bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal and Photochemical Reactions of 1,2‐Annelated Barrelenes and Hydrobarrelenes in the presence of transition‐metal carbonyls
Authors: Trifonov Latchezar S. , Orahovats Alexander S. 
Published: December 2004

AbstractThe [Co2(CO)8]‐mediated retro‐Diels‐Alder reaction of the annelated barrelenes 1 afforded the 1H‐indol‐2(3H)‐one derivatives 3 (Scheme 1), while the hydrobarrelene 4a, under the same conditions, was converted to the anilide 6 (Scheme 2); 4b remained unaffected. The direct irradiation of 1 led to the annelated cyclooctatetraenes 7 (Scheme 3). On irradiation in the presence of excess of [Fe(CO)5], 1a, 1b, and 4a gave the tricarbonyliron complexes 8, 9, and 11, respectively (Schemes 3 and 4); under these conditions, 4b was inert.
Synthesis of (+)‐(4S, 8R)hyphen;8hyphen;Epi‐ and (−)‐(4R, 8S)‐4‐Epi‐β‐bisabolol
Authors: Fráter Georg , Müller Urs 
Published: December 2004

AbstractThe first total enantioselective synthesis of (+)‐(4S, 8R)‐8‐epi‐β‐bisabolol(+)‐1 and of (−)‐(4R, 8S)‐4‐epi‐β‐bisabolol ((−))−1) is reported. The key step in the synthesis is the kinetic resolution of (±)−5 by means of the Sharpless epoxidation yielding (−)‐ and (+}−6, respectively. Reduction of the epoxides with LiAlH4 gave the diols (+)‐and(−)−7 which were transformed into (+)‐ and (−)−8, respectively, via the corresponding mesylate. Reaction of these epoxides with the Grignard reagent derived from homoprenylbromide, assisted by Li2CuCl4, finished the synthesis of the target compounds 1 with high diastereo‐ and enantioselectivity.
Studies on the Biosynthesis of Spirostaphylotrichin A
Authors: Sandmeier Peter , Tamm Christoph 
Published: December 2004

AbstractIncorporation of 14C‐labelled acetate and amino acids as well as of [1‐13C]‐, [2‐13C]‐, and [1,2‐13C2] acetate, L‐[methyl13C] methionine, [2,3‐13C2] succinate, and L‐[2,3‐13C2] aspartate into spirostaphylotrichin A (1) by Staphylotrichum coccosporum demonstrates that the building blocks of 1 are 5 units of acetate/malonate, 1 unit of methionine, and a C4‐dicarboxylic acid. The latter is most likely aspartate and derived from the citric‐acid cycle. Using [2‐13C, 2‐2H3] acetate as a precursor, the starter unit of the polyketide chain was identified.
Struktur/wirkung‐Beziehungen bei Geruchsstoffen mit dem Bicyclo[2.2.2.]octan‐Gerüst
Authors: Spreitzer Helmut , Buchbauer Gerhard , Reisinger Sigrid 
Published: December 2004

Structure‐Activity Relationships of Odorants with a Bicyclo[2.2.2]octane SystemThe synthesis of the olfactory interesting homonojigikualcohol 2 and of its epimer 10 leads to the keto alcohols 6a, b and 7a, b as intermediates. The latter have OH and CO groups (an AH/B system) fixed at the rigid bicyclic nucleus at different distances (2.8 and 4.7 Å) and confirm Ohloff's rule for odoriferous properties which is based on this distance.
Structure‐Activity Relationship in Ambergris‐Type Woody Odorants possessing a hydronaphthalene skeleton
Authors: Vial Christian , Thommen Walter , Näf Ferdinand 
Published: December 2004

AbstractA series of methyl hydronaphthyl alcohols, formates, acetates, and ketones were prepared and their odour properties evaluated. Minor structural changes, even opposite to the osmophoric group, were found to have major effects on the odour. 13CNMR shift assignments of the hydronaphthyl derivatives are presented.
Complex formation equilibria of L‐Amino‐Acid amides with copper(II) in aqueous solution
Authors: Dallavalle Francesco , Fisicaro Emilia , Corradini Roberto , Marchelli Rosangela 
Published: December 2004

AbstractProtonation and Cu(II) complexation equilibria of L‐phenyhilaninamide, N2‐methyl‐L‐phenylalaninamide, N2, N2‐dimethyl‐L‐phenylalaninamide, L‐valinamide, and L‐prolinamide have been studied by potentiometry in aqueous solution. The formation constants of the species observed, CuL2+, CuL, CuLH, CuL2H and CuL2H−2, are discussed in relation to the structures of the ligands. Possible structures of bisamidato complexes are proposed on the ground of VIS and CD spectra. Since Cu(II) complexes of the present ligands (pH range 6–8) perform chiral resolution of dansyl‐ and unmodified amino acids in HPLC (reversed phase), it is relevant for the investigation of the resolution mechanism to know which are the species potentially involved in the recognition process.
Synthesis of ethyl cis 2‐[(Diethoxyphosphoryl)methyl]‐7‐oxo‐3‐phenyl‐6‐phthalimido‐l‐azabicyclo[3.2.0]hept‐3‐ene‐2‐carboxylate and Methyl cis‐2‐Bromo‐3‐methyl‐8‐oxo‐7‐phthalimido‐4‐oxa‐1‐azabicyclo[4.2.0]octane‐2‐carboxylate
Authors: Hakimelahi Gholam H. , Jarrahpour Ali A. 
Published: December 2004

AbstractThe synthesis of a Δ1‐carbapenem and two β‐lactams possessing a Br‐atom at the N‐substituting center not involved in the lactam ring and bearing the carboxyl group is described. The β‐lactams having this kind of Br‐substitution are more susceptible to nucleophilic attack than those having a conjugated double bond with the N‐atom of the β‐lactam ring. DBU is found to be an excellent reagent for the elimination of the silyloxy function. Moreover, a simple method for the addition of diethyl phosphite to an α, β‐unsaturated double bond using a catalytic amount of NaH is described.
Synthese von (+)‐Aspicilin mit Bausteinen aus nachwachsenden Rohstoffen
Authors: Quinkert Gerhard , Fernholz Erhard , Eckes Peter , Neumann Doris , Dürner Gerd 
Published: December 2004

Synthesis of (+)‐Aspicilin Using Building Blocks from Renewable ResourcesThe 18‐membered lichen macrolide (+)‐aspicilin (1) is easily built up from compounds 14, 16, 3, and 24 following the C3 + C7 + C6 + C2 = C18 pattern (see Schemes). The synthesis requires 15 steps and gives 1 in 13% overall yield from D‐mannose (2). The latter compound provides the stereogenic centers C(4), C(5), and C(6). The stereogenic center C(17) is supplied by building block 14 (from (−)‐(S)‐ethyl lactate).
Synthesis, Reactivity, and Application as Chiral Auxiliaries of the novel (3R)‐ and (3S)‐4,5‐dihydro‐3‐hydroxy‐4,4,5,5‐tetramethyl‐3‐phenylfuran‐2(3H)‐ones in the Paterno‐Büchi reaction
Authors: Oppenländer Thomas , Schönholzer Peter 
Published: December 2004

AbstractBoth enantiomers of the novel α‐hydroxy‐γ ‐lactone (±)‐3 (4,5‐dihydro‐3‐hydroxy‐4,4,5,5‐tetramethyl‐3‐phenylfuran‐2(3H)‐one) have been synthesized via hydrolysis of the oxetanes 2 derived from the photochemical [2 + 2] cycloaddition of the ketones 1 and 2,3‐dimethylbut‐2‐ene (Paterno‐Büchi reaction) involving conventional separation of diastereoisomers (Schemes 2 and 3). The absolute configuration of (R)‐ and (S)‐3 and of the corresponding oxetane precursors could be assigned on the basis of an X‐ray structural analysis of the (−)‐(1S, 4R)‐camphanoyl derivative (3′S)‐5 of (S)‐3. O‐Acylation of (S)‐and (±)‐3 to yield a variety of derivatives ((3′S)‐ and (3′RS)‐5, (S)‐ and (±)‐7, (±)‐8, (±)‐9) was accomplished by deprotonation with BuLi at room temperature and subsequent quenching of the Li alcoholate with acyl chlorides or acid anhydrides, demonstrating the extraordinary chemical stability of 3. Additionally, the course of the temperature‐dependent diastereoselective Paterno‐Büchi reaction of 2,3‐dimethylbut‐2‐ene to the benzoylformate (S)‐7 ( = (S)‐1d; obtained from (S)‐3) was shown to proceed with 58% de at 60°, leading to a decrease of enantiomeric purity in the hydrolysis product 3.
Photochemistry of ethyl 2,3‐dihydro‐2,2‐dimethyl‐3‐oxo‐1H‐pyrrole‐1‐carboxylate
Authors: Patjens Jan , Margaretha Paul 
Published: December 2004

AbstractThe title compound 7 is obtained by reductive dehalogenation from 4‐bromo‐2,3‐dihydro‐2,2. ‐dimethyl‐3‐oxo‐1H‐pyrrole‐1‐carboxylate (8) in 90% yield, Aza‐enone 7 undergoes [2 + 2] cycloaddition from the triplet state with both electron‐rich and electron‐deficient alkenes. The behaviour of 7 in light‐induced reactions is compared to those of 2,2‐dimethyl‐3(2H)‐furanone (1a) and of the corresponding thiophenone 1b. In the photodimerization and the cycloaddition to either 2,3‐dimethylbut‐2‐ene or to dimethyl maleate of these ketonic five‐membered heterocycles with one heteroatom, the overall efficiency increases in going from the furan 1a to the thiophene 1b and to the pyrrole 7.
New Cell Growth‐Inhibitory Cyclohexadienone Derivatives from Hypericum calycinum L.
Authors: Decosterd Laurent A. , Stoeckli‐Evans Helen , Chapuis Jean‐Charles , Sordat Bernard , Hostettmann Kurt 
Published: December 2004

AbstractThe crude petroleum‐ether extract of the aerial parts of Hypericum calycinum L. (Guttiferae) exhibited in vitro growth‐inhibitory activity against the Co‐115 human colon carcinoma cell line. Bioassay‐guided fractionation of this extract allowed the isolation of the cyclohexadienone derivatives 1–5, four of which are previously undescribed compounds. The structures of the known chinesin II (1) and of 2 (hypercalin A) were established by 1H‐ and 13C‐NMR spectroscopy and were confirmed by X‐ray analysis of their crystalline mixture which revealed the complete relative configuration of both compounds. The structure of 3 (hypercalin B) was elucidated by means of extensive 1D‐ and 2D‐NMR experiments, including DQ‐COSY, HETCOR and LR‐HETCOR. The structure of compound 4 (hypercalin C) was established by 1H‐ and 13C‐NMR spectroscopy and confirmed by X‐ray analysis to be the 3,5‐dihydroxy‐4‐{[(1R*,2S*, 5S*)‐2‐hydroxy‐2‐methyl‐5‐(1‐methylethenyl)cyclopentyl]methyl}‐6,6‐bis‐(3‐methylbut‐2‐enyl)‐2‐(2‐methylpropanoyl)cyclohexa‐2,4‐dien‐1‐one. The structures of the higher isomeric homologues 5a/5b were deduced by comparison of their UV, 1H‐, and 13C‐NMR spectra with those of 4. The isolated compounds appeared to be related to chinesin I and II previously isolated from Hypericum chinense L. and were responsible for the growth‐inhibitory activity of the extract against the Co‐115 human carcinoma cell line. Moreover, 1/2 and 3 showed molluscicidal activity against the schistosomiasis‐transmitting snail Biomphalaria glabrata.
Methyl‐jasmonat: Ein kurzer Weg zum Naturstoff und seinem unnatürlichen Enantiomer via Palladium(0)‐induzierte, enantiodivergente Alkylierung von Cyclopent‐2‐en‐1,3‐diol‐Derivaten
Authors: Montforts Franz‐Peter , Gesing‐Zibulak Ingrid , Grammenos Wassilios , Schneider Manfred , Laumen Kurt 
Published: December 2004

Methyl Jasmonate: A Short Synthesis of Naturally Occurring Methyl Jasmonate and its Unnatural Enantiomer via Enantiodivergent Alkylation of Cyclopent‐2‐ene‐1,3‐diol Derivatives by Palladium(0)‐Induced ReactionsPalladium‐catalyzed alkylation of cyclopent‐2‐ene‐1,2‐diol derivatives like 2 is a useful method for enantiodivergent functionalization, resulting in both enantiomeric series of chiral building blocks. The chiral building blocks 3 and 13 can be transformed to methyl jasmonate (1)and its unnatural enantiomer ent‐1, recent statement [1b] that 1 has no odour at all and that ‘methyl jasmonate's’ fragrance is actually due to its cis‐isomer ent‐11 has been confirmed also for the enantiomeric series.
Tetrazinodiheteroarene: ‘Charge‐Transfer’‐Komplexbildung mit Akzeptorverbindungen
Authors: Hellrung Bruno , Balli Heinz 
Published: December 2004

Charge‐Transfer Complexes of Tetrazinodiheteroarenes with Acceptor CompoundsThe formation of charge‐transfer complexes and radical‐ion pairs of donor compounds 1–6 with acceptor compounds 7–12 has been investigated by means of VIS/NIR‐spectroscopic methods. The equilibrium constants KCT up to 1100M‐1 for the donor/acceptor couple dipyrido[1,2‐b:1,2′‐e][1,2,4,5]tetrazine (2)/ethylenetetracarbonitrile (11) and spectra of the CT complexes have been determined in 1,2‐dichloroethane solution at 25°. Results are discussed in relation to known CT‐complex properties and to voltammetric redox‐potentials E1/2.
Preparation, Characterisation, and Structure of N‐Methylated Derivatives of 1,3,5‐Triamino‐1,3,5‐trideoxy‐cis‐inositol: Polyalcohols with Unusual Acidity
Authors: Hegetschweiler Kaspar , Erni Isidor , Schneider Walter , Schmalle Helmut 
Published: December 2004

Abstract1,3,5‐Trideoxy‐1,3,5‐tris(dimethylamino)‐cis‐inositol (TDCI) and 1,3,5‐trideoxy‐1,3,5‐tris(trimethylammonio)‐cis‐inositol (TTCI) were prepared by methylation of 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol (TACI). The ability of TDCI to form both intermolecular and intramolecular H‐bonds, as demonstrated by X‐ray diffraction, is probably responsible for the good solubility of TDCI in almost every common solvent. TTCI was found to be a polyol of unusual high acidity (pK1 = 8.14 ± 0.02, pK2 = 13.0 ± 0.2). This phenomenon could be explained by electrostatic interactions between the charged substituents of the cyclohexane residue.
Metal Complexes with Macrocyclic Ligands. Part XXXII. Reactivity studies of the pendant carboxylic group in a macrocyclic Cu2+ complex towards amide formation and its use as a protein‐labelling agent
Authors: Studer Martin , Kaden Thomas A. , Mäcke Helmut R. 
Published: December 2004

AbstractThe Cu2+ complex of 1, having a non‐coordinating carboxylic group, can be reacted under the typical conditions of peptide formation with amines such as 2‐methylpropylamine or (pyrid‐2‐yl)methylamine to give, after removal of Cu2+ with CN−, the amides 4 and 5. The Cu2+ ion is of paramount importance since it protects the four amino groups of the macrocycle so that the amide condensation can specifically be done with the exogenous amine It is also shown that the Cu2+ complex of 1 can be covalently attached to bovine serum albumin (BSA), thus opening the possibility to use this compound as a labelling agent for proteins and antibodies.
Synthesis, Reactivity Studies, and X‐ray Crystal Structure of (11R)‐25‐O‐Deacetyl‐11‐deoxo‐11‐hydroxy‐21,23‐O‐isopropylidenerifamycin S
Authors: Bartolucci Cecilia , Cellai Luciano , Cerrini Silvio , Lamba Doriano , Segre Anna Laura , Brizzi Vittorio , Brufani Mario 
Published: December 2004

AbstractThe protected intermediate (11R)‐25‐O‐deacetyl‐11‐deoxo‐11‐hydroxy‐21,23‐O‐isopropylidenerifamycin S (7) has been synthesized starting from rifamicin S (2; Scheme 2), the former being a potential substrate for the preparation of new types of rifamicin‐S derivatives modified at C(11) and/or C(25). The reactivity of 7 toward acylations has been studied under both base‐ and acid‐catalyzed conditions. The compound either did not react or nr underwent unexpected reactions, and no acylation products could be isolated. The X‐ray crystal structure of 7 reveals that both OH groups at C(11) and C(25) are hindered, and this is probably the reason, why other take place faster than acylation.
Catalysis of Ion Transfer by Tetraphenylborates in Neutral Carrier‐Based Ion‐Selective Electrodes
Authors: Gehrig Peter , Morf Werner E. , Welti Martin , Pretsch Ernö , Simon Wilhelm 
Published: December 2004

AbstractFor certain ionophores of extremely high lipophilicity, kinetic limitations of the carrier‐induced ion transfer between aqueous and membrane phase may heavily disturb the electromotive behaviour of the ion‐selective membrane electrode. These limitations may be overcome by adding tetraphenylborates to the membrane phase. Membranes prepared with different 3,6‐dioxaoctanediamide homologues and potassium tetrakis(P‐chlorophenyl)borate as phase‐transfer catalyst all exhibit the same ion selectivity as well as theoretical electrode response. This behaviour is corroborated by a theoretical description of the ion‐transfer process.
Dehydrosulfurization of Isothiocyanates by Gas‐Phase Fe(I) Cations
Authors: Eller Karsten , Akkök Semiha , Schwarz Helmut 
Published: December 2004

AbstractBare Fe(I) cations act in the gas phase as dehydrosulfurization catalysts for butyl isothiocyanate by specifically coupling the S‐atom with remote H‐atoms from the ω and (ω − l) position of the alkyl chain. Other losses induced by Fe(I) are due to ‘remote functionalization’, the formation of ion/dipole intermediates, and insertion/β‐hydrogen shift processes.
Isolation of the Cembranoid Preverecynarmin Alongside Some Briaranes, the Verecynarmins, from Both the Nudibranch Mollusc Armina maculata and the Octocoral Veretillum cynomorium of the East Pyrenean Mediterranean Sea
Authors: Guerriero Antonio , D'Ambrosio Michele , Pietra Francesco 
Published: December 2004

AbstractIt is shown that the nudibranch mollusc Armina maculata and its prey, the pennatulacean octocoral Veretillum cynomorium, of east Pyrenean waters contain a novel cembranoid, preverecynarmin ((+)‐8), besides the known cembranoid cembrene C (9) and three further briarane diterpenoids (verecynarmin E ((−)‐5), F ((−)‐6), and G ((−)‐7)). A biogenetic scheme is proposed.
Regiochemical Trends in Intramolecular [2 + 2] Photocycloadditions of 6‐(prop‐2‐enyl)cyclohex‐2‐enones and 5‐(prop‐2‐enyl)cyclopent‐2‐enones
Authors: Cruciani Giuliano , Margaretha Paul 
Published: December 2004

AbstractThe effect of substituents (X  H, Me, or F at C(6), R  H or Me at C(2′) of the allyl side chain) on the photoisomerization (λ = 350 nm) of 6‐allylcyclohex‐2‐enones 1 in MeCN is studied. Substituents X control the overall efficiency of intramolecular [2 + 2] photocycloadduct formation (Φ: Me > F > H) but do not exercise an influence on the orientation of addition of the exocyclic double bond to the enone CC bond. In contrast, replacement of the prop‐2‐enyl (R  H) by a 2‐methylprop‐2‐enyl (R  Me) side chain causes a change in the tricyclo[3.3.1.02,7]nonan‐6‐one 4 vs. tricyclo[4.2,1.03,8]nonan‐7‐one (5) product ratio from 100:0 (R  H) to roughly 2:1 (R  Me) but has almost no bearing on the relative rates of conversion of 1 to products. For C(6)‐unsubstituted enones 1aa and 1ba (X  H), the efficiency of cyclization becomes low enough so that lumiketone rearrangement to bicyclohexanones 6 and 3‐isopropylcyclopent‐2‐enones 9 becomes competitive. Enones 9 undergo consecutive intramolecular [2 + 2] photocycloaddition to tricyclo[3.2.1.03,6]octan‐2‐ones 7 and to tricyclo[3.2.1.03,6]octan‐7‐ones 8, compounds 8 only being formed when R  Me.
Halochrome Moleküle 9. Mitteilung[1]. Substituierte 6,11‐Dihydrospiro[[1]benzopyrano[4,3‐b]indol‐6,9′‐9′H‐xanthen]‐2′,6′‐diamine und ihre Aza‐analogen: Neue Chromogene für schwarze Farbbilder
Authors: Gunzenhauser Sigmund , Balli Heinz 
Published: December 2004

Halochromic Molecules. Substituted 6,11‐Dihydrospiro[[1]benzopyrano[4,3‐b]indol‐6,9′‐9′H‐xanthene]‐2′,6′‐diamines and Their Aza Analogues: New Chromogenes for Black Images.We have synthesized a series of substituted 6,11‐dihydrospiro[[1]benzopyrano[4,3‐b]indo1‐6,9′‐9′H‐xanthene]‐2′,6′‐diamines and their respective aza analogues. These compounds develop a black colour in acidic media. The assumed structures of the analytically pure starting and final products are consistant with the fragmentations in the MS and are also supported by FT 1H‐NMR. The UV/VIS spectra in buffered MeOH/H2O solutions were measured. From the ϵpH* curves, we determined the pK* values. The title compounds can be used in so‐called pressure‐sensitive copying systems.
Synthesis of the Enantiomerically Enriched Macrocyclic Lactones (+)‐(S)‐ and (−)‐(R)‐Phoracantholide I and (+)‐(S)‐Tetradecan‐13‐olide
Authors: Stanchev Stephan , Hesse Manfred 
Published: December 2004

AbstractSynthesis of two naturally occurring macrocyclic lactones is described. (−)‐(R)‐Phoracantholide I ((−)‐1; Scheme 2) was synthesized by asymmetric and chemoselective reduction of the side‐chain CO group of (−)4‐(1‐nitro‐2‐oxocyclohexyl)butan‐2‐one ((−)‐6) with (R)‐Alpine‐Hydride (47% ee). It was shown that the formation of only one diastereoisomer of the hemiacetal 5, by methylation with (i‐PrO)2TiMe2 of ketoaldehyde (−)‐2 is thermodynamically controlled. (+)‐(S)‐Tetradecan‐13‐olide ((+)‐10) was obtained by reduction of diketone (±)‐11 with optically active borohydrides followed by denitration (Scheme 3).
Dipolare (1:1)‐Addukte aus der Reaktion von 3‐Amino‐2H‐azirinen mit 1,3,4‐Oxadiazol‐ und 1,3,4‐Thiadiazol‐2(3H)‐onen
Authors: Ametamey Simon M. , Vincent Beverly R. , Heimgartner Heinz 
Published: December 2004

Dipolar 1:1 Adducts from the Reaction of 3‐Amino‐2H‐azirines with 1,3,4‐Oxadiazol‐ and 1,3,4‐Thiadiazol‐2(3H)‐ones3‐Amino‐2H‐azirines 1 react with 5‐(trifluoromethyl)‐1,3,4‐oxadiazol‐2(3H)‐one (2) as well as with different 5‐substituted 1,3,4‐thiadiazol‐2(3H)‐ones (5a–e) in 2‐propanol at room temperature to give dipolar 1:1 adducts of type 3 and 6, respectively, in reasonable‐to‐good yields (Schemes 3 and 6, Tab. 1 and 2). The structure of two of these dipolar adducts, 6a and 6e, which are formally donor‐acceptor‐stabilized azomethin imines, have been elucidated by X‐ray crystallography (Figs. 1‐4). In the reaction of 2 and sterically crowded 3‐amino‐2H‐azirines 1c–e with a 2‐propyl and 2‐propenyl substituent, respectively, at C(2), a 4,5‐dihydro‐1,2,4‐triazin‐3(2H)‐one of type 4 is formed as minor product (Scheme 3 and Table 1). Independent syntheses of these products proved the structure of 4. Several reaction mechanisms for the formation of compounds 3 and 4 are discussed, the most likely ones are described in Scheme 4: reaction of 2 as an NH‐acidic compound leads, via a bicyclic zwitterion of type A, to 3 as well as to 4. In the latter reaction, a ring‐expanded intermediate B is most probable.
Boscialin and Boscialin 4′‐O‐Glucoside, Two New Compounds Isolated from the Leaves of Boscia salicifolia OLIV
Authors: Pauli Niklaus , Séquin Urs , Walter Angelika 
Published: December 2004

AbstractBoscialin (1), a new compound structurally related to the ionones and abscisic acid, and its 4′‐O‐glucoside 2 were isolated from the MeOH extract of the leaves of the African medicinal plant Boscia salicifolia. The structures of the two compounds were determined mainly by NMR spectroscopy and by acid hydrolysis of the glycoside.
Conformation Analysis of the 8‐Membered Ring of 12H‐Dibenzo [d, g] [1, 3, 2] dioxathiocines: Symmetric and Asymmetric Conformations
Authors: Hug P. , Kolly Sandra , Meier Hansrudolf , Pitteloud Rita , Poppinger Dieter , Rihs Grety , Rist Günther 
Published: December 2004

AbstractThe 12H‐dibenzo [d, g] dioxathiocines 2 and 4 are prepared by condensation of the corresponding bis[phenols] 1 and 3 with SOCl2 and SCl2, respectively. X‐Ray analysis reveals the presence of the boat‐chair (BC) form as the only conformer in the solid state of the cyclic thiodioxy derivative 4a, whereas the sulfinyldioxy compound 2a exists in the asymmetric axial boat (B) form, i. e. with endo (axial) orientation of the exocyclic O‐atom. Conformational analysis using 1H‐NMR spectroscopy indicates the presence of a boat form for compounds 2, whereas compounds 4 again exist in the boat chair form. A comparison of 1H‐NMR and thermodynamic parameters with those of the cyclic sulfinyldioxy compound 5 with an equilibrium between e‐BC and a‐BC form (i.e. BC form with equatorial and axial orientation of the exocyclic O‐atom) is made.
Acid‐Promoted Rearrangements of N‐Substituted 8‐Oxa‐3‐azatricyclo[3.2.1.02′4] octane‐6,7‐dicarboxylates: Remote Substituent Effects on the Regioselectivity of the N‐Acylaziridine/Dihydrooxazone Rearrangement
Authors: Allemann Susy , Reymond Jean‐Louis , Vogel Pierre 
Published: December 2004

AbstractPreparations of dimethyl (1RS,2SR,4RS,5SR,6SR,7RS)‐ and dimethyl (1 RS,2SR,4RS,5SR,6RS,7SR)‐8‐oxa‐3‐azatricyclo[3;2.1.024] octane‐6,7‐dicarboxylate 15 and18, resp.) and of their N‐(tert‐butyloxy)carbonyl (14, 17) and V‐benzoyl (16, 19) derivatives are described. While treatment with nucleophilic acids (HCl, HBr. AcOH) of the exo, exo‐diesters 14 and 16 gave the corresponding products 23–27 of aziridine trans ‐addition, the exo, endo ‐diesters 17 and 19 led to the corresponding amino‐lactones 63 (methyl (1RS,2RS,3SR,6RS,7SR,9RS)‐2‐{[(tert‐butyloxy)carbonyl] amino}‐5‐oxo‐4,8‐dioxatricyclo[4.2.1.0 37] nonane‐9‐carboxylate) and 64 (methyl (1RS,2RS,3SR,6RS,7SR,9SR)‐2‐(benzoylamino)‐5‐oxo‐4,8‐dioxatricyclo[4.2.1.0 3′7] (nonane‐9‐carboxylate). Under non‐nucleophilic acidic conditions, the N‐benzoylaziridine 16 was rearranged quantitatively into dimethyl (1RS,2SR,26SR,67SR,7SR,8SR,9SR)‐4‐phenyl‐5,10‐dioxa‐3‐azatricyclo[4.3.1.02′7] dec‐3‐ene‐8,9‐dicarboxylate(31), and 19 into dimethyl (1RS,2SR,26SR,67SR,7SR,8SR,9SR)‐4‐phenyl‐3,10‐dioxa‐5‐azatricyclo [5.2.1.02′6] dec‐4‐ene‐8,9‐di‐carboxylate (65). Possible mechanisms of these highly selective reactions and rearrangements are discussed.