bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical Calculations of β‐Lactam Antibiotics. Part VI. AM1 calculations of alkaline hydrolysis of clavulanic acid
Authors: Frau Juan , Donoso Josefa , Muñoz Francisco , Blanco Francisco García 
Published: December 2004

AbstractThe gas‐phase basic hydrolysis of clavulanic acid (a) was studied by using the AM1 semi‐empirical method. The results obtained show that the hydroxyethylidene side chain at C(2) is pivotal to the stability of the different reaction products involved. The products with an open oxazolidine ring are more stable than those with a closed ring fused to the β‐lactam ring. This behaviour differs from that of penicillins and cephalosporins where the most stable degradation products are those with an intact thiazolidine or dihydrothiazine ring, respectively, fused to the β‐lactam ring. The different chemical reactivity of clavulanic acid relative to penicillins and cephalosporins could explain the disparate behaviour of the latter two types of compound towards β‐lactamases. Once the acyl‐enzyme intermediate of clavulanic acid has been formed, it can evolve with cleavage of the oxazolidine ring to form a difficult to deacylate compound.
Stereoselective Formation of Ternary Copper(II) Complexes of (S)‐amino‐acid amides and (R)‐ or (S)‐amino acids in aqueous solution
Authors: Dallavalle Francesco , Folesani Giuseppina , Marchelli Rosangela , Galaverna Gianni 
Published: December 2004

AbstractFormation constants of ternary complexes of CuII with (S)‐amino‐acid amides (phenylalaninamide, prolinamide, and tryptophanamide) and (R)‐ or (S)‐amino acids (valine, phenylalanine, proline, and tryptophan) were determined potentiometrically at 25° and I = 0.1M (KC1). Significant stereoselectivity was found for the systems (S)‐tryptophanamide/proline, (S)‐prolinamide/tryptophan, and (S)‐phenylalaninamide/proline, the diastereoisomeric complexes with ‘homochiral’ (SS) being more stable than with ‘heterochiral’ (SR) ligands. The stereoselectivity observed may be explained on the basis of repulsive interactions between the ligand side‐chain residues. The present data on the stability of mixed complexes in solution allow to draw some conclusions on the mechanism of chiral discrimination of amino acids in HPLC (reversed‐phase) using CuII complexes of (S)‐amino‐acid amides as selectors for ligand‐exchange chromatography (LEC).
Chemistry of the Higher Fullerenes: Preparative isolation of C76 by HPLC and synthesis, separation, and characterization of Diels‐Alder monoadducts of C70 and C76
Authors: Herrmann Andreas , Diederich François , Thilgen Carlo , Meer Hans‐Ulrich Ter , Müller Wolfgang H. 
Published: December 2004

AbstractHPLC Separation of higher fullerenes was compared on two different stationary phases, and the preparative isolation of pure C76 is described. Higher‐fullerene derivatives 1 and 2 were prepared by Diels‐Alder reaction of C70 and C76 with an ortho‐quinodimethane intermediate generated in situ. Three out of four possible isomeric C70 monoadducts, i.e. 1a–c, and, for the first time, one isomeric C76 monoadduct, i.e. 2c, could be isolated in pure form and characterized by 1H‐NMR, 13C‐NMR, UV/VIS, and mass spectrometry. Five other C76 isomers i.e., 2a,b,d–f were obtained in partially separated product fractions. Coalescence temperatures and energy barriers were determined for the cyclohexene‐ring inversion in two of the isomeric C70 derivatives. The structure of the C70 adducts could be deduced unambiguously from symmetry considerations based on high‐ and low‐temperature 1H‐NMR spectroscopy. A simple model for the qualitative evaluation of the local curvature of fullerene surfaces is presented and used for the prediction of addition sites in higher fullerenes. These predictions are compared to the experimental results mentioned above as well as to predictions resulting from π‐bond‐order considerations and from calculated pyramidalization angles.
The Reaction Mechanism of Chromanol‐Ring Formation Catalyzed by tocopherol cyclase from Anabaena variabilis KÜTZING (Cyanobacteria)
Authors: Stocker Achim , Derungs Giusep , Woggon Wolf‐Dietrich , Netscher Thomas , Rüttimann August , Müller Robert K. , Schneider Heinz , Todaro Louis J. 
Published: December 2004

AbstractIncubation of the synthetic 18O‐labelled phytyl‐hydroquinone (O4‐18O)‐2 with the tocopherol cyclase from Anabaena variabilis KÜTZING (Cyanobacteria) in D2O furnished the doubly labelled γ‐tocopherol, (2R,3S,4′R,8′R)‐(1‐18O,3‐2H)‐1. The chirality at C(3) was determined by two independent routes providing interlocking evidence that the enzyme‐catalyzed ring closure proceeds by si‐protonation of the double bond of 2 and concomitant re‐attack of the phenolic O‐atom.
Conformational Preferences and Absolute Configuration of Agelastatin A, a Cytotoxic Alkaloid of the Axinellid Sponge Agelas dendromorpha from the Coral Sea, via combined molecular modelling, NMR, and exciton splitting for diamide and hydroxyamide derivatives
Authors: Guerriero Antonio , D'Ambrosio Michele , Chiasera Giuseppe , Pietra Francesco 
Published: December 2004

AbstractThe absolute configuration of agelastatin A (1), the major, strongly cytotoxic alkaloid of the axinellid sponge Agelas dendromorpha from the Coral Sea, is proposed here to be (5aS,5bS,8aS,9aR), as deduced from combined molecular‐mechanics calculations and a novel application of exciton splitting to the bis[4‐(dimethylamino)benzoyl] compounds (–)‐9 and (–)‐13, derivatives of a diamide and a hydroxyamide, respectively. The position of the conformational equilibrium of A 1 could be finely tuned by slight molecular changes. The minor analogue, agelastatin B (3), was isolated as the trimethyl derivative (–)‐4.
Almazole C, a New Indole Alkaloid Bearing an Unusually 2,5‐Disubstituted Oxazole Moiety, and its putative biogenetic peptidic precursors, from a senegalese delesseriacean seaweed
Authors: Guella Graziano , Mancini Ines , Pietra Francesco 
Published: December 2004

AbstractFrom product isolation and biomimetic synthesis – which also establishes absolute configurations – the known oxazole alkaloids almazoles A ((+)‐1) and B ((+)‐2) seem to arise in a Senegalese delesseriacean seaweed from, in seuence, the new modified peptide prealmazole C ((+)‐4) and the oxazole alkaloid almazole C ((+)‐3a). N,N‐Dimethyl‐L‐phenylalaninamide ((+)‐7) and the new peptides (+)‐5 and (+)‐6, as well as a series of known small units, are also involved. In all cases, the oxazole ring is peculiarly 2,5‐inserted.
Monocarboxylates of 3‐Methylidene‐β‐lactams: Synthesis and unusual oxidative rearrangement into a spiro[azetidine‐3,3′‐pyrrolidine] derivative
Authors: Johner Michael , Rihs Grety , Gürtler Susanne , Otto Hans‐Hartwig 
Published: December 2004

AbstractReaction of the 3‐silylated β‐lactams 1 with glycoxalates gives bis‐lactam 3, but the same reaction in the presence of 1 equiv. of Me3SiCl leads to the formation of the disilylated adducts 5. The latter is desilylated by (Bu4N)F yielding the monocarboxylates 7 of 3‐methylidene‐β‐lactams, which, with oxidizing agents, give the spiro compound 8. The structure of 8 is established by spectroscopic data and a crystal‐structure analysis.
In vivo Investigation of Plant‐Cell Metabolism by means of natural‐abundance 13C‐NMR spectroscopy
Authors: Lutterbach Ralf , Stöckigt Joachim 
Published: December 2004

AbstractBased on the natural abundance of 13C, in vivo 13C‐NMR was used for the first time to monitor the metabolism of sucrose and hydroquinone (1) in cell suspensions of the plant Rauwolfia serpentina (L.) BENTH. ex KURZ. Cells converted sucrose extracellularly into α‐D‐ and β ‐D‐glucose as well as into β ‐D‐fructofuranose and β ‐D‐fructopyranose, respectively. The sugar mixture was completely taken up by the cells after 4 days. Hydroquinone fed at that time resulted in optimum conversion into its β ‐D‐glucoside arbutin (2) within 10 h. A further metabolite, the primeveroside (3) of hydroquinone, appeared as a trace compound after 10 h. The formation of this diglycoside can be increased by further addition of sucrose.
Temporary Protection and Activation in the Regioselective Synthesis of Saccharide Sulfates
Authors: Langston Steven , Bernet Bruno , Vasella Andrea 
Published: December 2004

AbstractRegioselective sulfation with Et3N · SO3 of partially protected or unprotected glycosides via stannanediyl acetals or stannyl ethers, combined with persistent or temporary protecting groups is described. Stannylation of phenylboronates, followed by sulfation and aqueous workup, is an efficient way for the synthesis of monosulfated monosaccharides. The stannanediyl acetal 2 led in high yields to 3a, while sulfation of the diol 1 proceeded more slowly and led in lower yield to a mixture 1/3a/4a/5a (Scheme 1). The trehalose disulfate 8a was obtained in high yields from 7; reducing the amount of sulfating agent led to a mixture 6/8a/9a. Stannylation and sulfation of the galactoside 11 afforded 13a, while direct sulfation of 11 gave a mixture of the 2‐and 3‐sulfates 13a/14a besides some disulfate 15a. Sulfation of the lactose derivative 16 and the stannanediyl acetal 17 gave the 3‐sulfate 18a, with some disulfate 19a being formed from 16. The mannopyranoside 21 was selectively sulfated at OH–C(2), leading to 22a, while the corresponding diol 20 yielded mostly the isomer 23a and some disulfate 24a. Sulfation of the stannyl ethers derived from the gluco‐and galactopyranosides 25 and 28 and (Bu3Sn)2O afforded high yields of the 2,6‐disulfate 26a and the 3,6‐disulfate 29a, respectively. Stannylation of 25 and 28 with Bu2SnO and sulfation proceeded less satisfactorily. Stannylation of the phenylboronate 32 (Bu2SnO) and sulfation gave good yields of the 2‐sulfate 27a; stannylation and benzoylation yielded the 2‐benzoate 34 (Scheme 2). Similarly, the galactose‐derived 37 provided high yields of the 3‐sulfate 30a and of the 3‐benzoate 39. Direct sulfation of the phenylboronates 32 and 37 proceeded in lower yields and gave mixtures.
Interaction of Double‐Helical Polynuclear Copper(I) complexes with double‐stranded DNA
Authors: Schoentjes Bruno , Lehn Jean‐Marie 
Published: December 2004

AbstractDouble‐helical metal complexes, the helicates H2–H5, were found to bind to double‐helical DNA by spectroscopic, DNA‐melting, and electrophoretic‐mobility measurements. The helicates also inhibited the cleavage of DNA by two restriction enzymes, Sspl and EcoRV, a property which agrees with the binding occurring in the major groove of the double helix. Visible‐light irradiation of solutions containing a helicate and the pBR322 plasmid led to single‐strand cleavage, indicating that these complexes could be of interest as potential probes for nucleic‐acid structure.
Chelate‐Controlled Asymmetric Synthesis of 2‐Substituted 2,3‐Dihydropyridin‐4(1H)‐ones: Synthesis of D‐ and L‐aminodeoxyaltrose derivatives
Authors: Streith Jacques , Boiron Arnaud , Paillaud Jean‐Louis , Rodriguez‐Perez Elsa‐Maria , Strehler Christiane , Tschamber Théophile , Zehnder Margareta 
Published: December 2004

AbstractAsymmetric methylation and phenylation of the chiral pyridinium salt 7, as well as methylation of chiral pyridinium salt 18, with Grignard reagents occurred in good yield and with good‐to‐excellent diastereoselectivities (Schemes 2 and 3, resp.). These results are best explained by assuming chelate control to govern the asymmetric alkylation/arylation process. The minimum‐energy conformations of the out‐of‐plane twisted pyridinium salts 7 and 18, as determined by the ‘Molecular Simulations Cerius‐Dreiding II’ program, are in good agreement with the postulated asymmetric chelate‐control mechanism.
Neuartige Alkaloide aus dem Giftdrüsensekret sozialparasitischer Ameisen (Myrmicinae: Leptothoracini)
Authors: Reder Elke , Veith Hans Jürgen , Buschinger Alfred 
Published: December 2004

Novel Alkaloids from the Poison Glands of Ants LeptothoraciniNovel pyrrolidine alkaloids were isolated from the poison glands of ants Leptothoracini(Myrmicinae) and identified as a mixture of N‐alkylated 3‐methylpyrrolidines. The females of these species produce male‐attracting pheromones in their poison glands. The basic compounds in the secretions were found to be active. The major alkaloid, 3‐methyl‐1‐(3‐methylbutyl)pyrrolidine (5), is present in only ng quantities per gland.
Angular Alkylation of cis‐Decalin Epoxides with C‐nucleophiles: Mechanism, scope, and limitations of a novel bridgehead functionalisation
Authors: Huber Udo , Boland Wilhelm 
Published: December 2004

AbstractThe angular alkylation of cis‐decalin epoxides like 5 or 7 can be achieved at C(8a)For convenience, the arbitrary numbering given for 5 (Scheme I) is used throughout the General Part; for systematic names, see Exper. Part.
in good yield by using CuI and a large excess of Grignard reagents without an sp3 centre at C(2). The reaction proceeds via a carbenium‐ion intermediate which is stabilised by homoconjugative interaction with the adjacent double bond. Due to 1,3‐diaxial strain in the alkoxides resulting from alkylation or reduction at C(4a) of the epoxides 5 or 7, the nucleophile is delivered selectively to C(8a). Grignard reagents possessing H‐atoms at C(β), transfer a hydride to the epoxide yielding the trans‐decalol 11 (Grignard reduction). The angular alkylation of 5 with allylic and benzylic Grignard reagents proceeds with good yield.
Complete π‐Facial Stereoselectivity in the TiCl4‐Mediated [4 + 2] Cycloaddition of Cyclopentadiene to N,N′‐fumaroyldi[(2R)‐bornane‐10,2‐sultam]
Authors: Chapius Christian , Rzepecki Piotr , Bauer Tomasz , Jurczak Janusz 
Published: December 2004

AbstractUnder the co‐operative influence of two prosthetic groups, and independent of the TiCl4 concentration, complete and constant diastereofacial π‐selection was achieved during the [4 + 2] cycloaddition of cyclopentadiene to N,N′‐fumaroyl‐di[(2R)‐bornane‐10,2‐sultam] ((−)‐1c); reactive conformations are discussed.
NMR‐Spectroscopic Investigations of Potentially Planarized Nonafulvenes
Authors: Chai Shengyong , Bönzli Peter , Neuenschwander Markus 
Published: December 2004

Abstract1H‐ and 13C‐NMR spectra of nonafulvene 1e and nonafulvenes 2 and 3 have been assigned, high‐resolution 1H‐NMR spectra of 2 (600 MHz, Fig. 3) and of 3 (400 MHz, Fig. 2) have been analyzed, and the data are compared with those of other nonafulvenes (Tables 1–6). Generally speaking, according to their spectroscopic behavior, four classes of nonafulvenes (A–D) may be distinguished (Fig. 1). The investigation shows that compounds 1e and 3 belong to class A, being characterized by 1H‐chemical shifts around 6 ppm, strongly alternating 3J(H,H) and 13C chemical shifts in the range of 123 to 130 ppm, thus existing in the olefinic form with a non‐planar nine‐membered ring. On the other hand, 2 is the first nonafulvene of class D, being characterized by 1H chemical shifts in the aromatic range, large 3J(H,H) values of the same size, and 13C chemical shifts around 110 ppm. Since NMR parameters are virtually not influenced by temperature (−50° to 50°) or solvents, it is concluded that 2 exclusively exists in the dipolar structure 2± with a planarized nine‐membered ring. According to Fig. 4, these classes (and their spectroscopic data) are linked by 10,10‐bis(dimethylamino)nonafulvene (1c; and its temperature‐dependent NMR parameters): for 1c, a temperature‐dependent equilibrium 1c⇌1c± had earlier been established.
Synthesis of 4,6,8‐Trisubstituted Methyl Azulene‐2‐carboxylates
Authors: Rippert Andreas Johannes , Hansen Hans‐Jürgen 
Published: December 2004

AbstractIt is shown that sodium (methoxycarbonyl)cyclopentadienide (1), which is easily accessible from sodium cyclopentadienide and dimethyl carbonate in THF, reacts with 2,4,6‐trisubstituted pyrylium tetrafluoroborates 2a–d in boiling MeOH to afford the corresponding methyl azulene‐2‐carboxylates 4a–d in good yields. The corresponding 1‐carboxylates 3 were not found (cf. Schemes 1 and 2).
Biosynthetic Production of [N2,1,3,7,9‐15N]Guanosine and [1,3,7,9‐15N]inosine and conversion into [N6,1,3,7,9‐15N]adenosine for structure elucidation of RNA by heteronuclear NMR
Authors: Niemann Annette C. , Meyer Mónica , Engeloch Thomas , Botta Oliver , Hädener Alfons , Strazewski Peter 
Published: December 2004

AbstractA procedure was developed for the biosynthetic preparation of 15N‐labelled guanosine and inosine through the action of a mutant Bacillus subtilis strain. Crude [N2,1,3,7,9‐15N]guanosine and [1,3,7,9‐15N]inosine were isolated from the culture filtrate by precipitation and anion‐exchange chromatography (Scheme 1). No cell lysis and no enzymatic degradation was necessary. The per‐isobutyrylated derivatives 1 and 2 were isolated from a complex mixture, purified by virtue of their different lipophilicity, and separated in three steps involving normal‐and reversed‐phase silica‐gel chromatography. One litre of complex nutrient medium yielded 8.44 mmol of guanosine derivative and 2.84 mmol of inosine derivative with high average 15N enrichment (83.5 and 91.9 atom‐%, resp.). [N6,1,3,7,9‐15N]Adenosine (4) was obtained from 2′,3′,5′‐tri‐O‐isobutyryl[1,3,7,9‐15N]inosine (1) through the ammonolysis of its 1,2,4‐triazolyl derivative with aqueous 15NH3 (Scheme 2).
Lipophilic Functionalized Cobyrinic‐Acid Derivatives. Part 1. Cobester α‐monoacids (α,α,α,β,β,β‐hexamethyl α‐hydrogen Coα, Coβ‐dicyanocobyrinates)
Authors: Kräutler Bernhard , Caderas Christian , Konrat Robert , Puchberger Michael , Kratky Christoph 
Published: December 2004

AbstractThe four α,α,α, β,β,β,‐hexamethyl α‐hydrogen Coα, Coβ‐dicyanocobyrinates 2b, d–f, with a free b‐, d‐, e‐, and f‐propionic‐acid function, respectively, were prepared by partial hydrolysis of heptamethyl Coα, Coβ‐dicyanocobyrinate (cobester; 1) in aqueous sulfuric acid. The cobester monoacids 2b, d–f were obtained as a ca. 1:1:1:1 mixture which was separated. The monoacids were purified by chromatography and isolated in crystalline form. The position of the free propionic‐acid function was determined by an extensive analysis of 2b, d–f using 2D‐NMR techniques; an analysis of the C,H‐coupling network topology resulted in an alternative assignment strategy for cobyrinic‐acid derivatives, based on pattern recognition. Additional information on the structure of the most polar of the four hexamethyl cobyrinates, of the b‐isomer 2b, was also obtained in the solid state from a single‐crystal X‐ray analysis. Earlier structural assignments based on 1D‐NMR spectra of the corresponding regioisomeric monoamides 3b, d–f (obtained from crystalline samples of the monoacids 2b, d–f) were confirmed by the present investigations.
Synthesis, Characterization, and Electrochemical and Photophysical Properties of Rhenium(I) and ruthenium(II) complexes of 2,2′‐bipyridine ligand functionalized β‐cyclodextrins
Authors: Deschenaux Robert , Ruch Thomas , Deschenaux Pierre‐François , Juris Alberto , Ziessel Raymond 
Published: December 2004

AbstractThe synthesis, characterization, and electrochemical and photophysical properties of the ReI and RuII complexes of permethylated β‐cyclodextrins, functionalized on the primary face by a 2,2′‐bipyridine ligand, are reported. For comparison, model compounds, in which the cyclodextrin was replaced by a Me group, were also prepared and their properties investigated.
Determination of the Absolute Configuration of a Series of Halogenated Furanones from the marine alga delisea pulchra
Authors: König Gabriele M. , Wright Anthony D. , Bernardinelli Gérald 
Published: December 2004

AbstractThe absolute configuration of a series of naturally occurring and semi‐synthetic halogenated furanones is proposed on the basis of chemical interconversions and X‐ray and CD analyses. The CD analyses clearly reveal that the presence of the allylic O‐atom has a strong influence in determining the sign and intensity of the low energy π→π* transition.
An Efficient Straightforward Synthesis of Benz[a]azulene
Authors: Sperandio David , Hansen Hans‐Jürgen 
Published: December 2004

AbstractBenz[a]azulene (1) is synthesized in five steps (cf. Scheme 2) starting from commercially available 2‐iodobenzyl alcohol (4) and tropylium tetrafluoroborate in an overall yield of 44%. The key step (cf. also Scheme 1) is the intramolecular Heck reaction of the 8‐phenylsulfonyl‐substituted heptafulvene 7, which leads in nearly quantitative yield directly to 10‐(phenylsulfonyl)benz[a]azulene (8). The desulfonylation of 8 can be accomplished by Julia's method with Na2S2O4/NaHCO3 in DMF/H2O at 85–90°, thus leading to pure 1 in 78% yield. The phenylation of 8 with PhLi or PhCul at −78° in THF occurs regioselectively at C(9). Dehydrogenation of the formed dihydroazulenes with o‐chloroanil in toluene at room temperature gives 9‐phenyl‐10‐(phenylsulfonyl)‐benz[a]azulene (9) in 70% yield (cf. Scheme 3), which, again, can be desulfonylated with Na2S2O4/NaHCO3 in DMF/H2O in good yields. The addition of PhLi to 1 in THF occurs at temperatures ⩾ −25°. Ionic dehydrogenation (1. Ph3C+BF/MeCN; 2. Et3N) of the dihydro forms leads to 3, as the main product, and its positional isomers.
Synthesis of Spiro[cyclohexane‐1,2′‐[2H]indene] derivatives as inhibitors of steroid 5α‐reductase
Authors: Lin Shu‐Kun , Rasetti Vittorio 
Published: December 2004

AbstractThe spiro[cyclohexane‐1,2′‐[2H]indene] derivatives 15a,b with molecular dimensions and nucleophilic functional groups similar to known steroid 5α‐reductase inhibitors (e.g. 2) were synthesized. The spiro[cyclohexane‐1,2′‐[2H]indene]‐1′(3′H),4‐dione (5) was synthesized from 5‐methoxyindan‐l‐one ( = 2,3‐dihydro‐5‐methoxy‐1H‐inden‐1‐one). A Grignard reaction and a dehydration step led to the cyclohexene (±)‐7 which, upon a stereoselective hydrogenation catalyzed by Raney‐Ni under mild conditions, gave 8a as a pure epimer. Further hydrogenation and hydrogenolysis of 8a over Pd/C at room temperature reduced the keto group to give pure 9a. Finally, the 5′‐substituted derivatives 12a, 14a, and 15a were generated by deprotection and Heck‐type reaction.
Functionalized Nitroalkanes in Organic Synthesis. The first concise preparation of 4‐hydroxyheptadecan‐7‐one and 14‐hydroxyoctadecan‐8‐one, two new hydroxy ketones isolated from Chiococca alba
Authors: Ballini Roberto , Bosica Giovanna , Rafaiani Gianni 
Published: December 2004

AbstractThe 4‐hydroxyheptadecan‐7‐one (1) and 14‐hydroxyoctadecan‐8‐one (2), two new hydroxyketones isolated from leaves of Chiococca alba, were synthesized, for the first time, by hydroxy‐functionalized nitroalkanes 4 and 9, respectively, via two chemoselective key steps: i) nitroaldol condensation with basic alumina, and ii) direct Nef conversion of nitroalkenes to carbonyl derivatives with sodium hypophosphite, in order to preserve the OH group.
Enantioselective Alternating Olefin‐Carbon Monoxide Copolymerization: A new concept for activity and stereoselectivity
Authors: Bronco Simona , Consiglio Giambattista , Di Benedetto Silvia , Fehr Matthias , Spindler Felix , Togni Antonio 
Published: December 2004

AbstractCationic Pd‐complexes modified by dicyclohexyl{(R)‐1‐[(S)‐2‐(diphenylphosphino)ferrocenyl]ethyl}phosphine (1a) give very active catalytic systems for the regioregular isotactic specific copolymerization of propene with CO. Other alk‐1‐enes also give stereoregular and regioregular copolymers, even if with lower productivity. The copolymers are isolated as poly(4‐alkyl‐tetrahydrofuran‐2,2,5,5‐tetrayl‐2‐oxy‐2‐methylenes) B in the solid state and give the isomeric poly(2‐alkyl‐1‐oxopropane‐1,3‐diyls) A by dissolution in (CF3)2CHOH. Solid polymer A (R = Et) is formed back at least partially when the dissolved material is reprecipitated from MeOH. The use of the related (ferrocenyl)diphosphine ligands 1b−e and 2 as the catalyst modifier shows that the presence of both elements of chirality and of large substituents on the P‐atoms of the ligand is necessary to achieve good stereocontrol, and that the large difference in basicity between the two P‐atoms is probably the reason for the good catalytic activity.