bluuebunny/crossref_metadata_2025_split huggingface dataset:
Silica‐Gel‐Confined Ionic Liquids: A New Attempt for the Development of Supported Nanoliquid Catalysis
Authors: Shi Feng , Zhang Qinghua , Li Dongmei , Deng Youquan 
Published: July 2005

AbstractA new concept of designing and synthesizing highly dispersed ionic‐liquid catalysts was developed through physical confinement or encapsulation of ionic liquids (with or without metal complex) in a silica‐gel matrix through a sol–gel process. We studied ionic liquids such as EMImBF4, BuMImBF4, DMImBF4, CMImBF4, BuMImPF6, either with or without [Pd(PPh3)2Cl2] and [Rh(PPh3)3Cl], in a silica‐gel matrix (E=ethyl, Bu=butyl M=methyl, D=decyl, C=cetyl and Im=imidazolium). The contents of ionic liquids and loadings of Pd or Rh were 8–53 wt % and 0.1∼0.15 wt %, respectively. Analyses of FT‐Raman spectra showed that abnormal Raman spectra of the confined ionic liquids were observed in comparison with the bulk and pure ionic liquids. EMImBF4 and BuMImBF4 ionic liquids could be completely washed out from the silica‐gel matrix under vigorous reflux conditions, but ionic liquids with larger molecular size, for example, DMImBF4 or CMImBF4, could be confined into the silica‐gel nanopores relatively firmly. These results suggested that the ionic liquids were physically confined or encapsulated into the silica gel. The N2 adsorption measurements indicated that the silica‐gel skeleton was mesoporous with 50–110 Å pore size after the BuMImBF4 ionic liquid was removed completely. Transmission electron microscopy (TEM) and X‐ray diffraction (XRD) analysis showed that the silica‐gel matrix was amorphous and non‐uniformly mesoporous. Carbonylation of aniline and nitrobenzene for synthesis of diphenyl urea, carbonylation of aniline for synthesis of carbamates, and oxime transformation between cyclohexanone oxime and acetone were used as test reactions for these catalysts. Catalytic activities were remarkably enhanced with much lower amounts of ionic liquids needed with respect to bulk ionic‐liquid catalysts or silica‐supported ionic‐liquid catalysts prepared with simple impregnation, in which the ionic liquid may be deposited as a thin layer on the support. Such unusual enhancement in catalytic activities may be attributed to the formation of nanoscale and high‐concentration ionic liquids due to the confinement of the ionic liquid in silica gel; this results in unusual changes in the symmetry and coordination geometry of the ionic liquids.
Rotamer Stability incis‐[Pt(diA)G2] Complexes (diA=Diamine Derivative and G=Guanine Derivative) Mediated by Carrier‐Ligand Amine Stereochemistry as Revealed by Circular Dichroism Spectroscopy
Authors: Benedetti Michele , Marzilli Luigi G. , Natile Giovanni 
Published: July 2005

AbstractExtensive investigations ofcis‐[Pt(diA)G2] complexes (in which G=a guanine ligand; diA=a single diamine ligand) revealed the types of interactions between the two G ligands and between the G and thecis‐amine substituents when diA is a diamine ligand with substituents on each nitrogen atom being a small hydrogen atom and a bulky group able to slow the rotation about the PtG bond. All these interactions are shown to apply also when diA=dach (1,2‐diaminocyclohexane), even though this chiral primary diamine has only small NH atoms on each side of the coordination plane. However, a slight difference in the stereochemistry of the two protons (one NH has “quasi axial” and the other “quasi equatorial” character) is sufficient to induce a significant change in the relative stabilities of the [Pt(dach)G2]ΔHT andΛHT rotamers (HT=head‐to‐tail). The new results show that at acidic and neutral pH the induction of asymmetry from the dach ligand to the HT rotamers is governed by the G‐to‐G dipole–dipole interaction, which is greater for the six‐membered ring of each guanine leaning towards thecis‐G. Such a “six‐in” canting of the two guanine ligands can be hampered by the steric interaction between the H8 of each guanine and the substituent on thecis‐amine that is on the same side of the coordination plane. Such a repulsion is greater for a “quasi equatorial” NH than for a “quasi axial” NH. Under basic pH conditions, deprotonation of the guanine N1H renders the O6 atom a much better hydrogen‐bond acceptor; therefore, the stability of the HT rotamers is governed by the hydrogen‐bond interaction of guanine O6 and thecis‐amine NH group. Such a guanine O6/NHcis‐amine interaction is stronger for a “quasi axial” than for a “quasi equatorial” NH group. In the head‐to‐head (HH) rotamer, in which the electrostatic repulsion between electron‐rich O6 atoms, both on the same side of the platinum coordination plane, tends to place the six‐membered rings of each guanine further from thecis‐guanine and closer to thecis‐amine, we can expect better NH⋅⋅⋅O6 hydrogen bonding for the “quasi equatorial” NH groups.
Study on the Binding of Base‐Mismatched Oligonucleotide d(GCGAGC)2 by Cobalt(III) Complexes
Authors: Chen Huili , Yang Pin , Yuan Caixia , Pu Xiaohua 
Published: July 2005

AbstractThe binding of [Co(phen)2(HPIP)]Cl3 and [Co(phen)2(DPQ)]Cl3 to the oligonucleotide d(GCGAGC)2 containing two sheared G:A mispairs has been studied by NMR spectroscopy for the first time. For both the complexes, a considerable number of intermolecular NOEs were observed in NOESY spectra of the cobalt‐complex‐bound hexanucleotide. The results suggest that [Co(phen)2(HPIP)]Cl3, with HPIP, intercalates between the G3:A4 base pairs from the minor groove and extends to the major groove, and [Co(phen)2 (DPQ)]3+ binds to the terminal G5:C6 region from two directions. 31P NMR spectroscopy indicates that [Co(phen)2(HPIP)]Cl3 binding induces a change in the phosphate backbone in the region of the mismatched base pairs, while [Co(phen)2 (DPQ)]3+ does not cause obvious changes in the backbone. Melting experiments indicate that [Co(phen)2(HPIP)]Cl3 stabilizes the double‐strand structure, while [Co(phen)2(DPQ)]Cl3 cause the duplex to untwist. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Adsorption of Zn2+ and Cd2+ from Aqueous Solution onto a Carbon Sorbent Containing a Pyrimidine–Polyamine Conjugate as Ion Receptor
Authors: García‐Martín Javier , López‐Garzón Rafael , Godino‐Salido Mari Luz , Cuesta‐Martos Rafael , Gutiérrez‐Valero Maria Dolores , Arranz‐Mascarós Paloma , Stoeckli‐Evans Helen 
Published: July 2005

AbstractThe compound N‐(4‐amino‐1‐methyl‐5‐nitroso‐6‐oxo‐1,6‐di‐hydropyrimidin‐2‐yl)‐N'‐[bis(2‐aminoethyl)]ethylenedi‐amine (HL) was synthesised and structurally characterised by analytical methods and 1H, 13C and 15N NMR spectroscopy. The protonation of HL and its coordinating ability towards Zn2+ and Cd2+ ions in water solution were also studied by potentiometric methods and UV/Visible and 1H‐13C NMR spectroscopy. The molecular structures of [H3L]2+[CdI4]2–·2H2O and [(Cl3Zn)(μ‐Cl){Zn(μ2‐HL)}]2·2.5H2O were solved by single‐crystal X‐ray diffraction methods. On the basis of these data, the performance of HL anchored to activated carbon (AC) was evaluated as a molecular receptor for Zn2+ and Cd2+ metal ions in aqueous solution. This was done by a comparative study of the adsorption capacity of the adsorbents AC alone and HL anchored on the AC (AC‐HL) for these metal ions and by a structural study of the AC‐HL, AC‐HL‐Zn2+ and AC‐HL‐Cd2+ solid phases by XPS and IR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Influence of 2‐Aminopyridine on the Formation of Molybdates under Hydrothermal Conditions
Authors: Pavani Katikaneani , Ramanan Arunachalam 
Published: July 2005

AbstractThe hydrothermal reaction of an aqueous ammonium heptamolybdate solution with first‐row transition metal salts in the presence of 2‐aminopyridine at around 180 °C and under autogenous pressure yields several molybdates, such as the 1D chains in (C5N2H7)4Mo8O26 (1), zero‐dimensional (C5N2H7)6Mo7O24·3H2O (2), and the first synthesis of Lindgrenite [Cu3Mo2O8(OH)2 (3)] The structures of these materials were established by single‐crystal and powder X‐ray diffraction techniques. The crystal structures of wolframite‐based MnMoO4 (4) and ZnMoO4 (5) were established by powder X‐ray diffraction. The role of 2‐aminopyridine (2‐ampy) in the formation of the different solids under hydrothermal conditions is discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Identification of Copper(II) Binding Sites in the Aminoglycosidic Antibiotic Neomycin B
Authors: Jeżowska‐Bojczuk Małgorzata , Szczepanik Wojciech , Mangani Stefano , Gaggelli Elena , Gaggelli Nicola , Valensin Gianni 
Published: July 2005

AbstractProtonation and copper(II) coordination properties of neomycin B were studied in solution by potentiometry, NMR, UV/Vis, CD, and EPR spectroscopy, XAS and mass spectrometry. Mono‐ and dinuclear complexes were found depending on the metal‐to‐ligand molar ratio. Neomycin B anchors CuIIions above pH 5.0 with an NH2group from ring B. Simultaneously, the second amino group of the same ring and the hydroxyl group of ring A complete the binding set of donors. With an increase in pH the remaining –NH3+functional groups in the neomycin B molecule are deprotonated without affecting the complexation pattern. However, these groups, particularly the ones located in theD‐ring of the antibiotic, may coordinate the second copper(II) ion when the metal is present in excess. We have proved this process with the use of potentiometry, CD and especially mass spectrometry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Copper, Cobalt and Platinum Complexes with Dithiothiophene‐Based Ligands
Authors: Belo Dulce , Figueira Mauro J. , Mendonça Joana , Santos Isabel C. , Almeida Manuel , Henriques Rui T. , Duarte Maria Teresa , Rovira Concepció , Veciana Jaume 
Published: July 2005

AbstractThe preparation and characterisation of new thiophenedithiolate complexes of Cu, Co and Pt with the ligands α‐tpdt and tpdt (α‐tpdt = 2,3‐thiophenedithiolate, tpdt = 3,4‐thiophenedithiolate) is reported. The Co and Pt complexes present regular square‐planar coordination geometry and low oxidation potentials when compared with complexes with simpler ligands, but their monoanionic state is found to be rather unstable. The Co(tpdt)2 complex can be isolated both in the monoanionic and dianionic states as a stable compound but the Co(α‐tpdt)2 and the Pt complexes can be obtained only in the dianionic state, while their monoanionic state is unstable. The Co and Pt complexes can, however, be easily oxidised to the neutral state, giving a fine‐powdered microcrystalline material without high electrical conductivity. With Cu only a less frequent geometry based on a tetrametallic CuI cluster and three ligands is observed as [Cu4(α‐tpdt)3]2– and [Cu4(tpdt)3]2–. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
The Reductive Elimination of Methane from ansa‐Hydrido(methyl)metallocenes of Molybdenum and Tungsten: Application of Hammond’s Postulate to Two‐State Reactions
Authors: Carreón‐Macedo José‐Luis , Harvey Jeremy N. , Poli Rinaldo 
Published: July 2005

AbstractThe energetic profile of the methane reductive elimination from a selected number of hydrido(methyl)molybdenocene and ‐tungstenocene derivatives has been calculated by DFT methods. The calculations were carried out for the CH2(C5H4)2M (a‐M), SiH2(C5H4)2M (a‐H2Si–M), and SiMe2(C5Me4)2M (a‐Me2Si–M*) ansa‐metallocene systems for M = Mo, W. They include the full optimization of minima [the hydrido(methyl) starting complexes, M(H)(CH3), the intermediate methane complexes, M(CH4), and the metallocene products in the singlet and triplet configurations, (3M and 1M)], transition states (for the methyl hydride reductive elimination, M–TSins, and for the hydrogen exchange, M–TSexch), and the minimum energy crossing point (M–MECP) leading from the singlet methane complexes to the corresponding triplet metallocenes. The results are compared with those previously obtained for the simpler (C5H5)2M (Cp2M) systems (J. C. Green, J. N. Harvey, and R. Poli, J. Chem. Soc., Dalton Trans. 2002, 1861). The calculated energy profiles, notably the relative energies of M–TSins and M–MECP, are in agreement with available experimental observations for the a‐Me2Si–M* systems. The comparison of the energies and geometries of the rate‐determining M–TSins and M–MECP structures with those of the thermodynamically relevant minima for the various systems show the applicability of Hammond’s postulate to two‐state reactions. However, one notable exception serves to show that the principle is only quantitatively reliable when all the potential energy surfaces for the set of analogous reactions have similar shapes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Synthesis and Reactivity of 1,2‐ and 1,3‐Diphosphanes that Contain Four Chiral Rhenium Fragments: Architecturally Novel Tetrametallo‐DMPE and ‐DMPP Species that are Unprivileged Ligands for Enantioselective Catalysis
Authors: Kromm Klemenz , Eichenseher Sandra , Prommesberger Markus , Hampel Frank , Gladysz J. A. 
Published: July 2005

AbstractReactions of enantiopure (S)‐[(η5‐C5H5)Re(NO)(PPh3)(=CH2)]+ PF6– [(S)‐2] and PH2CH2(CH2)nCH2PH2 (0.5 equiv.) give (SReSRe)‐[(η5‐C5H5)Re(NO)(PPh3){CH2PH2CH2(CH2)nCH2PH2CH2}(Ph3P)(ON)Re(η5‐C5H5)]2+ 2PF6– [n = 0/1, (SReSRe)‐3/4; 65–62/77–58 %]. Reaction of racemic 2 (BF4– salt) and PH2(CH2)2PH2 (0.5 equiv.) gives the meso and rac diastereomers of 3 (BF4– salts) in 28 % and 38 % yields after crystallization. Treatments of (SReSRe)‐3/4 with tBuOK and then (S)‐2 give the tetrarhenium complexes (SReSReSReSRe)[{(η5‐C5H5)Re(NO)(PPh3)(CH2)}2{PHCH2(CH2)nCH2PH}{(CH2)(Ph3P)(ON)Re(η5‐C5H5)}2]2+ 2PF6– [n = 0/1, (SReSReSReSRe)‐7/8; 89–88/98–87 %]. The crystal structure of(SReSReSReSRe)‐7 is determined and its conformation analyzed. Reactions of (SReSReSReSRe)‐7/8 and tBuOK give air‐sensitive diphosphanes (SReSReSReSRe)‐{(η5‐C5H5)Re(NO)(PPh3)(CH2)}2{PCH2(CH2)nCH2P}{(CH2)(Ph3P)(ON)Re(η5‐C5H5)}2 [n = 0/1, (SReSReSReSRe)‐9/10; 92/62 %]. Additions of (a) PhIO give the corresponding dioxides (72/62 %), and (b) [Rh(NBD)2]+ PF6– give the corresponding chelates [(P–P)Rh(NBD)]+ PF6– (75/82 %) (NBD = norbornadiene). These catalyze hydrogenations of protected dehydroamino acids and hydrosilylations of propiophenone with only modest enantioselectivities. Similar results are obtained when (SReSReSReSRe)‐9/10 are applied in rhodium‐catalyzed conjugate additions of aryl boronic acids, or palladium‐catalyzed allylic alkylations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Synthetic and Theoretical Aspects of New Dimroth Rearrangement of6‐Aminopyran‐2‐ones to 6‐Hydroxypyridin‐2‐ones via Carbamoyl Ketenes
Authors: Subbotina Julia O. , Fabian Walter M. F. , Tarasov Evgeniy V. , Volkova Natalia N. , Bakulev Vasiliy A. 
Published: July 2005

AbstractTwo alternative directions for thermal transformation of 6‐amino‐4‐oxopyrano[3,4‐d] [1,2,3]thiadiazoles1, leading either to 6‐hydroxy‐4‐oxo‐[1,2,3]thiadiazolo[4,5‐c]pyridines2or 2‐cyano‐2‐(1,2,3‐thiadiazol‐5‐yl)acetamide4b, were observed. The first one represents a new, Dimroth‐type rearrangement and proceeds by thermal opening of the pyrane ring, followed by the simultaneous rotational isomerization of the ketene intermediate7(s‐cis) to7(s‐trans) and its recyclization onto the amido group to form the pyridin‐2‐one cycle.The first step of the rearrangement has a calculated [B3LYP/6‐31G(d)] activation barrier of 24–34 kcal/mol, the involvement of amines reduces it by ca. 5 kcal/mol [PCM‐B3LYP/6‐31G(d), DMSO]. In contrast, the recyclization step onto the amido group is calculated to occur essentially barrierless (ΔE< 2 kcal/mol). The influence of substituents, in particular of those capable of intramolecular hydrogen bonding, on the preferred reaction path was also studied. The alternative ring opening of the pyrane cycle was calculated to be at least 5 kcal/mol [B3LYP/6‐31G(d)] less favorable than the Dimroth rearrangement. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
The P‐Stereocontrolled Synthesis of PO/PS‐Chimeric Oligonucleotides by Incorporation of Dinucleoside Phosphorothioates Bearing an O‐4‐Nitrophenyl Phosphorothioate Protecting Group
Authors: Wozniak Lucyna A. , Góra Marcin , Bukowiecka‐Matusiak Małgorzata , Mourgues Sophie , Pratviel Geneviève , Meunier Bernard , Stec Wojciech J. 
Published: July 2005

AbstractThe synthesis of protected model dinucleoside (3',5')‐O‐aryl phosphorothioates, their separation into pure diastereomers, and their successful incorporation into oligonucleotides followed by stereospecific deprotection of the O‐aryl phosphorothioate function with oximate ion (inversion) enables the preparation of chimeric PO/PS‐oligonucleotides with a predetermined sense of P‐chirality at each internucleotide phosphorothioate position. The absolute configuration at the phosphorus of the internucleotide O‐aryl phosphorothioate in “dimeric building blocks” has been assigned. The 3'‐terminal SP‐phosphorothioate linkages effectively protect such chimeric constructs from degradation by human plasma exonuclease (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Flexible Stereo‐ and Regioselective Synthesis of myo‐Inositol Phosphates(Part 2): Via Nonsymmetrical Conduritol B Derivatives
Authors: Podeschwa Michael A. L. , Plettenburg Oliver , Altenbach Hans‐Josef 
Published: July 2005

AbstractA practical route is described for the preparation of myo‐inositol phosphates. Optically pure compounds can be prepared, in both forms, from p‐benzoquinone by enzymatic resolution of a diacetoxyconduritol key intermediate. Monosubstituted inositol derivatives can be obtained by breaking the C2 symmetry of conduritol B derivatives. A wide variety of myo‐inositol phosphates can be synthesized by combining the previously reported symmetrical approach with this new nonsymmetrical approach. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
A Soluble and Reusable Colorimetric Sensor Based on the Covalent Attachment of a Triarylpentenedione to Poly(ethylene glycol)
Authors: Alvaro Mercedes , Aprile Carmela , García Hermenegildo , Peris Encarna 
Published: July 2005

Abstract3‐(4‐Aminophenyl)‐1,5‐diphenylpent‐2‐ene‐1,5‐dione (PDO) is a colorimetric sensor of Lewis acid cations that has been covalently attached to a poly(ethylene glycol) (PEG) scaffold. The resulting PDO‐PEG is soluble in water and other organic solvents and acts as a colorimetric sensor of Lewis acid cations by undergoing cyclization into the triarylpyrylium form. In water, PDO‐PEG also undergoes the colorimetric change in the presence of Brönsted acids, which may limit its usefulness. This modified PEG is recoverable by precipitation from cold ethanol and reusable after reopening of the triarylpyrylium heterocycle to the active pentenedione form. The testing‐recovery‐reuse cycle has been performed five times without noticeable differences in the response. In contrast to PDO‐PEG, PDO on its own is insoluble in water and remains completely soluble in ethanol. This solubility behavior of PDO makes the molecule unsuitable for use as a reusable and recoverable sensor. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
New Insights into the Reactivity of Nitrogen Dioxide with Substituted Phenols: A Solvent Effect
Authors: Astolfi Paola , Panagiotaki Maria , Greci Lucedio 
Published: July 2005

AbstractVarious alkyl‐substituted phenols react readily with nitrogen dioxide (·NO2) in different solvents at room temperature. In all cases nitration is the major reaction and leads to the formation of mono‐ and dinitrophenols and 4‐nitrocyclohexa‐2,5‐dienones from 2,4,6‐tri‐substituted phenols. Oxidation, dimerisation and, in one case, nitrosation are also observed. The reaction pathway followed changes according to the solvent and to the nature and the number of substituents on the phenolic ring. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
The First Chemical Synthesis of UDP[6‐3H]‐α‐D‐galactofuranose
Authors: Mariño Karina , Marino Carla , Lima Carlos , Baldoni Luciana , de Lederkremer Rosa M. 
Published: July 2005

AbstractGalactofuranose metabolism is a good target for the development of novel chemotherapeutic agents for the treatment of some microbial infections. This is a valid objective because galactofuranose is absent in mammals. Two enzymes are involved in the biosynthesis of molecules containing galactofuranose: a mutase, which catalyzes the interconversion of UDP‐Galp and UDP‐Galf, and D‐galactofuranosyltransferases. The mechanism of action of the mutase and its inhibition is currently being investigated, whereas studies on the galactofuranosyltransferases have been hampered by the lack of a labeled galactofuranose nucleotide. In the present work we describe the chemical synthesis of UDP‐α‐D‐[6‐3H]Galf and we prove its effectiveness for incorporation of radioactive galactofuranose into a natural acceptor. This is the first report on the chemical synthesis of a labeled donor of galactofuranose with the potential for studying the galactofuranosyltransferases independently from the UDP‐Galp mutase. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Enantioselective Synthesis of α‐Alkylmalates as the Pharmacophoric Group of Several Natural Alkaloids and Glycosides
Authors: El Bialy Serry A. A. , Braun Holger , Tietze Lutz F. 
Published: July 2005

AbstractA general enantioselective synthesis of α‐alkylmalates found in Cephalotaxus and Orchidaceae species is described. This preparation is based upon Seebach’s procedure for the alkylation of D‐malic acid with self‐regeneration of stereogenic centers. Reaction of the dioxolanone 8a with LiHMDS and allyl halides as well as benzyl bromide gave 10 and 14, respectively, which could be transformed into enantiopure α‐alkylmalates 13, 15, 18 and 19. In addition, enantiopure furans of type 20 have been prepared. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Diastereoselective Reactions of the Tiglic Acid Functionality Mediated by Oxazolidine Chiral Auxiliaries: A Mechanistic Comparison of DMD andm‐CPBA Epoxidations versus Singlet Oxygen and PTAD Ene Reactions
Authors: Pastor Aurelia , Adam Waldemar , Wirth Thomas , Tóth Gábor 
Published: July 2005

Abstract2,2‐Dimethyloxazolidines have been utilized as chiral auxiliaries for the diastereoselective functionalization of the optically active tiglic acid derivatives (S)‐1 by means of epoxidation with DMD or m‐CPBA and ene reactions with 1O2 or PTAD. In the DMD and m‐CPBA epoxidations, high diastereoselectivities but opposite senses of diastereomer selection were observed. In contrast, the stereochemistry of the 1O2 and PTAD ene reactions depended on the size of the attacking enophile: whereas essentially perfect diastereoselectivity was obtained with PTAD, much lower stereoselection was observed with 1O2. The stereochemical results for the DMD and m‐CPBA epoxidations and the PTAD ene reaction are explained in terms of the energy differences for the corresponding diastereomeric transition states, dictated by steric and electronic effects. The PTAD ene reaction for these tiglic acids (S)‐1 provides, after removal of the chiral auxiliaries, an attractive synthetic route for optically active β‐amino acid derivatives.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)