional H bridge networks in order to increase the π interactions between the donor and acceptor rings. The following structural effects are observed: (i) Relative to the complex {perylene ⃛1,2,4,5‐tetracyanobenzene}∞, the planarization of the herringbone pattern by the H bridge network in {pyrene ⃛2,3,5,6‐tetracyanohydroquinone}∞ and {perylene ⃛tetracyanohydroquinone(OH2)2}∞ shortens the layer distance from 345 to 340 pm. Nevertheless, still no significant structural changes due to π electron polarization become apparent. (ii) Despite of identical crystallization conditions from acetic acid solution for both pyrene and perylene inclusion compounds, only the more spacious perylene stretches the H bridges of tetracyanohydroquinone (OH ⃛NC)2 by hydrate water inclusion (OH ⃛OH2 ⃛NC)2 from 265 to 555 pm. (iii) In the complex {hydroquinone ⃛1,2,4,5‐tetracyanobenzene}∞ the phenolic OH substituents generate an extensive H bridge network within the mixed‐staple layers, in which each hydroquinone is surrounded by four tetracyanobenzenes via both strong (OH ⃛NC) and weak (CH ⃛OH) contacts. (iv) In the complex {(tetracyanohydroquinone−)2 ⃛(N, N,N′,N′‐tetramethylbenzidinium(H2+)(OH2)2} an additional proton transfer turns the hydroquinone anion into the donor and the doubly protonated benzidinium dication into the acceptor. – Additional UV/Vis spectroscopic investigations prove long‐wavelength charge transfer bands between 11200 and 19000 cm−1, which are shifted relative to the component absorptions by partly up to 1.5 eV (!) and can be approximated by AM1/CI or PM3/CI calculations. The missing structural changes in the ground state of the complexes {D ⃛A∞} demonstrate therefore, that the electron transfer from donor to acceptor is largely initiated on excitation.
Photochemical Activation of Amino Acids: From the Synthesis of Enantiomerically Pure β,γ‐Unsaturated Amino Acids to Macrocyclic Ring Systems
Authors: Griesbeck Axel G.
Published: July 2007

Amino acids whose amino groups are transformed into phthalimido chromophores are versatile substrates for photochemical transformations such as cyclization, isomerization, and β‐cleavage. These processes are initiated by homolytic or mesolytic CH activation and depend on the spin state of the excited substrate. Derivatives of α‐amino acids without strong electron‐donating substituents [Abu, Nva, Val, Leu, Ile, Tle, Phe, Met(SO)] react by initial homolytic CH activation and solely via their first excited singlet states, whereas substrates with strong electron‐donating substituents (Tyr, DOPA, Met, Glu, Asp) react by initial photoinduced electron transfer (PET) followed by mesolytic CH activation and solely via their first excited triplet states. The S‐alkyl cysteine derivatives are the only ones which show competing singlet and triplet state reactivity with pronounced spin‐determined regioselective CH activation. The amino dicarboxylic acids Glu and Asp could be applied as the carboxylates in PET reactions, a strategy which also opened up a new synthetic approach to medium‐ and large‐ring systems.
Cyclopropyl Building Blocks for Organic Synthesis, 37. Synthesis and Diels—Alder Reactions of 2‐Substituted 2‐Cyclopropylideneacetates in Comparison with Allenecarboxylate and Ordinary Acrylates
Authors: de Meijere Armin , Teichmann Stephan , Seyed‐Mahdavi Fereydoun , Kohlstruk Stephan
Published: July 2007

Several new 2‐substituted 2‐cyclopropylideneacetates 1a‐X (X=F, N3, SPh, OTBDMS, OTBDPS) have been prepared. Their cycloadditions and those of some previously described compounds of type 1a‐X (X=H, Br, Cl) with furan (5) and/or 6,6‐dimethylfulvene (7) are reported. Several of these peculiar acrylates 1a‐X (X=H, Br, Cl, F, N3), as well as allenecarboxylate 1b, regular acrylate 1c, crotonate 1d, and 3,3‐disubstituted acrylates 1e‐X (X=H, Cl), were reacted with furan (5) and 6,6‐dimethylfulvene (7) in two series of competition experiments at 64°C. The [2 + 4] cycloaddition of 1a‐Cl and 1a‐Br to furan (5) are both about 16 times as fast and to dimethylfulvene (7) 230 and 210 times as fast as that of the parent acrylate 1c, while allenecarboxylate 1b reacts with 4 only 30 times as fast as 1c, and the 3‐substituted acrylates 1d and 1a‐X (X=H, Cl) were all too sluggish to react under these conditions. The kinetic data obtained for the cycloadditions of 1a‐X suggest a mechanism involving either diradicals or zwitterions as intermediates.
Coupling of Alkynyl(2,4,6‐tri‐tert‐butylphenyl)phosphanes with Cuprous Chloride
Authors: Märkl Gottfried , Hennig Rüdiger
Published: July 2007

Coupling of alkynyl(2,4,6‐tri‐tert‐butylphenyl)phosphanes 2 with n‐butyllithium and cuprous chloride gives 3,4‐diphospha‐1,5‐hexadiynes 3 or cuprous chloride complexes 8 of 3,4‐bis(phosphinidene)cyclobutenes 5, depending on the bulkiness of the substituent at the triple bond. The exclusive formation of racemic 3,4‐diphospha‐1,5‐hexadiynes 3, which was proven by 31P‐ and 13C‐NMR spectroscopy, explains the stereoselective rearrangement to only symmetrical cyclobutenes 5.
Electron‐Transfer Chemistry and Redox‐Switching of Stilbene‐Like Heteroaromatic Compounds — Syntheses, Optoelectrochemical and ESR/ENDOR Studies
Authors: Spreitzer Hubert , Scholz Markus , Gescheidt Georg , Daub Jörg
Published: July 2007

Redox‐active compounds, in which the electron donor and the acceptor subunits are covalently linked by a vinylene spacer group were synthesised and their properties were investigated by cyclovoltammetry, spectroelectrochemistry, and ESR/ENDOR spectroscopy. — 10‐Methylphenothiazinyl, 10‐methylphenoxazinyl, and phenoxathiinyl were used as electron‐donating groups whereas 9,10‐anthraquinon‐2‐yl and phenyl groups were employed as acceptors. The synthesis of the push‐pull‐substituted stilbenes 1a, 1b, 1c, 2a, 2b and 2c was achieved by Wittig coupling of the heterocyclic aldehydes with the anthraquinoyl or phenyl phosphonium salts. The diastereoisomers were separated either by chromatography or by crystallization. — The redox potentials of the (Z) and (E) isomers differ only slightly. Spectroelectrochemical measurements indicate that the radical cations of the phenothiazine and phenoxazine derivatives undergo rearrangement from the (Z) to the (E) isomers. On the other hand, electron attachment leads to configurationally stable radical anions. This behaviour is rationalised in terms of the electron distribution reflected by the hyperfine data established by ESR/ENDOR spectroscopy.
A Facile Stereoselective Synthesis of Sphingosine and Ceramide
Authors: Li Yun‐Long , Wu Yu‐Lin
Published: July 2007

Flexible syntheses of sphingosine and ceramide were achieved by using D‐xylose as the chiral pool and a CuCN‐catalyzed allylic alkylation reaction of a dimesylate 8 for chain elongation with concomitant control of an E configuration of the double bond.
Secondary Metabolites by Chemical Screening, 34. – Aspinolides and Aspinonene/Aspyrone Co‐Metabolites, New Pentaketides Produced by Aspergillus ochraceus
Authors: Fuchser Jens , Zeeck Axel
Published: July 2007

New 10‐membered lactones, named aspinolide A–C (3, 4, 5), and the aspinonene/aspyrone co‐metabolites, named trienediol (6), isoaspinonene (7), dihydroaspyrone (8), and dienetriol 9 were discovered by chemical screening methods in the cultures of Aspergillus ochraceus (DSM‐7428) under altered fermentation conditions. The structures were established by detailed spectroscopic analysis. The polyketide origin of the skeleton and the biogenesis of the oxygen atoms were verified by feeding sodium [1,2‐13C2]acetate and [18O2] gas, respectively, to growing cultures of the fungus. A comprehensive discussion of the supposed biosynthetic pathways draws the conclusion that two polyketide synthases (PKSα, PKSβ) exist, forming two different series of pentaketides in parallel. One pathway leads to branched‐chain metabolites by a Favorski‐like rearrangement of an epoxide intermediate, while the other involves detachment of the pentaketides from the PKSβ by lactonisation without any rearrangement of the carbon skeleton. The former pathway is affected by an inhibitor of cytochrome P450 dependent monooxygenases.
Synthesis of S‐α‐D‐Glucosylated L‐Cysteine – A Novel S‐Glycosyl Amino Acid
Authors: Käsbeck Ludwig , Kessler Horst
Published: July 2007

Whereas S‐β‐D‐glucosylated L‐cysteine is easily available, the corresponding α‐anomer has not been prepared before. In this paper a solution to the synthetic problem is presented. The glycosylation of highly nucleophilic N‐phthaloyl‐L‐cysteine esters 4 and 5 with 2,3,4,6‐tetra‐O‐benzyl‐α‐L‐glucopyranosyl trichloroacetimidate in the presence of 1 equivalent of BF3 · Et2O provided the protected cysteinyl‐S‐α‐glycosides 6 and 7 in good yields. These S‐α‐glycosylated cysteine derivatives were only available by use of the non‐urethane N‐protected glycosyl acceptors 4 and 5. Palladium‐catalyzed hydrogenolysis and subsequent hydrazinolysis of the benzylated compound 7 afforded L‐cysteinyl‐S‐α‐D‐glucoside 1, a novel S‐glycosyl amino acid.
1,3‐Dipolar Cycloadditions, 97. – Some Cycloadditions of Aromatic Thione S‐Oxides
Authors: Huisgen Rolf , Mloston Grzegorz , Polborn Kurt , Palacios‐Gambra Francisco
Published: July 2007

Surprisingly, thiobenzophenone S‐oxide (5) and thione 6 afforded the spiro‐1,2,4‐trithiolane 7 (86%) instead of the expected spiro‐1,2,4‐oxadithiolane 16. Structure 7 was established via spectra, single‐crystal X‐ray analysis, and an independent synthesis from thiobenzophenone S‐sulfide (15) and 6. On accepting the formation of 16 by 1,3‐cycloaddition as a first step, we reduced the mechanistic problem to the conversion 16 + 6 → 15 + dione 8; three conceivable pathways are discussed. Thiofluorenone S‐oxide (25) combines with 6 to the trithiolane 27 in low yield; the spontaneous conversion of 25 to 9,9′‐bifluorenylidene (26) takes precedence. No 1,3‐cycloaddition is involved in the 1:1 reaction of 5 with (E)‐cyclooctene (28); 5 combines as a hetero‐1,3‐diene with 28 to a Diels‐Alder type adduct 30.
Application of the Chelate‐Enolate Claisen Rearrangement to The Synthesis of γ,δ‐Unsaturated Amino Acids
Authors: Kazmaier Uli
Published: July 2007

Deprotonation of N‐protected amino acid allylic esters with LDA at −78°C and subsequent addition of a metal salt presumably results in the formation of a chelated metal enolate that undergoes Claisen rearrangement upon warming up to room temperature, giving rise to γ,δ‐unsaturated amino acids. Many different metal salts can be used for chelation, but in general the best results are obtained with zinc chloride. Due to the fixed enolate geometry, as a result of chelate formation, and a strong preference for the chair‐like transition state, the rearrangement proceeds with a high degree of diastereoselectivity. This method can be applied to acyclic as well as to cyclic substrates, and even to peptides, and allows the synthesis of amino acids containing quaternary carbon centers. Esters of chiral allylic alcohols produce optically active amino acids via chirality transfer from the ester moiety to the α‐carbon center of the amino acid. Another possibility to introduce chirality is given by the rearrangement in the presence of chiral ligands. The best results are obtained if Al(OiPr)3 is used as the chelating metal salt and the Chinchona alkaloids as bidentate ligands. Quinine gives rise to (2R)‐configured amino acids, whereas quinidine delivers the (2S) derivatives in very high yields and excellent enantioselectivities (80–93% ee). The ligands can easily be recovered nearly quantitatively from the reaction mixture.
Pigments of Fungi, 68. – Phlebiachrysoic Acids, New Inhibitors of Leukotriene Biosynthesis from Phlebia chrysocrea (Basidiomycetes)
Authors: Marumoto Ryuji , Klostermeyer Dörte , Steglich Wolfgang , Wunder Annette , Anke Timm
Published: July 2007

Five yellow 2‐hydroxy‐5‐methoxybenzoquinones with C15 and C17 alkyl side chains were isolated from fruitbodies of the wood‐rotting fungus Phlebia chryoscrea. The compounds, named phlebiachrysoic acids A–E are strong inhibitors of leukotriene biosynthesis and are responsible for the red colour reaction when the fruitbodies are touched with aqueous alkali.
Bromine Complexes of Ethylene and Cyclopropene: Matrix‐IR‐Spectroscopic Identification, Photochemical Reactions, Ab Initio Studies
Authors: Maier Günther , Senger Stefan
Published: July 2007

The matrix‐isolated ethylene–bromine complex (1) and the cyclopropene–bromine complex (8) have been chosen to examine which ab initio method (MP2 or BLYP) is more suitable to calculate the IR spectra and structures of π complexes. In addition the photochemistry of 1 and 8 has been investigated and the mechanism of the photochemically induced reactions is discussed.
Enantioselective synthesis of α‐phosphanyl ketones and 2‐phosphanyl alcohols
Authors: Enders Dieter , Berg Thorsten , Raabe Gerhard , Runsink Jan
Published: July 2007

An efficient, highly enantioselective methodology for the synthesis of α‐phosphanyl ketones 7 and 2‐phosphanyl alcohols 12 and 13, important hemilable ligands for enantioselective homogeneous catalysis and chiral building blocks in general, has been developed. The key step of this first enantio‐selective synthesis of α‐phosphanyl ketones is the diastereo‐selective phosphanylation of SAMP hydrazones 2 to produce α‐phosphanyl hydrazones, isolated as the more stable borane adducts 6. Subsequent ozonolysis afforded α‐phosphanyl ketones 7. The enantioselective synthesis of 2‐phosphanyl alcohols 12 and 13 has been accomplished by two fundamentally different procedures: the phosphanylation of unsubstituted chiral aldehyde hydrazones 9 and the alkylation of α‐diphenylphopshanyl acetaldehyde SAMP hydrazone 10. After separation of the minor diastereomer, the borane‐protected α‐phosphanyl aldehyde hydrazones 11 were converted to unprotected 2‐phosphanyl alcohols 13 by ozonolysis, reduction and removal of the borane group. The absolute configuration of the functionalized phosphanes was determined by X‐ray analysis, NOE experiments or polarimetry.
Simple Synthesis of Both Enantiomers of 3‐Methyl‐N‐(3‐Methylbutyl)pyrrolidine
Authors: Veith Hans Jürgen , Collas Markus , Zimmer Reinhold
Published: July 2007

(S)‐3‐Methyl‐N‐(3‐methylbutyl)pyrrolidine (1) and its antipode (R)‐1 have been prepared by reduction of (S)‐4,5‐dihydro‐3‐methyl‐2(3H)furanone (7) and dimethyl (R)‐2‐methylsuccinate (11), bromination thereof, and ring closure of the intermediates (S)‐9 and (R)‐9, respectively, with 3‐methylbutylamine (10). An alternative synthesis of (R)‐1 by mesylation of (R)‐8 is also described. Both enantiomers of 1 were obtained in excellent enantiomeric excesses (ee = 96%).
Synthesis of a Tetraazido‐Substituted 2‐Tetrazene from 1,5‐Cyclooctadiene and Iodine Azide
Authors: Rose Bernd , Schollmeyer Dieter , Meier Herbert
Published: July 2007

In contrast to the addition of iodine azide to cyclooctene (1) or 1,3‐cyclooctadiene (5), its reaction with 1,5‐cyclooctadiene (12) leads mainly to the surprisingly stable tetraazido‐substituted 2‐tetrazene 14 The structure of this was established by 15N‐NMR studies and an X‐ray structural analysis. Treatment of 14 with hydrochloric acid yields the diazido‐substituted 9‐azabicyclo[3.3.1]nonane 20.
Synthesis of Optically Active 2‐Siloxycyclopropanecarboxylates by Asymmetric Catalysis, IV. – Influence of Nucleophilicity of Silyl Enol Ethers on Stereoselectivities in Asymmetric Cyclopropanation Reactions
Authors: Schumacher Ralf , Reißig Hans‐Ulrich
Published: July 2007

By variation of the aryl substituents of silyl enol ethers 1a–e and 1f–k, the influence of their nucleophilicity on the stereochemical outcome of cyclopropanation reactions was studied. Using the neutral Schiff‐base catalyst 2 · Cu(OAc)2, there was only a weak effect. On the other hand, with the cationic bisoxazoline complex 3· CuOTf a remarkable increase in the enantioselectivity was observed with more strongly electron‐attracting substituents such as a trifluoromethyl or nitro group.
Probing for Steric and Electronic Effects in Diastereoselective Dioxirane Epoxidations Compared to The Oxygen Transfer by Peroxy Acids
Authors: Adam Waldemar , Paredes Rodrigo , Smerz Alexander K. , Veloza L. Angela
Published: July 2007

The spiro transition state for the oxygen transfer by dioxiranes is substantiated by the fact that no enhanced steric effects are observed when dioxiranes with alkyl groups of different size are employed, as manifested by the same (within the experimental error) diastereoselectivities in the epoxidation of 2‐menthene and 1,3‐dimethylcyclohexene for different dioxiranes. The π‐facial selectivity (anti attack) in the epoxidation of the acetate and the methyl and trimethylsilyl ether derivatives of 2‐cyclohexenol derives from steric interactions, whereas a pronounced electronic effect (electrostatic repulsion) is held responsible for the high anti selectivity of peroxides such as ascaridol and 3‐hydroperoxycyclohexene. Quite generally, dioxiranes display only slightly higher diastereoselectivities than mCPBA in sterically controlled epoxidations of cycloalkenes.
Utilization of Industrial Waste Materials, 7. – Synthesis of New, Chiral β‐sec‐Amino Alcohols – Regio‐ and Diastereoselective α‐Hydroxyalkylation of (1R,5R)‐2‐Azabicyclo[3.3.0]octane
Authors: Wilken Jörg , Martens Jürgen
Published: July 2007

New, chiral β‐sec‐amino alcohols 3a–d, 4a–e, and 5a–h have been synthesized from the enantiomerically pure amine (all‐R)‐2a. For the diastereo‐ and regioselective α‐hydroxyalkylation of the chiral (all‐R)‐N‐nitroso‐2‐azabicyclo[3.3.0]octane (all‐R)‐2d, Seebach's “one pot” method was chosen. The versatile nucleophilic intermediate reacts regio‐and stereoselectively with a variety of electrophiles to afford 3‐substituted pyrrolidine derivatives, e.g. (erythro)‐(αR,βS)‐amino alcohol frameworks with four sterically crowded stereogenic centers, and (βS)‐configured tricyclic structures with a cycloalkynol building block (see formulae 3a–d, 4a–e, and 5a–h). Alkylation products are obtained in fair yields with a high degree of stereoselectivity (diastereomeric ratios dr up to 93:7). A mechanistic interpretation of the stereochemical course of this reaction is presented. – This is a further example of the synthesis of interesting new chiral ligands from the industrial waste material (all‐R)‐2‐azabicyclo[3.3.0]octane‐3‐carboxylic acid benzyl ester (all‐R)‐1a. The catalytic ability of selected (erythro)‐ and new, related stereoisomeric amino alcohol structures were tested in the enantioselective borane reduction using the prochiral acetophenone as model substrate (enantiomeric excesses ee up to 86%).
Utilization of Industrial Waste Materials, 10. – Synthesis of New Chiral Bicyclic 3‐hydroxypiperidines – Highly Diastereoselective Ring Expansion of the Azabicyclo[3.3.0]octane System to Chiral Piperidine Derivatives
Authors: Wilken Jörg , Kossenjans Michael , Saak Wolfgang , Haase Detlev , Pohl Siegfried , Martens Jürgen
Published: July 2007

New, chiral bicyclic 3‐hydroxypiperidines (4S)‐2a–e are synthesized from the β‐amino alcohols (3R)‐1a–e. In an one‐step reaction (4S)‐2a–e are obtained by a high diastereoselective ring expansion (dr ⩾ 95:5). As well, the amino alcohol (3S)‐1a leads to the corresponding rearranged epimer bicyclic piperidine derivative (4R)‐2a (dr ⩾ 95:5). Thus, it is possible to clarify the influence of the three stereogenic centers of the parent compound regarding the diastereoselectivity of the ring expansion. After oxidation of the tert‐amino sec‐alcohol (4S)‐2a to the corresponding α‐amino ketone 4, new 3‐hydroxypiperidines (4Ξ)‐5a, b12 and (4RS)‐6 are obtained by a diastereoselective Grignard addition. Furthermore, the achiral and the chiral reduction of 4 to the β‐amino alcohols (4S)‐2a and (4R)‐2a is described. These are further examples of the utilization of industrial waste material (all‐R)‐2‐azabicyclo[3.3.0]octane‐3‐carboxylic acid (all‐R)‐3.
Recent Advances in Organic Synthesis under High Pressure
Authors: Ciobanu Mona , Matsumoto Kivoshi
Published: July 2007

The most recent successes achieved in organic synthesis by use of high‐pressure technique are reviewed.
Total Synthesis of the Toxin Oosponol and of Structural Analogues and Investigation of Their Antibiotic Activities
Authors: Kovács Tibor , Sonnenbichler Isolde , Sonnenbichler Johann
Published: July 2007

The toxic metabolite of the basidiomycete Gloeophyllum abietinum, oosponol (6b), and the structural analogues (Figure 1) were synthesised in order to investigate which partial structures of the molecules are responsible for their biological activities. Different organisms were employed to test the antibiotic activities of the analogues. From the results obtained with the synthetic analogues of oosponol (6b), it became evident that the toxicity of this fungal metabolite can be attributed to a vinylogous acid anhydride structure, which in nature is produced by dehydrogenation of the nontoxic precursor oospoglycol (7).
Pheromone Synthesis, CLXXXIII. Synthesis of (1R,2R,5S,7R)‐ and (1R,2S,5S,7R)‐2‐hydroxy‐exo‐Brevicomin, the Components of the Male‐Produced Volatiles of the Mountain Pine Beetle, dendroctonus ponderosae
Authors: Takikawa Hirosato , Shimbo Ken‐Ichiro , Mori Kenji
Published: July 2007

Both (2R)‐ and (2S)‐hydroxy derivatives of (+)‐exo‐brevicomin {5‐methyl‐6,8‐dioxabicyclo[3.2.1]octan‐2‐ol; 1 and 2} were synthesized by employing Sharpless asymmetric dihydroxylation as the key reaction.
Pheromone Synthesis, CLXXXII. Synthesis of (1R,1′R,5′R,7′R)‐ and (1S,1′R,5′R,7′R)‐ 1‐hydroxy‐exo‐Brevicomin, the Components of the Male‐Produced Volatiles of the Mountain Pine Beetle, dendroctonus ponderosae
Authors: Yokoyama Yūsuke , Mori Kenji
Published: July 2007

Both (1R)‐ and (1S)‐hydroxy derivatives of (+)‐exo‐brevicomin {(1R,1′R,5′R,7′R)‐1‐(5′‐methyl‐6′,8′‐dioxabicyclo[3.2.1]‐octyl)ethanol (1) and its (1S)‐isomer (2)} were synthesized by employing Sharpless asymmetric dihydroxylation as the key reaction.
Synthesis of the Thio‐Linked Ganglioside GM3 epitope
Authors: Eisele Thomas , Schmidt Richard R.
Published: July 2007

The synthesis of sulfur‐linked GM3 epitope 2 is based on acid‐catalyzed and base‐promoted S‐glycosylation processes. As a precursor, 2‐O‐benzoyl‐3‐thiogalactoside 10 was required, and was obtained from 4,6‐O‐benzylidene‐galactoside 3 in six high‐yielding steps. Base‐promoted S‐glycosylation of 10 with neuraminic acid functionalized β‐halogenose 11 in the presence of NaH as base and Kryptofix 21 as coactivator afforded α(2‐3)‐thio‐linked disaccharide 13, which was readily converted to α‐halogenose 20. Heptyl 1‐thioglycoside 22 was obtained from O‐galactosyl trichloroacetimidate 21 and heptylthiol via acid‐catalyzed S‐glycosylation. 22 was transformed into 2,3,6‐tri‐O‐acylgalactoside 26 which, via the 4‐O‐triflate and treatment with potassium thioacetate, followed by selective removal of the S‐acetyl group, furnished the 2,3,6‐tri‐O‐acyl‐4‐thioglucoside 28. Base‐promoted S‐glycosylation of 28 with halogenose 20 led to fully acylated target molecule 29, which was quantitatively converted into 2.
Switching Selectivity in o‐Benzoquinone Cycloadditions
Authors: Al‐Talib Mahmoud , Gerstenberger Ina , Jones Peter G. , Winterfeldt Ekkehard
Published: July 2007

Whereas m‐methoxy‐o‐benzoquinone 6, like other unsaturated ketones, operates as a dienophile in Diels–Alder cycloadditions, the corresponding methyl derivative 7a behaves as an electron‐poor 4π‐system under exactly the same conditions. With the nonsymmetric cyclopentadiene 2 (X = MeO), adduct 9a is formed with excellent chemoselectivity, face‐selectivity, and regioselectivity.
The Reaction of Hexachloroacetone with Diamines
Authors: Rezende Marcos Caroli , Marques Carlos Alberto , Dall'Oglio Evandro Luiz , Zucco Cesar
Published: July 2007

The reaction of hexachloroacetone (HCA) with various diamines led either to the corresponding diamides or to cyclic ureas, depending on the molar ratio of the reactants. In the cases of ethylenediamine, 1,2‐diaminocyclohexane and o‐phenylenediamine, the reaction with HCA also formed bisimidazole derivatives. These latter unexpected products were also formed when the diamine reacted with trichloroacetate esters or with carbon dioxide.
A Crown Ether Bearing Fulgide: The Regulation of Photochromism by Supramolecular Effects
Authors: Guo Zhixin , Wang Guijun , Tang Yingwu , Song Xinqi
Published: July 2007

A novel benzo‐15‐crown‐5 modified fulgide (CF) has been prepared. The absorption spectra of CF and its colored form (CFDHN) are hypsochromically shifted and the decolouring rate of CFDHN is apparently decreased through selective cation binding.
Strategy for the Synthesis of Epoxide‐ and Carbonate‐Containing Dienediyne Models of the Neocarzinostatin Chromophore – Application to the 6‐Ring/11‐Ring Case[1]
Authors: Eckhardt Matthias , Brückner Reinhard
Published: July 2007

A novel synthetic strategy leading to bicyclic dienediyne models of the chromophore 1 of the anti‐tumor antibiotic neocarzinostatin is described. Its key step is a ring‐closing McMurry reaction of the dienediyne keto aldehydes 17 or 23. It leads to dienediynediols (compounds 19 and 24, respectively) or to trienediynes (compounds 18 and 25, respectively). Low temperatures favor the formation of dienediynediols while high temperatures favor the formation of trienediynes, so that the McMurry reactions of keto aldehyde 23 show an almost perfect temperature‐dependent chemoselectivity (Scheme 6). The trienediyne 25 contains a ketal group which was removed by acid‐catalyzed methanolysis (Scheme 8). The resulting diol 31 was mono‐tert‐butylsilylated to provide the allyl alcohol 36 (Scheme 10). It was epoxidized regio‐ and stereoselectively with Sharpless' asymmetric epoxidation reagent. The resulting epoxide 37 was converted into the dienediyne epoxycarbonate syn‐33 in the final step of a sequence totaling seven steps and 5% yield starting from the bistriflate 3b; 3b itself is accessible from 2‐formylcyclohexa none in two steps and 47% overall yield. The dienediyne epoxycarbonate syn‐33 is the first synthetic congener of the neocarzinostatin chromophore furnished both with the – correctly configured – epoxide and carbonate rings.
Chemistry of Ginkgolides, VII. Preparation and Crystal Structure Analysis of a Secondary Ozonide from Ginkgolide A
Authors: Weinges Klaus , Schick Hartmut , Pritzkow Hans
Published: July 2007

By hydrogenation of 3,14‐didehydro‐10‐hydroxyginkgolide (3,14‐anhydroginkgolide A, 1) the 3,14‐didehydro‐10‐hydroxyginkgolide‐15‐acid (2) was obtained. Reaction with diazomethane led to the methyl ester 2a, which was transformed into its MOM derivative 2b. Ozonolysis of 2b gave a stable secondary ozonide 3 and 10‐methoxymethoxy‐3‐oxo‐14,15,16‐trinorginkgolide (4).
Anellation Reactions of Pyranose Derivatives
Authors: Peseke Klaus , Thiele Gabriela , Michalik Manfred , Powell Douglas R.
Published: July 2007

The “push‐pull”‐activated pyranosidulose 1 reacts with acetylacetone and ethyl acetoacetate to give the methyl pyrano‐[2′,3′:7,8]pyrano[3,2‐D][1,3]dioxin‐9‐yl ketone 2a and the pyrano[2′,3′:7,8]pyrano[3,2‐D][1,3]dioxine‐9‐carboxylate 2b. Treatment of 1 with 1,3‐cyclohexanediones leads to the 1,3‐dioxino[5′,4′:3,4]pyrano[3,4‐B]chromen‐11‐ones 4a and 4b. Dialkyl benzo[7,8]pyrano[3,2‐D][1,3]dioxine‐7,9‐dicarboxylates 5a and 5b were obtained by reaction of ulose 1 with dialkyl 3‐oxoglutarates.
Photoaddition of 2‐Morpholinoacrylonitrile to Substituted 1‐Acetonaphthones
Authors: Memarian Hamid Reza , Nasr‐Esfahani Masoud , Boese Roland , Döpp Dietrich
Published: July 2007

Substituted 1‐acetonaphthones 6b–d and 2‐morpholinoacrylonitrile (2a) undergo a photocycloaddition. The type of addition ([2 + 2] vs. [4 + 2]) is dependent on the location of additional substituents. Whereas compound 6c with a methoxy group at C‐2 gave only the [4 + 2]‐cycloadduct 11, the formation of [2 + 2]‐cycloadducts was observed with 6b, d with cyano and methoxy groups, respectively, at C‐4. In the case of the 4‐bromo derivative 6a, photosubstitution was observed. The endo or exo orientation of the morpholino group in the cycloadducts was determined by an X‐ray crystal structure analysis for 9b, as well as by NOE signal intensity difference determination experiments for 9a and 11.
Pheromone Synthesis, CLXXXV Synthesis of the Analogues of Lurlenic Acid with a Modified Sugar Part: Chlamydomonas responds only to the D‐xyloside
Authors: Takanashi Shin‐Ichi , Mori Kenji
Published: July 2007

Six analogues of lurlenic acid [(4E,8E,12E)‐14‐[2′‐hydroxy‐3′,4′‐dimethyl‐5′‐(1″‐β‐D‐xylopyranosyloxy)phenyl]‐4,8,12‐trimethyltetradeca‐4,8,12‐trienoic acid(1)], the mating pheromone of Chlamydomonas allensworthii, were synthesized as E/Z mixtures (E/Z = 3:2) at C‐12. They possess a tetrahydropyranyl (1a), β‐L‐xylopyranosyl (1b), β‐D‐glucopyranosyl (1e) or β‐D‐arabinopyranosyl (1f) group, respectively, as the sugar part. Only lurlenic acid (1) was bioactive as the pheromone.
Synthesis of Medium and Large Rings, XLIV. Synthesis of Optically Active Bridged Bicyclobutane Derivatives
Authors: Tochtermann Werner , Panitzsch Torsten , Peschanel Matthias , Wolff Christian , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg
Published: July 2007

Irradiation of the dihydrooxepine monoester (+)‐4 gives the bridged bicyclobutane (+)‐5 in 77% yield. On the other hand, the corresponding diester 1 yields the cyclobutene 2. Possible explanations for this differing behaviour are discussed.