bluuebunny/crossref_metadata_2025_split huggingface dataset:
Azo Bridges from Azines, XXIII. 1,5‐Laticyclic Conjugation Between Parallel Azo and o‐Phenylene Bridges. Structure Dependence of [6 + 2] Photocycloadditions
Authors: Beck Karin , Brand Uwe , Hünig Siefried , Martin Hans‐Dieter , Mayer Bernhard , Peters Karl , von Schnering Hans Georg 
Published: July 2007

AbstractExamples were synthesized of the four systems 1, 3, 5, and 7, in which rigid parallelo o‐phenylene and azo bridges are connected to five‐ and/or six‐membered carbocyclic moities. The o‐phenylene bridge was introduced by two routes: (A) starting from precursors already containing that bridge (24, 29) and assembling the azo bridge in consecutive steps (→ 3a, 3b, 5c, 5d, 5e, 5f, 5g); (B) starting from the systems with parallel CC/NN bridges (9a, 11a, 13a, 42) and completing the dihydro‐o‐phenylene ring by tetrachlorothiopene dioxide. Dyotropic hydrogen transfer of the azo bridge enhances the dehydrogenation of the intermediate dihydro‐o‐phenylene derivatives (22, 3cH2, 25). This mechanism was proved by the domino hydrogen transfer 44 → 45 → 5h. Via route B, systems 1a, 1b, 3c, 3d, 5a, 5b, 5h, and 43 were obtained. In sharp contrast to the smooth [2 + 2] photocycloaddition of systems 9, 11, 13, and 15 (CC/NN bridges), [6 + 2] photocycloaddition occurs only with systems 1 and (5C/5N) and 3 (6C/5N) but not with systems 5 (5C/6N) and 7 (6C/6N). These differences are not caused by slightly varying distances of the two bridges (X‐ray data) but by the higher n_ ionization energy of the azo group incorporated into a 2,3‐diazabicyclo[2.2.1]hept‐2‐ene (DBH) instead of a 2,3‐diazabicyclo[2.2.2]oct‐2‐ene (DBO) moiety, the hypsochromicity of the corresponding DBH n‐π* state and the higher ground‐state energy of DBH compared to DBO.
Pheromone Synthesis, CLXXVII. Synthesis of the Enantiomers of 2‐Methyl‐4‐heptanol and 2‐Methyl‐4‐octanol, the Pheromone Components of the West Indian Sugarcane Borer
Authors: Takenaka Motonobu , Takikawa Hirosato , Mori Kenji 
Published: July 2007

AbstractBoth the enantiomers of 2‐methyl‐4‐heptanol (1) and 2‐methyl‐4‐octanol (2), the components of the male‐produced aggregation pheromone of the West Indian sugarcane borer (Metamasius hemipterus), were synthesized by starting from the enantiomers of leucine.
Enantioselective Total Synthesis and Absolute Configuration of the Natural Norsesquiterpene 7‐Demethyl‐2‐methoxycalamenene by a Silane‐Terminated Intramolecular Heck Reaction
Authors: Tietze Lutz F. , Raschke Thomas 
Published: July 2007

AbstractThe total synthesis of the norsesquiterpene 7‐demethyl‐2‐methoxycalamenene (1) by a newly developed enantioselective silane‐terminated Heck reaction is described. The Pd0‐catalyzed transformation of the allylsilane 7, obtained from 3‐(3‐methoxyphenyl)propanol (2) in 7 steps, provides the tetralin 8 in 91% yield and with 92% ee in the presence of (R)‐BINAP. Transformation of 8 via 14 and 15 gives 1. The absolute configuration of 1 which has previously not been known was deduced from a single‐crystal X‐ray analysis of 10, obtained from the cyclization product 8 by hydroboration and acylation with camphanic acid chloride.
Chemical Reactions of the Stable Carbene 1,3,4‐Triphenyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐ylidene
Authors: Enders Dieter , Breuer Klaus , Runsink Jan , Henrique Teles J. 
Published: July 2007

AbstractThe title compound 1,3,4‐triphenyl‐4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐ylidene (1), a stable carbene, is chemically characterized via its reactivity towards a multitude of organic substrates. Its behaviour in insertion, addition and cycloaddition reactions allows its classification as a typical representative of nucleophilic carbenes.
Concave Reagents, 21. Selective Acylations of Primary and Secondary Alcohols by Ketenes
Authors: Schyja Wolfgang , Petersen Sönke , Lüning Ulrich 
Published: July 2007

AbstractConcave pyridines 1 were used to catalyze the addition of primary and secondary alcohols to ketenes 4, and the kinetic data of these catalyses were determined. In inter‐ and intramolecular competitions the use of 1e–g led to improved selectivities for the acylation of primary alcohols in comparison with secondary alcohols. All primary alcohols react at comparable rates. Observed rate constants were correlated with Taft's Es values. The starting materials and products were fully characterized.
Molecular Ribbons Containing Pyridine Rings
Authors: Breidenbach Stefan , Ohren Stefan , Herbst‐Irmer Regine , Kotila Sirpa , Nieger Martin , Vögtle Fritz 
Published: July 2007

AbstractThe first synthesis of the ribbon‐like compounds 6–10 is described. The new building block diethyl 2,6‐bis(bromomethyl)pyridine‐3,5‐dicarboxylate 1 was prepared and characterized. Single‐crystal X‐ray structure analyses indicate that these ribbon‐like molecules arrange in a folded conformation, with the pyridine and benzene units being folded in a face‐to‐face manner, and the tosyl units of 8–10 pointing outwards. The “intramolecular self‐assembly” (folding) of these molecular ribbons is primarily attributable to the energetically more favourable syn conformation of both the [3.3]metacyclophanes and the pyridinophanes.
Configuration of Enolates of β‐Ketocarboxylic Acid Esters — Carbocation‐Carbanion Salts
Authors: Meier Herbert , Buß Monika , Adam Martin 
Published: July 2007

AbstractDeprotonation of (Z)‐ or (E)‐3‐hydroxy‐2,3‐dimesitylpropenoic acid methyl ester (1a) with tetrakis(dimethylamino)‐methane (3) led to stable salt (E)‐2a, which belongs to a very rare species of salts that consist of a heteroatom‐stabilized carbocation and a heteroatom‐stabilized carbanion. An analogous guanidinium salt (E)‐2bwas formed in the reaction of 3‐oxo‐2,3‐diphenylpropanoic acid methyl ester (1b) and3. The molecular structures of these enolates were studied by NMR spectroscopy and an X‐ray analysis of (E)‐2a{MC[N(CH3)2]3} and compared with those of the corresponding alkali enolates.
Zur Rekombinationsenthalpie von Radikalen — Thermochemie der Ringöffnung von Cyclophanen
Authors: Roth Wolfgang R. , Hopf Henning , de Meijere Armin , Hunold Frank , Börner Sabine , Neumann Martin , Wasser Thorsten , Szurowski Jörg , Mlynek Cornelia 
Published: July 2007

Radical Recombination Enthalpy. — Thermochemistry of the Ringopening of CyclophanesBy thermolysis of the cyclophanes 1, 5, 8, 11, 14, 18, and 21 in the presence of NO or O2 the enthalpy profiles for the ring opening were determined from the temperature, NO, or O2 dependance of the trapping rates of the intermediate diradicals. The experimental enthalpy wells, which varied between 3 and 12 kcal · mol‐1, can be simulated well with a reaction forcefield making use of the EVBH method of Malrieu et al. This result gives confidence that also meaningful recombination barriers of radicals can be obtained by this method.
The Structure of Benzimidazole Cyanine Dyes, Their Spectroscopy and Their Performance in Photographic Emulsions
Authors: Peng Zheng‐Hong , Geise H. J. , Zhou Xiang‐Feng , Peng Bi‐Xian , Carleer R. , Dommisse R. 
Published: July 2007

AbstractThe multi‐step synthesis of two benzimidazole trimethine cyanines as possible green sensitizing dyes (Gs3‐1, Gs3‐2) is reported. Compounds were characterized from UV‐Vis, mass spectroscopic and NMR data. The charge density distributions of the two compounds, calculated using the semi‐empirical MOPAC 93 package, are in agreement with assignments in NMR spectroscopy. Sensitizing properties of the cyanine dyes were evaluated in actual photographic T‐grain emulsions.
Addition and Cycloaddition Reactions of Arenediazonium Ions with 1,3‐Dienes: A Shift From a Concerted to a Stepwise Mechanism
Authors: Hartnagel Manfred , Grimm Klaus , Mayr Herbert 
Published: July 2007

AbstractArenediazonium ions 1 undergo [2+ + 4] cycloadditions with (E)‐1,3‐pentadiene (2a), 2,3‐dimethylbutadiene (2b), and (E)‐2‐methyl‐1,3‐pentadiene (2c) to give dihydropyridazines or pyridazinium salts. While highly electrophilic diazonium ions and the unsymmetrical dienes 2a and 2c predominantly yield those regioisomers that are expected for a stepwise cycloaddition process, the opposite regioselectivity is found in the cycloadducts of less electrophilic diazonium ions. Kinetic investigations and product studies indicate that all cycloaddition reactions proceed concertedly. The dienes 2d and 2e, in contrast, undergo ordinary azo coupling reactions in acetonitrile/methanol with formation of the hydrazones 17 and the azo compounds 18, respectively. It is demonstrated that the linear free enthalpy relationship lgk = s (N + E) can also be used to roughly estimate the rates of ionic cycloaddition reactions.
Synthesis of Bromo‐iodo‐hydroquinone Monoalkyl Ethers
Authors: Höger Sigurd 
Published: July 2007

AbstractTwo methods for the preparation of 2‐bromo‐5‐iodo‐p‐alkoxyphenols and the isomeric 5‐bromo‐2‐iodo‐p‐alkoxyphenols are reported in detail. In both cases the key to successful synthesis is the use of the difference in ortho‐directing power of phenols, phenolethers and phenolesters. During the bromination of 2‐iodo‐4‐propyloxyphenyl acetate (5) an unexpected “iodo‐effect” was observed, which can be attributed to the high polarisibility of iodine.
A Tandem Claisen‐Decarboxylation‐Aldol Reaction – Facile Access to The Fredericamycin A Core
Authors: Baskaran Sundarababu , Nagy Edgar , Braun Manfred 
Published: July 2007

AbstractA tandem reaction of doubly deprotonated indanecarboxylic acid 3 with ethoxyphthalide 5 leads to the formation of the spirocyclic diastereomers 6a and the 6b in a ratio of 9:1. They are converted to the spirodiketone core 2 of fredericamycin A (1).
Pheromone Synthesis, CLXXVIII. – Synthesis of (−)‐exo‐Isobrevicomin and Its (−)‐endo Isomer, the Components of The Male‐Produced Volatiles of the Mountain Pine Beetle, Dendroctonus ponderosae
Authors: Mori Kenji , Takikawa Hirosato , Nishimura Yutaka , Horikiri Hiromasa 
Published: July 2007

Abstract(–)‐exo‐Isobrevicomin {(1S,5R,7S)‐(–)‐5‐ethyl‐7‐methyl‐6,8‐dioxabicyclo[3.2.1]octane (1)} and its (–)‐endo isomer [(1S,5R,7R)‐2] were synthesized by employing the acetylenic acetal 7 as the common intermediate and by using the Sharpless asymmetric dihydroxylation and lipase‐catalyzed acetylation as the key reactions.
Regiospecific Synthesis of 3,4‐Disubstituted Furans and Thiophenes
Authors: Ye Xin‐Shan , Yu Pe , Wong Henry N. C. 
Published: July 2007

AbstractThe regiospecific synthesis of 3,4‐disubstituted furans and thiophenes is reviewed. Our initial approach used 3,4‐bis(tri‐n‐butylstannyl)furan as a building block, which led to many structurally diverse 3,4‐disubstituted furans. Another avenue was explored by using 3,4‐bis(trimethylsilyl)furan and 3,4‐bis(trimethylsilyl)thiophene as precursors. A variety of unsymmetrically 3,4‐disubstituted furans and thiophenes were prepared in this way. The advantages of our strategy lie in its stepwise manner as well as its prospect of yielding 3,4‐disubstituted furans and thiophenes with rather different substitution pattern.
New Sesquiterpene Lactones and Other Constituents from Centaurea paui
Authors: Cardona Luz , García Begoña , Muñoz M. Carmen , Navarro Francisca I. , Pedro José R. 
Published: July 2007

AbstractAerial parts of Centaurea paui afforded, in addition to several known sesquiterpene lactones, the two new elemanolides 2–4, the new elemane derivative 5 as well as the five new heliangolides 14–18. Their structures were elucidated by spectroscopic methods, especially high‐field NMR spectroscopy. The structure of the heliangolide 12 previously isolated from this plant, has been confirmed by X‐ray diffraction.
Diastereoselective Synthesis of 1‐Hydroxy‐Substituted Benzo[b]quinolidines and 11‐Hydroxy‐Substituted Azepino[1,2‐b]isoquinolines via Hetero‐Ene Cyclization
Authors: Monsees Axel , Laschat Sabine , Kotila Sirpa , Fox Thomas , Würthwein Ernst‐Ulrich 
Published: July 2007

Abstract(L)‐Phenylalanine 4 can be converted to N‐(4‐methyl‐3‐pentenyl)tetrahydrosisoquinoline‐3‐carbaldehyde 10 and the corresponding homologous aldehyde 19 in 4 and 5 steps, respectively, by employing the Pictet–Spengler reaction as the key step. After Lewis acid catalyzed cyclization of 10 and 19 the cis‐configured 1‐hydroxybenzo[b]quinolizidine 21a and 11‐hydroxyazepino[1,2‐b]isoquinoline 22a were obtained with high diastereoselectivities. Compound 21a, which was characterized by X‐ray structure analysis, displays a fishbone pattern of endless zig‐zag chains connected via intermolecular hydrogen bonds in the solid state.
1,4,5,8‐Tetraazafulvalenes – A Convenient One‐Pot Synthesis and Their Conversion to Fused Ring Systems
Authors: Käpplinger Christian , Beckert Rainer , Günther Wolfgang , Görls Helmar 
Published: July 2007

AbstractCycloacylation of formamidine with bisimidoyl chlorides of oxalic acid yields the new 1,4,5,8‐tetraazafulvalenes 4 via dimerization of carbenoid intermediates. The high symmetry of the stable heterofulvalenes as well as their dye character is confirmed by NMR and UV/Vis spectral data. Whereas methylation of these substrates leads to a mixture of diastereomeric tetramethyl derivatives 9a, b, cyclization with thiophosgene or triethyl orthoformate gives mainly the fused‐ring derivatives of 2H‐imidazole 10 and 12a, b, respectively. In the case of 12a, the X‐ray crystal structure reveals the approximately ideal planarity of the central tetraazafulvalene subunit.
Flexible, Long‐Chain Alkanediamines as Building Blocks for Catenanes – Steric Hindrance of Circumrotation by Derivatization
Authors: Baumann Sven , Jäger Ralf , Ahuis Friedrich , Kray Bernd , Vögtle Fritz 
Published: July 2007

AbstractNew catenanes of the amide‐linked type, such as 11 with one macrocycle containing two (CH2)12 chains are synthesized from long‐chain alkanediamines in yields of up to 21%. Consequently, the preorganization afforded by fixed and angular building units – so far considered essential – proves not to be necessary. The new sulfonamide catenanes exhibit high conformational flexibility. However, the circumrotation of one of the macrocycles can be hindered by substitution with bipyridine units at the sulfonamide nitrogen.
Intramolecular Heck Reaction for the Synthesis of Isochromanes under Ambient and High pressure
Authors: Tietze Lutz F. , Burkhardt Olaf , Henrich Marielouise 
Published: July 2007

AbstractThe iodoarenes 9 and 10, bearing (E)‐ and (Z)‐alkene moieties, respectively, easily prepared by alkylation of the corresponding alcohols 7a–c and 8a–c with 2 iodobenzyl iodide, undergo intramolecular Heck reactions to give the isochromanes 12–15a–c in good yields. The selectivity of the reaction depends on the size of the substituent R in 9 and 10; increasing bulkiness of R leads to a decrease in diastereoselectivity and an increase in regioselectivity. High‐pressure experiments confirm the proposed mechanism and show that bromoarenes such as 11, which tend to be unreactive at ambient pressure, give good results when the cyclisation is performed under high pressure.
Secondary Metabolites by Chemical Screening, 36. Ulupyrinone and Ulufuranol: New Heteroaromatic Metabolites from Streptomyces spina
Authors: Henne Petra , Grabley Susanne , Thiericke Ralf , Zeeck Axel 
Published: July 2007

AbstractChemical Screening with extracts of Actinomycetes strains resulted in the detection, isolation, and structural elucidation of two new heteroaromatic secondary metabolites, named ulupyrinone (1) and ulufuranol (2), from Streptomyces spina (strain FH‐S 2144). The absolute configuration of ulufuranol (2) was determined by analysis of the CD spectra of its dibenzoate, 3, using the dibenzoate chirality rule.
Synthesis of an Epoxide‐ and Carbonate‐Containing 6‐/10‐Membered Bicyclodienediyne Analogue of the Neocarzinostaitin Chromophore
Authors: Ferri Fabiola , Brückner Reinhard 
Published: July 2007

AbstractThe monocyclo‐diendiyne → bicyclo‐trienediyne strategy for obtaining dienediyne models of the antitumor antibiotic neocarzinostatin chromophore (1) was extended from generating 6‐/11‐membered bicyclotrienediynes (e.g. 2 → 4) to generating the 6‐/10‐membered bicyclotrienediyne 5. In the preparatory steps (Scheme 2), the bistriflate 10 was successively coupled with alkynes 9 and 11. Via the dienediynediol and its subsequent oxidation with the Dess‐Martin periodinane, we obtained the monocyclic dienediyne keto aldehyde 13. Cyclization of 13 with low‐valent titanium afforded the bicyclotrienediyne 5 in 42% yield (Scheme 3). Compound 5 was converted in five steps – namely ketal cleavage, monosilylation of the resulting diol 14, asymmetric Sharpless epoxidation, desilylation and carbonate formation – into the dienediyne epoxycarbonate 3. The structure of the latter is more closely related to the neocarzinostatin chromophore than our earlier analogues.
Carbocyliccis‐[1.1.1]‐Tris‐σ‐homobenzenes – Syntheses by Triple Epoxide → Cyclopropane Conversions, Structural Data, [σ2s+σ2s+σ2s] Cycloreversions
Authors: Rücker Christoph , Müller‐Bötticher Hermann , Braschwitz Wolf‐Dieter , Prinzbach Horst , Reifenstahl Uwe , Irngartinger Hermann 
Published: July 2007

AbstractBy triple epoxide → cyclopropane transformation starting fromcis‐benzene trioxide the 3α,6α,9α‐tris(TIPS‐ethynyl) (1b), ‐tris(alkoxycarbonyl) (1d, e), ‐tricyano (1f), and ‐tris(ammoniomethyl) (1j) derivatives of the still elusive parentcis‐[1.1.1]‐tris‐σ‐homobenzene (1a) have been synthesized. Out of a number of carbon nucleophiles tested, a weakly basic mixed cyanocuprate of Li‐TIPS‐propyne proved the reagent of choice: Eliminations were largely avoided, thescylloDescriptorsscyllo, chiro, allo, cisare used as in inositol nomenclature; TIPS– =iPr3Si–.‐2,4,6‐tris(TIPS‐propargyl)cyclohexane‐1,3,5‐triol (13a), obtained in a stereoselective one‐pot threefold epoxide opening (up to 69%), allowed the pertinent functional group manipulations. The selectivity of the base‐induced triple cyclopropane ring closure in the flexible cyclohexane precursors strongly depends on the activating groups and is promoted by fixation of the“all‐axial”conformation as an adamantoid orthophosphate. The ΔG≠values determined for the generally neat 3σ → 3π isomerizations [28.5 (1e), 29.0 (1f), 22.6 (1j) kcal mol−1] are in line with concerted reaction courses ([σ2s+σ2s+σ2s]). For the trinitrile1fan X‐ray structure analysis confirmed a nearly planar cyclohexane ring and a relatively large cyclohexane/cyclopropane interplanary angle (113°).
Reaction of α‐Hydroxyamino Ketones with Dicarbonyl Compounds – Synthesis of Imidazoline Nitroxides with a Functional Group in a Side Chain
Authors: Reznikov Vladimir A. , Volodarsky Leonid B. 
Published: July 2007

AbstractThe reaction of α‐hydroxyamino ketones 1 with diacetyl, acetyl acetone or acetoacetic ester in the presence of ammonium acetate results in the formation of 3‐imidazoline derivatives 2, which are precursors for the synthesis of stable nitroxides 8, 9, 14, 16, 17, 23–24 with various functional groups in the side chain at the 2‐position of the heterocycle.
Chemical, Enzymatic and Structural Studies in Molecular Glycobiology
Authors: McGarvey Glenn J. , Wong Chi‐Huey 
Published: July 2007

AbstractCarbohydrates are increasingly appreciated for their critical roles in biological functions. Driving these studies addressing the molecular basis of carbohydrate‐mediated events is the availability of natural and unnatural carbohydrates. Recently, new methods of enzymatic synthesis have been developed that now afford rapid access to complex, structurally diverse oligosaccharides on large scales. This methodology has been essential to gaining insight into the molecular details of important carbohydrate recognition phenomena that are associated with many signaling processes. This review summarizes recent chemical studies examining selectin/sialyl Lewisxbinding, a key event in inflammation and metastasis, and describes the development of carbohydrate mimetics that may offer leads to new therapeutic agents. In addition, combinatorial synthesis has been used to prepare carbohydrate mimetics to neomycin B, an aminoglycoside that binds RNA involved in HIV infection, and chemoenzymatic methodology has been applied to the design and synthesis of mechanism‐based inhibitors of glycoprocessing enzymes.
Saturated Heterocycles, 252. Synthesis and Stereochemistry of Stereoisomeric 6‐Methyl‐Substituted Pyrimido[6,1‐a]Isoquinolines
Authors: Fülöp Ferenc , Tari János , Bernáth Gábor , Sohár Pál , Dancsó András , Argay Gyula , Kálmán Alajos 
Published: July 2007

AbstractStereoisomeric (1R*,3R*)‐ and (1R*,3S*)‐6,7‐dimethoxy‐3‐methyl‐1,2,3,4‐tetrahydroisoquinoline‐1‐acetamides 5–8 react with formaldehyde or benzaldehyde to furnish stereoisomeric pyrimido[6,1‐a]isoquinolin‐2‐ones 9–18. The relative configurations and the predominant conformations of the products have been determined by NMR spectroscopy, and for (4S*,6R*,11bR*)‐9,10‐dimethoxy‐6‐methyl‐4‐phenyl‐1,3,4,6,7,11b‐hexahydropyrimido[6,1a]isoquinolin‐2‐one (11) by X‐ray diffraction.
Enantiopure Derivatives of 1,1,2‐Triphenylethane‐1,2‐diol by Unusual Ring Opening of Its Cyclic Sulfite
Authors: Fleischer Ralf , Galle Dietmar , Braun Manfred 
Published: July 2007

AbstractThe reaction of triphenylglycol (S)‐1with thionyl chloride leads to the cyclic sulfites2aand2bin a ratio of 90:10. When the mixture of diastereomers2a/bis treated with alcohols3or diols6, enantiomerically pure ethers5and7are obtained by an unexpected SN1‐type ring cleavage. Enantiopure triphenyloxirane (R)‐10arises under inversion of configuration upon treatment of2a/bwith sodium azide. The configuration of the major diastereomer2ais determined by NMR spectroscopy and by conversion into the sulfoxide (S)‐15.
Regulosides A–C: Glycosphingolipids from the Starfish Pentaceraster regulus
Authors: Venkannababu Uddagiri , Bhandari Shanker Pratap Singh , Garg Hari Shanker 
Published: July 2007

AbstractThe glycosphingolipid (GSL) composition of the starfish Pentaceraster regulus has been studied. The structure of the major component, a new cerebroside named Reguloside A (1) and two minor homologues, Regulosides B (1a) and C (1b), are described.
Evolution of the Concept of Synthesis Strategy in the COSYMA System: Introduction of the Synthesis Invariant
Authors: Ellermann Luc , Jauffret Philippe , Ostermann Claude , Kaufmann Gérard 
Published: July 2007

AbstractCOSYMA is a program for the computer‐assisted design of organic synthesis; its aim is to propose strategies for the synthesis of given compounds. These strategies are automatically learnt from global syntheses described in the literature, and adapted to the specifics of the target molecule. This paper describes an evolution of the formalization of synthesis strategy by taking into account untouched fragments, and the resulting improvement of the COSYMA program.
N,O Highly Regio‐ and Stereoselective Alkylation of Nucleophilic Glycine Equivalents with Carbonates of Allylic α‐Hydroxyphosphonates: A Convenient Route to Racemic 2‐Amino‐5‐phosphono‐4‐pentenoic Acids
Authors: Öhler Elisabeth , Kanzler Silvia 
Published: July 2007

AbstractPalladium(0)‐catalyzed allylic alkylation of diethyl (acetyl‐amino)malonate (6), ethyl (diphenylmethyleneamino)acetate (7), and (diphenylmethyleneamino)acetonitrile (8), respectively, with the acrolein‐derived 1‐dialkoxyphosphinyl‐substituted carbonates 5 provides the γ‐substituted vinylphosphonates 9–11 in very good yields and with high regioselectivity. The stereochemical outcome is dependent on the mode of nucleophilic activation of the glycine equivalents 6–8: When the reactions are performed in the presence of N,O‐bis(trimethylsilyl)acetamide (BSA) the (Z) isomers (Z)‐9–(Z)‐11 are highly favoured, while in the absence of any additional activation of the nucleophiles the corresponding (E) isomers predominate. In the latter case, upon alkylation of the Schiff base derivatives 7 and 8, up to 30% of the α‐substitution products 12 and 13, respectively, are isolated as by‐products. The vinylphosphonates 9–11 are easily converted to the racemic 2‐amino‐5‐phosphono‐4‐pentenoic acids (Z)‐3 and (E)‐3, and to the saturated analogue 1.