bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemie von α‐Aminonitrilen. Aziridin‐2‐carbonitril, ein Vorläufer von rca‐O3‐Phosphoserinnitril und Glycolaldehyd‐phosphat
Authors: Wagner Ernst , Xiang Yi‐Bin , Baumann Karl , Gück Jürgen , Eschenmoser Albert 
Published: December 2004

Chemistry of α‐Aminonitriles. Aziridine‐2‐carbonitrile, a Source of Racemic O′‐Phosphoserinenitrile and Glycolaldehyde PhosphateRacemic aziridine‐2‐carbonitrile (rac‐1) in MeCN solution reacts regioselectively (> 90%) with 2 equiv. of TsOH at room temperature to form the hydrotosylate of racemic O3‐tosylserinenitrile (rac‐2) via β‐ring opening (Scheme 2). A similar regioselective reaction takes place between rac‐l and H3PO4 to produce racemic O3‐phosphoserinenitrite (rac‐3) which is in turn a source of glycolaldehyde phosphate (=formylmethyl dihydrogenphosphate) under the conditions of a ‘retro‐Strecker’ reaction in aqueous solution (Scheme 6). These experiments document a close structural relationship between the simplest of the sugar phosphates and an α‐aminonitrile precursor. The English Footnotes (*) referring to Schemes 1‐7 are intended to provide an extension of this summary.
Elektrophile Substitutionsreaktionen des 1,1‐Difluoro‐1H‐cyclopropabenzols
Authors: Neidlein Richard , Kohl Matthias 
Published: December 2004

Electrophilic Substitution Reactions of 1,1‐;Difluoro‐1H‐cyclopropabenzene1,1‐Difluoro‐1H‐cyclopropabenzene (1) can be deprotonated with strong bases at C(2). The resulting 1,1‐di‐fluoro‐2‐lithio‐1H‐cyclopropabenzene (2) reacts with electrophiles to form C(2)‐substituted derivatives of 1. The Diels‐Alder reactions with electron‐poor dienes, characteristic for 1H‐cyclopropabenzene, do not occur with the 1,1‐difluoro analogue 1.
Eine Synthese methylierter Epoxyhydroazulenone durch intramolekulare [4 + 3]‐Cycloaddition einer aus 1,1‐Dichloro‐6‐(3‐methylfur‐2‐yl)hexan‐2‐on erzeugten Oxyallyl‐Zwischenstufe
Authors: Kaiser Roland , Föhlisch Baldur 
Published: December 2004

A synthesis of Methylated Epoxyhydroazulenones by Intramolecular [4 + 3] Cycloaddition of an Oxyallyl Intermediate, Generated from 1,1‐Dichloro‐6‐(3‐methyl‐2‐furyl)hexan‐2‐one(Z)‐3‐Methylpent‐2‐en‐4‐yn‐1‐ol (7) was transformed to 2‐(4‐chlorobutyl)‐3‐methylfuran (4b) and 2‐(but‐3‐enyl)‐3‐methylfuran (10a) by C‐alkylation and 5‐exo‐dig cyclization. The Grignard derivative formed from 4b gave 1,1‐dichloro‐6‐(3‐methylfur‐2‐yl)hexan‐2‐onc (1b) on reaction with dichloroacetyl chloride. This dichloromethyl ketone undergoes a base‐induced cyclization to form diastereoisomeric 7‐chloro‐1,2,3,6,7,8a‐hexahydro‐4‐methyl‐8H‐3a,6‐epoxyazulen‐8‐ones (3bα and 3bβ) by way of an intramolecular [4+3] cycloaddition of an oxyallyl intermediate 2b. By dechlorination and hydrogenation of 3bβ, the tricyclic hydroepoxyazulenones 18 and 19 have been synthesized.
Stereoelectronic Aspects of the Anomeric Effect in Fluoromethylamine
Authors: Irwin John J. , Ha Tae‐Kyu , Dunitz Jack D. 
Published: December 2004

AbstractHigh‐level ab initio calculations have been made for fluoromethylamine to study structural and energetic effects of the relative orientation of the N lone pair to the CF bond. The anti‐conformer (N lone pair anti‐planar to the CF bond) corresponds to the global energy minimum. It has the longest CF distance, the shortest CN distance, and is 7.5 kcal·mol−1 more stable than the related perpendicular conformation (lone pair perpendicular to the CF bond). The syn‐conformation also shows hallmarks of the anomeric effect: long CF bond, short CN bond, and energetic stability when allowance is made for the two pairs of eclipsed hydrogens. The transition state for N inversion is close to the syn‐structure; rotation about the CN bond is strongly coupled with this inversion process. Small bond distance changes of ca. 0.02 Å between parallel and perpendicular conformations are associated with dissociation energy differences of ca. 30 kcal·mol−1. Various criteria for assessing the strength of the anomeric effect are discussed.
Enzyme‐Mediated Regioselective Acylations of Flavonoid Disaccharide Monoglycosides
Authors: Danieli Bruno , De Bellis Paolo , Carrea Giacomo , Riva Sergio 
Published: December 2004

AbstractFlavonoid disaccharide monoglycosides have been acylated by the catalytic action of the protease subtilisin in anhydrous pyridine. The effects of the nature of the sugars and of the interglycosidic bonds on the regioselectivity of the reactions have been analyzed. The selectivity was excellent with rutin (1), hesperidin (2), naringin (6), and quercetin 3‐O‐[O‐(β‐D‐glucopyranosyl)‐(1→4)‐α‐L‐rhamnoside] (9), giving single monoesters on their glucose moieties (see la, 2a, 6a, and 9b, resp.); quite interestingly, in the last compound, acylation did not occur at the free primary OH group but at the secondary OHC(3‴). On the other hand, a mixture of mono‐ and diesters was obtained with the flavonoid peltatoside (7).
A Novel Type of Dimeric Secoiridoid Glycoside from Lisianthius jefensis ROBYNSet ELIAS
Authors: Hamburger Matthias , Hostettmanna Maryse , Stoeckli‐Evans Helen , Soils Pablo N. , Gupta Mahabir P. , Hostettmanna Kurt 
Published: December 2004

AbstractA dimeric secoiridoid glucoside named lisianthioside (l) has been isolated from the roots of Lisianthius jefensis ROBYNS et ELIAS (Gentianaceae). The structure was established by spectroscopic analysis (UV, IR, 1H‐ and 13C‐NMR, DCI‐MS) of glycoside 1, peracetate 1a, aglycone 3 and the dimethoxy derivatives 4a–c. Lisianthioside (1) is the first representative of a novel type of dimeric secoiridoids. Biogenetically derived from two sweroside (2) moieties, the tricyclic aglycone features a symmetrical 12‐membered bislactone ring. In contrast to the moderately bitter sweroside (2), lisianthioside (1) is tasteless.
Circular Dichroism of Some 2‐(Phenylmethyl)pyridine Derivatives
Authors: Berova Nikolina , Eojadziev Stefan , Bresciani‐Pahor Nevenka , Ivanova Petko M. , Kojić‐Prodicć Biserka , Rakovska Rositza , Ružić‐Toroš ŽIva , Snatzke Günther 
Published: December 2004

AbstractThe absolute configuration of the 2‐(phenylmethyl)pyridine derivatives 1–9 had been established by X‐ray diffraction and chemical correlation. Their CD spectra have been studied in different solvents for the free and protonated forms. It has now been found that, from the sign of the strong CD couplet between 270 and 220 nm, which was observable for all these compounds besides 7 and 9, their absolute configuration can be determined much quicker.
Synthèse énantiospécifique du (+)‐(6S, 8R, E)‐2,3‐didéhydrononactate de méthyle
Authors: Deschenaux Pierre‐François , Jacot‐Guillarmod André 
Published: December 2004

Enantiospecific Synthesis of (+)‐(6S,8R,E)‐Methyl 2,3‐Didebydrononactate(+)‐(6S,8R,E)‐Methyl 2,3‐didehydrononactate (7) has been synthesised from (−)‐(3R)‐methyl 3‐hydroxy‐butanoate with an enantiomeric excess ≥95%. The known stereoselective hydrogenation of 7 affords (−)‐(2R,3R,6S,8R)‐methyl nonactate (8) as the major isomer, a chiral synthon for the synthesis of nonactin.
Synthesis and Configuration of Some Hydroxymilbemycin Derivatives Including 22,23‐Dihydroavermectin B1b Aglycone
Authors: Frei Bruno , Huxley Philip , Maienfisch Peter , Mereyala Hari Babu , Rist Günther , O'Sullivan Anthony C. 
Published: December 2004

AbstractThe synthesis of several configurationally defined hydroxymilbemycin derivatives is described. One of these allylic alcohols is the known 5‐O‐[(tert‐butyl)dimethylsilyl]‐13α‐hydroxymilbemycin D (= 5‐O‐[(tert‐butyl)‐dimethylsilyl]‐22,23‐dihydroavermectin B1b, aglycone; 15D), the synthesis of which represents LI conversion of the milbemycin to the avermectin series of natural products. The configurations at C(13), C(14), and C(15) of the new milbemycin derivatives were determined by NMR experiments and force‐field calculations.
Synthese und chemische Eigenschaften heterocyclischer Tetracyanodimethane eines heterocyclischen N,N′‐Dicyanodiimins sowie von voll substituierten monocyclischen Tetracyanodimethanen
Authors: Neidlein Richard , Bischer Alfred 
Published: December 2004

Syntheses and Chemical Properties of Heterocyclic Tetracyanodimethanes of a Heterocyclic N,N′‐Dicyanodiimine and of Fully Substituted Monocyclic TetracyanodimethanesIn the presence of different bases, 4,8‐diethoxy‐3H,7H‐benzo[1,2‐c:4,5‐c′]diisoxazole‐3,7‐dione (3) reacts with malonodinitrile or β‐oxobenzenepropanenitrile to the coloured salts 4a,b and 5, respectively, which are alkylated to the tetracyanoquinodimethane‐like heterocycles 2a,b and to the bis [benzoyl(cyano)methylidene]‐substituted heterocycle 6 (Scheme 1). Hydrogenation of 2a,b affords the fully substituted 7a,b, and with 2‐(1,3‐dithiol‐2‐ylidene)‐1,3‐dithiole, 2a gives the 1:1 charge‐transfer complex 8. Heterocyclic quinone 9 is transformed to the monocyarioimino derivative 10, and 3 reacts with cyanamide and NaH to the N,N′‐dicyanodiimine salt 12.
The Radical Anions of [2.2]Metaparacyclophane‐1,9‐diene and Some Derivatives: An ESR and ENDOR Study
Authors: Bruhin Jürg , Buser Urs , Gerson Fabian , Wellauer Thomas 
Published: December 2004

AbstractThe radical anion of [2.2]metaparacyclophane‐1,9‐diene (1) has been fully characterized by its hyperfine data with the use of ESR, ENDOR, and TRIPLE‐resonance spectroscopy. Assignments of all proton‐coupling constants are based on comparison with the spectra of the radical anions of the 8‐deuterio‐, 1,2,9,10‐tetradeuterio‐, and 1,10,12,13,15,16‐hexadeuterio derivative. The spin distribution in 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} drastically differs from that in the radical anion of [2.2]metaparacyclophane (4), and it is not readily interpreted by semi‐empirical MO‐methods. The radical anions of 8‐fluoro‐ (2) and 8‐cyano[2.2]metaparacyclophane‐1,9‐diene (3) have also been investigated. Substitution of 1 by an F‐atom in the ‘exposed’ 8‐position, to yield 2, has only a minor effect on the π‐spin distribution in the radical anion, as evidenced by the similar proton‐hyperfine data for 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} and 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}. The 19F‐coupling constant for 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} is much smaller than expected, thus indicating a pronounced ‘ortho‐effect’ in the pertinent position. The ESR and ENDOR spectra of 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} in 1,2‐dimethoxyethane (counterion K+) reveal an equilibrium between a tightly and a loosely ion‐paired radical anion. Whereas the former is present exclusively in 2‐methyltetrahydrofuran (K+), the latter prevails in N,N‐dimethylformamide (Et4N+) and in mixtures of 1,2‐dimethoxyethane with N,N′,N,N″,N,′N″‐hexamethylphosphoric triamide (K+). The high temperatures required for the conformational flipping of the meta‐bridged benzene ring in 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document}, and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\scriptstyle {{\relbar}\kern-4pt {.} }} $\end{document} to be fast on the hyperfine time‐scale are well above the range appropriate for the studies of these radical anions.
Photo‐Cleavable Cryptands: Synthesis and Structure
Authors: Warmutha Ralf , Grell Ernst , Lehn Jean‐Marie , Bats Jan W. , Quinkert Gerhard 
Published: December 2004

AbstractThe four photo‐cleavable ligands 1–4 of the macrobicyclic‐cryptand type have been synthesized by introducing a photo‐sensitive 2‐nitrobenzyl‐ or 4,5‐dimethoxy‐2‐nitrobenzyl‐ether bond into one of the bridges. These compounds are expected to retain the selective binding features of the parent cryptands and to allow the photolytically induced release of alkali ions in aqueous solution. The crystal structures of the ligand 5‐(2‐nitro‐phenyl)‐4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane (3) and of its KSCN complex 13 have been determined. They are analogous to those of the corresponding parent species, confirming the macrobicyclic geometry and the cryptate nature of the complex. Spectroscopic properties are reported.
α‐D‐Glycosyl‐Substituted α,α‐D‐Trehaloses with (1 → 4)‐Linkage: Syntheses and NMR Investigations
Authors: Wessel Hans Peter , Englert Gerhard , Stangier Peter 
Published: December 2004

AbstractTwo symmetrical trehalose glycosyl ‘acceptors’ 4 and 6 were prepared and three of the unsymmetrical type, 8, 10, and 11. Glucosylation of symmetrical ‘acceptor’ 4 gave a higher yield of trisaccharide (44%) than protect ve‐group manipulation, namely via selective debenzylidenation 2 → 9 or monoacetylation 2 → 5 which proceeded in moderate yields (33–34%). A comparison of catalysts in the cis‐glucosylation of trehalose ‘acceptor’ 10 with tetra‐O‐benzyl‐β‐D‐glucopyranosyl fluoride 13 profiled triflic anhydride ((Tf)2O) as a new reactive promoter yielding 92% of trisaccharide 14, deblocking gave the target saccharide α‐D‐glucopyranosyI‐(1 → 4)‐α,α‐D‐trehalose. 1H‐NMR spectra of most compounds were analyzed extensively. The use of the ID TOCSY technique is advocated for its time efficiency, if needed supplemented by ROESY experiments.
Diels‐Alder Reactions of (1H‐Indol‐3‐yl)‐enacetamides and ‐endiacetamides: A Selective Access to Acetylamino‐Functionalized [b]Annelated Indoles and Carbazoles
Authors: Pindur Ulf , Otto Christian , Molinier Michel , Massa Werner 
Published: December 2004

AbstractDiels‐Alder reactions of the (1H‐indol‐3‐yl)‐enacetamides and ‐endiacetamides 1a–d with some carbodieno‐philes and 4‐phenyl‐3H‐1,2,4‐triazole‐3,5(4H)‐dione give rise to the novel amino‐functionalized carbazole; 4–6 and 8 (Scheme 3). Ethenetetracarbonitrile reacts with 1b to furnish the Michael‐type adduct 7 (Scheme 3). Structural aspects of the starting materials 1, which exhibit above all 3‐vinyl‐1H‐indole reactivity, are discussed with regard to the prediction of a Diels‐Alder process.
Physovenines: Efficient Synthesis of (−)‐ and (+)‐Physovenine and Synthesis of Carbarnate Analogues of (−)‐Physovenine. Anticholinesterase Activity and Analgesic Properties of Optically Active Physovenines
Authors: Yu Qian‐sheng , Liu Chi , Brzostowska Margareth , Chrisey Linda , Brossi Arnold , Greig Nigel H. , Atack John R. , Soncrant Timothy T. , Rapoport Stanley I. , Radunz Hans‐Eckart 
Published: December 2004

AbstractColumn chromatography of easy available (±)‐physovenine (2) on cellulose triacetate afforded (−)‐ and (+)‐physovenine (2a and 2b, resp.). Alkaloids 2a, b required for pharmacological testing were prepared from eserolincs (3a, b) by an improved procedure. Natural (−)‐physovenine (2a) was equally potent in inhibiting AChE and BChE in vitro as natural physostigmine (1a), and twice as potent as the unnatural antipode 2b against AChE and 14 times as potent against BChE. Several carbamate analogs of 2a were at least as potent as the former compound in these assays. None of the compounds tested did bind to different opiate receptor or serotonine receptor preparations. Most of the compounds tested had considerable analgesic activity in the Writhing test.
Asymmetric Synthesis of Diazepino‐β‐lactams by [2 + 2] Cycloaddition of an ‘Evans‐Sjogven’ Ketene with 1H‐1,2‐Diazepines
Authors: Muller Marc , Bur Daniel , Tschamber Théophile , Streith Jacques 
Published: December 2004

AbstractThe ketene derivative of the chiral oxazolidinone 1 underwent non‐concerted stereo specific [2 + 2] cycloadditions with the (Z)‐imine moiety of diazepines 2, leading thereby with good diastereoselection to the trans‐β‐lactam adducts 3 (major) and 4 (minor). The absolute configuration of the major cycloadduct 3a was determined by an X‐ray analysis. Its formation is discussed in terms of minimisation of steric interaction in the two transition states which give sequencially the zwitterionic intermediates and the final cycloadducts.
Conformational Analysis of Marine Polyhalogenated β‐Chamigrenes Through Temperature‐Dependent NMR Spectra
Authors: Guella Graziano , Chiasera Giuseppe , Mancini Ines , Pietra Francesco 
Published: December 2004

AbstractTemperature‐dependent 1H‐ and 13C‐NMR spectra reveal that polyhalogenated marine β‐chamigrenes or synthetic derivatives thereof which are trans‐diequatorially, substituted at C(8) and C(9), such as rogiolol ((−)‐2), obtusol ((+)‐3), and their acetates (+)‐1 and (−)‐4, undergo slow ring‐A chair‐chair inversion. Conformational equilibria and kinetics are investigated with the aid of synthetic model compounds and molecular‐mechanics calculations. Thus, steric repulsions between Brax–C(2) and Heq–C(7) are seen to disfavour thermodynamically conformers 1b, 2b, 3b, and 4b, which can only be detected through cross‐saturation transfer, while additional steric repulsions between Meax–C(1) and OHax–C(3) make conformer 8b of obtusol epimer so scarcely populated that it can not be detected. In agreement, with (+)‐9 and (+)‐10, which have a trigonal C(2), two conformers can be directly observed by NMR. The kinetic barriers, which are seen to arise mainly from steric repulsions between Hax–C(14) and the axial H or halogen atoms at C(8) and C(10), are calculated and discussed with respect to well documented exocycliemethylidene‐substituted cyclohexane(ene) systems. This helps to rationalize why in rogiolol acetate ((+)‐1) ring B is unusually inert towards Zn/Et2O/AcOH which causes bromohydrine‐group elimination from ring A.
Synthèse des (−)‐(6R)‐et(+)‐(6S)‐tétrahydro‐6‐[(Z)‐pent‐2‐ényl]‐2H‐pyran‐2‐one, lactones de Jasminum grandiflorum L. et de Polianthes tuberosa L.
Authors: Blaser Florian , Deschenaux Pierre‐François , Kallimopoulos Thomas , Jacot‐Guillarmod André 
Published: December 2004

Synthesis of (−)‐(6R)‐ and (+)‐(6S)‐Tetrahydro‐6‐[(Z)‐pent‐2‐enyl]‐2H‐Pyran‐2‐one, lactones from Jasminum grandiflorum L. and from Polianthes tuberosa L.(−)‐(2S)‐Ethyl 2‐hydroxyhexanedioate ((2S)‐2) was obtained by kinetic resolution of racemic ethyl 2‐hydroxy‐hexanedioate with baker's yeast. The key intermediates (+)‐(5R)‐ and (−)‐(5S)‐ethyl 5,6‐epoxyhexanoate ((5R)‐ and (5S)‐6, resp.) are proved to be useful synthons for the total synthesis of chiral 6‐alkyl‐δ‐lactones, as exemplified by the preparation of both enantiomers of jasmine lactone ((6R)‐ and (6S)‐10, resp.).
Novel Antifungal Tetracyclic Compounds from Bauhinia rufescens LAM.
Authors: Maillard Marc P. , Recio‐Iglesias Maria‐Carmen , Saadou Mahamane , Stoeckli‐Evans Helen , Hostettmann Kurt 
Published: December 2004

AbstractAs the root bark CH2Cl2 extract of Bauhinia rufescens showed antifungal activity in a bioassay with the plant pathogenic fungus Cladosporium cucumerinum, a phytochemical investigation was undertaken on material collected in Niger. Activity‐guided fractionation of this extract, using different preparative chromatographic methods, allowed the isolation of the four new antifungal tetracyclic compounds 1–4. Their structures were established by 1H‐ and 13C‐NMR data, and single‐crystal X‐ray analyses were used to confirm the structures of 1 and 3. The isolated compounds seem to be biogenetically related to a stilbene.
Nucleotides. Part XXXV. Synthesis of 3′‐deoxyadenylyl‐(2′–5′)‐3′‐deoxyadenyIyl‐(2′–ω)‐9‐(ω‐hydroxyalkyl)adenines
Authors: Mikhailov Sergey N. , Charubala Ramamurthy , Pfleiderer Wolfgang 
Published: December 2004

AbstractVia the phosphotriester approach, new structural analogs of (2′–5′)oligoadenyiates, namely 3′‐deoxyadenylyl‐(2′–5′)‐3′‐dcoxyadenylyl‐(2′–ω)‐9‐(ω‐hydroxyalkyl)adenines 18–21, have been synthesized (see Scheme) which should preserve biological activity and show higher stability towards phosphodiesterases. The newly synthesized oligonucleotides 18–21 have been characterized by 1H‐NMR spectra, TLC, and HPLC analysis.
Nucleotides. Part XXXVI. Syntheses and biological characterization of phosphorothioate analogues of (3′–5′)adenylate trimer
Authors: Chambala Ramamurthy , Sobol Robert W. , Kon Ning , Suhadolnik Robert J. , Pfleiderer Wolfgang 
Published: December 2004

AbstractThe four protected diastereoisomcrs 7a/7b and 8a/8b P‐thioadenylyl‐(3′–5′)‐P‐thioadenylyI‐(3′–5′)‐adenosine were synthesized, separated, and deblocked to the free oligonucleotides (Scheme). Biochemical characterization of these (3′–5′)phosphorothioate analogues of adenyiate trimer indicate that these compounds, and the corresponding 5′‐monophosphates, neither bind to nor activate RNase L, and are considered to be valuable control compounds in screening experiments.
Dipeptide Derivatives with a Phosphonate Instead of Carboxylate Terminus by C‐Alkylation of Protected (Decarboxy‐dipeptidyl)phosphonates
Authors: Gerber Christian , Seebach Dieter 
Published: December 2004

AbstractZ‐Protected diphenyl (decarboxy‐dipeptidyl)phosphonates 5a‐c with a (decarboxysarcosinyl)phosphonate moiety are prepared from Z‐L‐alanine (1a). Z‐L‐valine (1b), and Z‐L‐phenylalanine (1c) by the following series of steps: coupling with methyl sarcosinate (→2a–c), saponification (→3a–c), Hofer‐Moest oxidative decarboxyiation by electrolysis in MeOH (→4a–c), and Arbuzov reaction with P(OPh)3/TiCl4 (Scheme 3). Double deprotonation and alkylation lead to non‐stereoselective incorporation of side chains next to the phosphonate group (products of type 6–8, nine examples, see Scheme 4). In the cases of 6a–c and 8c, the diastereoisomers could be separated and the configuration of the newly formed stereogenic center deduced. We assign the L,D‐configuration to the diastereoisomers for which the 31P‐NMR signal appears at higher field.
The chemistry of coumarin derivatives. Part 3. Synthesis of 3‐alkyl‐4‐hydroxycoumarins by reductive fragmentation of 3,3′‐alkyiidene‐4,4′‐dihydroxybis[coumarins]
Authors: Appendino Giovanni , Cravotto Giancarlo , Tagliapietra Silvia , Ferraro Stefano , Nano Gian Mario , Palmisano Giovanni 
Published: December 2004

AbstractTreatment of 3,3′‐alkylidene‐4,4′‐dihydroxybis[coumarins] 1 with NaBH3CN in refluxing MeOH affords 3‐alkyl‐4‐hydroxycoumarins 2 and 4‐hydroxycoumarin (3; Scheme 1). The reaction might take place via hydride trapping of alkylidenechromandiones C formed from 1 in a retro‐Michael reaction. Such a retro‐Michael reaction of 1 might be biologically relevant. The presence of C during the reductive fragmentation 1 → 2 is suggested by Diels‐Alder and nucleophilic trapping of the alkylidenechromandiones C as well as from cross‐over experiments with coumarins other than 3 (see Scheme 2). The reductive fragmentation of 1 allows the chemo‐ and regioselective synthesis of a variety of 3‐alkyl‐4‐hydroxycoumarins 2 (see Table).
The Reaction of 1,2:3,4‐Diepoxy‐2,3‐dimethylbutane with Nucleophiles
Authors: Farkas Frédéric , Wellauer Thomas , Esser Thomas , Séquin Urs 
Published: December 2004

AbstractTo find out whether the 1,4‐addition to 1,2:3,4‐diepoxides, which so far has been observed only once, is of a more general character, we investigated the reaction of a variety of O‐, C‐, N‐, and S‐nucleophiles with the model compound 1,2:3,4‐diepoxy‐2,3‐dimethylbutane (Scheme 4). In several cases, 1,4‐addition products could, indeed, be observed besides the expected 1,2‐adducts (Table).