bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the chemistry of α‐formyl‐2‐hydroxyacetophenone
Authors: Széll T. , Sohár P. , Horváth Gy. 
Published: July 2007

AbstractThe title compound 1 undergoes cyclization and self‐condensation in the presence of dil. NaOH yielding chromone (2) and/or 1‐(3‐chromonyl)‐2‐(2‐hydroxybenzoyl)ethene (3). With benzaldehyde in the presence of piperidine in boiling ethanol, 1 reacts both by cyclization, and self‐condensation combined with cyclization to give 2, 3 and bis(3‐chromonyl‐phenyl)methane (5). If less than 0.1 M aq. NaOH is used 1 and benzaldehyde produces 3‐(α‐hydroxybenzoyl)chromone (4) which can also be converted into 5.
Synthesis of 1‐azabicyclo[3.3.1]nonadienes by intramolecular cyclization of 1‐(3‐oxo‐2‐phenylbutyl)tetrahydropyridines
Authors: Sólyom Sándor , Pallagi István , Ábrahám Gizella , Ling István , Szöllõsy Márta , Sziráki István , Jerkovich Gyula 
Published: July 2007

AbstractIntramolecular cyclization reactions were performed with 1‐(3‐oxo‐2‐phenylbutyl)‐1,2,5,6‐tetrahydropyridine derivatives 6a‐h in sulfuric acid to give 3,6‐diphenyl‐substituted 1‐aza‐bicyclo[3.3.1]nonadienes 9. The intermediate carbinols 7a‐f and 8b, c could be isolated. Carrying out the reaction in methanesulfonic acid stereoselectivity was found in the formation of carbinols with preferential production of derivatives 7. Some of the compounds 9 show remarkable dopamine uptake inhibition.
Studies on ketoses, 11. Pyranoid exo‐ and endo‐glycals from D‐fructose and L‐sorbose: Practical routes for their acquisition and some ensuing reactions
Authors: Lichtenthaler Frieder W. , Hahn Susanne , Flath Franz‐Josef 
Published: July 2007

AbstractThe reductive elimination of the benzoylated β‐D‐fructopyranosyl and α‐L‐sorbopyranosyl bromides 10 and 23 has been examined in order to determine suitable conditions for effecting the elimination from the exo‐ as well as the endo‐positions. Exposure of 10 and 23 to Zn/HOAc or Zn/N‐methylimidazole gave the tribenzoates of exo‐D‐fructal (1) and exo‐L‐sorbal (25), in yields of 79 and 80%, respectively; minor products (ca, 10% each) were the corresponding endo‐D‐fructal (6) and endo‐L‐sorbal esters (26). For the reductive elimination to occur primarily from the endo‐position, enhancement of the leaving group capacity of the respective ring acyloxy group was required, and materialized via the 3‐O‐mesyl analogues of fructosyl bromide 10, which smoothly reacted with Zn/HOAc to give the endo‐D‐fructal esters 20 and 21; their yields, over the five steps from diacetone‐fructose, were in the 50% range. Accordingly, the methodology for generating ketose‐derived glycal esters in exo‐ or endo‐version, is now available. Some ensuing reactions of the exo‐glycals have been exploited, that is, their ozonolysis to the respective pyranoid pentonolactones, and their hydrogenation to 1,5‐anhydro‐6‐deoxy‐hexitols.
Pheromone synthesis, CLXXI. A new synthesis of (2E,4E,6R10R)‐4,6,10,12‐tetramethyl‐2,4‐tridecadien‐7‐one (matsuone), the primary component of the sex pheromone of three Matsucoccus pine bast scales
Authors: Mori Kenji , Furuuchi Takeshi , Matsuyama Keisuke 
Published: July 2007

AbstractA new synthesis of (2E,4E,6R,10R)‐4,6,10,12‐tetramethyl‐2,4‐tridecadien‐7‐one (1; matsuone) was achieved by starting from (2R,3S)‐4‐(tert‐butyldiphenylsilyloxy)‐2,3‐epoxy‐1‐butanol (21 = E) and methyl (R)‐3‐hydroxy‐2‐methylpropanoate (2 = I). Cleavage of 21 with trimethylaluminium afforded 22 as the major product (56%) and a mixture (14%) of 23 and 24. The abnormal minor product 24 was generated by the migration of a phenyl group from the silicon to a carbon atom.
Synthesis of carbon‐bridged N‐acetyl‐c‐lactosamine and derivatives
Authors: Eisele Thomas , Ishida Hideharu , Hummel Gerd , Schmidt Richard R. 
Published: July 2007

Abstract4‐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

AbstractSulfenes 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 HeterocyclesThe 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

AbstractThe 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

AbstractModel 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

AbstractThe 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

AbstractMethanesulphonyl 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

Abstractα,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

AbstractAb 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

AbstractThe 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

AbstractOxidation 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

AbstractThree 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‐DidehydronaphthaleneThe 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

AbstractChain 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

AbstractAn 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

AbstractThe 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

AbstractTetradehydrodianthracene (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

Abstract1,3‐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

AbstractIn 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

Abstract(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.