bluuebunny/crossref_metadata_2025_split huggingface dataset:
Facile Methods to Coat Polystyrene and Silica Colloids with Metal
Authors: Zhang J. , Liu J. , Wang S. , Zhan P. , Wang Z. , Ming N. 
Published: November 2004

AbstractTo avoid the complex core surface functionalization or pretreatment that is necessary in order to coat latex and silica colloids with a uniform, complete metal shell, the solvent‐assisted route has been explored to prepare a complete metal (Ag or Au) shell with controlled thickness on polystyrene (PS) colloids and the electroless plating approach, based on electrostatic attraction, has been explored to prepare a complete silver shell with controlled thickness on silica colloids. Without any additional surface treatment, the as‐prepared complex core–shell colloids can be crystallized directly into long‐range‐ordered structures with photonic bandgaps, as reported here for the first time. These ordered structures may find potential applications as substrates or physical systems for the enhancement of Raman scattering studies, besides applications as photonic crystals. The optical plasmon resonance of the composite core–shell colloids changes with metal shell thickness, the wavelength varying over hundreds of nanometers. Our coating routes are facile and versatile, and can be extended to coat PS and silica colloids with any other metal whose ion or complex can be reduced in solution.
Mechanistic and epidemiologic considerations in the evaluation of adverse birth outcomes following gestational exposure to statins
Authors: Edison Robin J. , Muenke Maximilian 
Published: November 2004

AbstractThe cholesterol‐lowering “statin” drugs are contraindicated in pregnancy, but few data exist on their safety in human gestation. We reviewed case reports for patterns suggesting drug‐related effects on prenatal development and considered a variety of mechanisms by which such effects, if confirmed, might occur. This uncontrolled case series included all FDA reports of statin exposures during gestation, as well as others from the literature and from manufacturers. Exposures and outcomes were reviewed and were tabulated by individual drug. Age‐specific rates of exposure to each drug among women of child‐bearing age were estimated. Of 214 ascertained pregnancy exposures, 70 evaluable reports remained after excluding uninformative cases. Among 31 adverse outcomes were 22 cases with structural defects, 4 cases of intrauterine growth restriction, and 5 cases of fetal demise. There were two principal categories of recurrent structural defects: cerivastatin and lovastatin were associated with four reports of severe midline CNS defects; simvastatin, lovastatin, and atorvastatin were all associated with reports of limb deficiencies, including two similar complex lower limb defects reported following simvastatin exposure. There were also two cases of VACTERL association among the limb deficiency cases. All adverse outcomes were reported following exposure to cerivastatin, simvastatin, lovastatin, or atorvastatin, which are lipophilic and equilibrate between maternal and embryonic compartments. None were reported following exposure to pravastatin, which is minimally present in the embryo. Statins reaching the embryo may down‐regulate biosynthesis of cholesterol as well as many important metabolic intermediates, and may have secondary effects on sterol‐dependent morphogens such as Sonic Hedgehog. The reported cases display patterns consistent with dysfunction of cholesterol biosynthesis and Sonic Hedgehog activity. Controlled studies are needed to investigate the teratogenicity of individual drugs in this class. © 2004 Wiley‐Liss, Inc.
Ice and water permittivities for millimeter and sub‐millimeter remote sensing applications
Authors: Jiang Jonathan H , Wu Dong L 
Published: November 2004

AbstractRecent advances in satellite remote sensing at near‐millimeter and sub‐millimeter wavelengths (∼100–3000 GHz) require accurate complex permittivity for ice and liquid water at these frequencies for different temperatures, especially for cold atmospheric conditions. This paper summarizes the existing experimental permittivity data in the literature and provides an updated empirical ice permittivity model for radiative transfer calculations for ground and space remote sensing experiments. Applications of this permittivity model to Microwave Limb Sounder (MLS) cloud measurements are discussed. Copyright © 2004 Royal Meteorological Society
Study of Substitution Limit, Structural, Bulk Magnetic and Electrical Properties of Ca2+ Substituted Magnesium Ferrite.
Authors: Chhaya S. D. , Pandya M. P. , Chhantbar M. C. , Modi K. B. , Baldha G. J. , Joshi H. H. 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Au2(SeO3)2(SeO4): Synthesis and Characterization of a New Noncentrosymmetric Selenite—Selenate.
Authors: Wickleder Mathias S. , Buechner Oliver , Wickleder Claudia , El Sheik Sherif , Brunklaus Gunther , Eckert Hellmut 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Facile Synthesis of Aminoalcohols by Ring Opening of Epoxides under Solvent‐Free Conditions.
Authors: Huerta Gloria , Contreras‐Ordonez Guadalupe , Alvarez‐Toledano C. , Santes Victor , Gomez Elizabeth , Toscano Ruben A. 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Photolysis of 1‐Alkylcycloalkanols in the Presence of (Diacetoxyiodo)benzene and I2. Intramolecular Selectivity in the β‐Scission Reactions of the Intermediate 1‐Alkylcycloalkoxyl Radicals.
Authors: Antunes Carla S. Aureliano , Bietti Massimo , Lanzalunga Osvaldo , Salamone Michela 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Development of a Continuous‐Flow System for Catalysis with Palladium(0) Particles.
Authors: Solodenko Wladimir , Wen Hongliang , Leue Stefanie , Stuhlmann Friedrich , Sourkouni‐Argirusi Georgia , Jas Gerhard , Schoenfeld Hagen , Kunz Ulrich , Kirschning Andreas 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Alkoxy Group Facilitated Ring Closing Metathesis (RCM) of Acyclic 1,6‐Dienes. Convenient Synthesis of Non‐racemic Highly Substituted Cyclopentenols.
Authors: Nayek Abhijit , Banerjee Shyamapada , Sinha Saikat , Ghosh Subrata 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
A Copper‐ and Amine‐Free Sonogashira Reaction Employing Aminophosphines as Ligands.
Authors: Cheng Jiang , Sun Yanhui , Wang Feng , Guo Minjie , Xu Jian‐Hua , Pan Yi , Zhang Zhaoguo 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Palladium Charcoal Catalyzed Deprotection of O‐Allylphenols.
Authors: Ishizaki Miyuki , Yamada Makoto , Watanabe Shin‐ichi , Hoshino Osamu , Nishitani Kiyoshi , Hayashida Maiko , Tanaka Atsuko , Hara Hiroshi 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
3‐Chloro‐2‐methylphenyl‐Substituted Semicarbazones: Synthesis and Anticonvulsant Activity.
Authors: Yogeeswari Perumal , Thirumurugan Rathinasabapathy , Kavya Ramkumar , Samuel Jayakar Selwyn , Stables James , Sriram Dharmarajan 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
An Efficient and Environment Friendly Procedure for the Synthesis of Arylmethylenemalononitrile Catalyzed by Strong Base Anion‐Exchange Resin in Water.
Authors: Jin Tong‐Shou , Zhang Jian‐She , Wang Ai‐Qing , Li Tong‐Shuang 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Thiazolecarboxylic Acid Derivatives. Part 1. N‐Substituted 2‐Amino‐4‐methylthiazole‐5‐carboxylic Acid Derivatives.
Authors: Dovlatyan V. V. , Eliazyan K. A. , Pivazyan V. A. , Kazaryan E. A. , Engoyan A. P. 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
A Novel Synthesis of Tri‐ and Tetra‐phenylpyrylium Perchlorates from Phenyl‐Substituted Cyclopentadienes.
Authors: Gong Wei‐Tao , Li Xin‐Cheng , Ning Gui‐Ling , Lin Yuan 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Synthesis of Five‐, Six‐, and Seven‐Membered Ring Lactams by Cp*Rh Complex‐Catalyzed Oxidative N‐Heterocyclization of Amino Alcohols.
Authors: Fujita Ken‐ichi , Takahashi Yoshinori , Owaki Maki , Yamamoto Kazunari , Yamaguchi Ryohei 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Synthesis of Quinolines, 2‐Quinolones, Phenanthridines, and 6(5H)‐Phenanthridinones via Palladium[0]‐Mediated Ullmann Cross‐Coupling of 1‐Bromo‐2‐nitroarenes with β‐Halo‐enals, enones, or ‐esters.
Authors: Banwell Martin G. , Lupton David W. , Ma Xinghua , Renner Jens , Sydnes Magne O. 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Synthesis and anti‐HIV‐1 Activity of 2‐[2‐(3,5‐Dimethylphenoxy)ethylthio]pyrimidin‐4(3H)‐ones.
Authors: Novikov M. S. , Ozerov A. A. , Sim O. G. , Buckheit R. W. 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Heterocyclization of Functionalized Heterocumulenes with C,N‐ and C,O‐Binucleophiles. Part 1. Cyclocondensation of 1‐Chloroalkylheterocumulenes and N‐(1‐Chloroalkylidene)urethanes with 2‐Cyanomethylpyridine.
Authors: Vovk M. V. , Lebed P. S. , Chernega A. N. , Pirozhenko V. V. , Boiko V. I. , Tsymbal I. F. 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Condensed Pyridopyrimidines. Part 7. Synthesis of Condensed Triazolo[4,3‐c]‐ and Tetrazolo[1,5‐c]pyrimidines.
Authors: Oganisyan A. Sh. , Noravyan A. S. , Grigoryan M. Zh. 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Condensed Thienopyrimidines. Part 19. Study of the Heterocyclization of 2‐Hydrazino‐6,6‐dimethyl‐5,6‐dihydro‐8H‐pyranothieno [2,3‐d]pyrimidin‐4‐one.
Authors: Oganisyan A. Sh. , Noravyan A. S. , Karapetyan A. A. , Aleksanyan M. S. , Struchkov Yu. T. 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Peribysins A—D, Potent Cell‐Adhesion Inhibitors from a Sea Hare‐Derived Culture of Periconia Species.
Authors: Yamada Takeshi , Iritani Masashi , Minoura Katsuhiko , Kawai Kenzo , Numata Atsushi 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Synthesis and Biological Activity of 22‐Oxa CD‐Ring Modified Analogues of 1α,25‐Dihydroxyvitamin D3: cis‐Perhydrindane CE‐Ring Analogues.
Authors: Demin Samuel , Van Haver Dirk , Vanderwalle Maurits , De Clercq Pierre J. , Bouillon Roger , Verstuyf Annemieke 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
An Expeditious Total Synthesis of Kalkitoxins: Determination of the Absolute Stereostructure of Natural Kalkitoxin.
Authors: Yokokawa Fumiaki , Asano Toshinobu , Okino Tatsufumi , Gerwick William H. , Shioiri Takayuki 
Published: November 2004

AbstractFor Abstract see ChemInform Abstract in Full Text.
Prognostic factors in oral cavity and oropharyngeal squamous cell carcinoma
Authors: Marcus Benjamin , Arenberg Douglas , Lee Julia , Kleer Celina , Chepeha Douglas B. , Schmalbach Cecelia E. , Islam Mozaffarul , Paul Supriti , Pan Quintin , Hanash Samir , Kuick Rork , Merajver Sofia D. , Teknos Theodoros N. 
Published: November 2004

AbstractBACKGROUNDThe survival of patients with head and neck squamous cell carcinoma (HNSCC) remains unaffected despite recent therapeutic advances. To reverse this trend, reliable and clinically applicable markers of tumor aggressiveness must be identified. One such marker may be the tumor‐associated macrophage content. The authors hypothesized that tumor‐associated macrophages contribute to HNSCC aggressiveness, and the objective of the current study was to prove this hypothesis using mRNA expression analysis and a large cohort of clinical specimens.METHODSOligonucleotide microarray analysis was performed on a prospective cohort of 20 patients with previously untreated oral cavity or oropharynx squamous cell carcinoma (OC/OP SCCA) and on normal oropharyngeal mucosa from 4 patients. After determining whether macrophage chemoattractants were produced by tumors, conditioned media from three HNSCC cell lines were used to quantify macrophage migration in an in vitro assay. A high‐density tissue microarray of 102 patients with previously untreated OC/OP SCCA was stained immunohistochemically for CD68 to identify tissue macrophages, and the results were correlated with clinicopathologic data and survival.RESULTSMonocyte chemoattractant protein 1 was up‐regulated significantly in tumors compared with normal mucosa (P = 0.0025; fold change = 1.89). All University of Michigan SCC tumor cell line conditioned media caused a significant increase in macrophage migration (P < 0.05). Tissue microarray data revealed that macrophage content of the primary tumor was associated strongly with lymph node metastasis (P < 0.0001), extracapsular lymph node spread (P = 0.0001), and advanced clinical disease stage (P = 0.0002). When it was evaluated along with other clinicopathologic data, the macrophage content was found to be an independent predictor of lymph node metastasis (P < 0.0001).CONCLUSIONSPrimary tumor macrophage content is a strong predictor of tumor aggressiveness in HNSCC. Cancer 2004. © 2004 American Cancer Society.
Nonquenchable Chemical Order−Disorder Phase Transition in Yttrium Oxyfluoride
Authors: Levin Igor , Huang Qing Z. , Cook Lawrence P. , Wong‐Ng Winnie 
Published: November 2004

AbstractA chemical order−disorder polymorphic phase transition in yttrium oxyfluoride (YOF) was studied in situ by X‐ray and neutron powder diffraction. The high‐temperature form of YOF crystallizes with a cubic Fm$\bar 3$
m fluorite structure in which the O and F atoms are disordered among the tetrahedrally coordinated sites. The low‐temperature form of YOF exhibits rhombohedral R$\bar 3$
m symmetry and evolves from the high‐temperature form by the phase transition associated with the ordering of the O and F atoms. The transition occurs around 560 °C. The superstructure contains layers of [OY4] and [FY4] tetrahedra alternating along the c‐axis of the trigonal cell (parallel to the <111> direction of the parent cubic structure). The ordering of the O and F atoms is accompanied by the significant displacements of the Y, O, and F atoms from their ideal positions in the cubic phase. Bond valence sum calculations indicate considerable bond strain for both O and F in the cubic structure; the strain is relieved in the ordered low‐temperature phase. The order−disorder transition in YOF is completely reversible and exhibits fast nonquenchable kinetics. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Synthesis, Structure, and Photophysical and Electrochemical Properties of Cyclometallated Iridium(III) Complexes with Phenylated Bipyridine Ligands
Authors: Lepeltier Marc , Kwok‐Ming Lee Terence , Kam‐Wing Lo Kenneth , Toupet Loic , Le Bozec Hubert , Guerchais Véronique 
Published: November 2004

AbstractA series of cationic diiminoiridium(III) complexes [Ir(ppy‐N,C)2(L‐N,N)](PF6) has been prepared [Hppy = 2‐phenylpyridine; L = 4,4′‐tBu2dpbpy (1), 4,4′‐Me2dpbpy (2), 4,4′‐Me2pbpy (3), 4,4′‐Me2bpy (4)] and their photophysical and electrochemical properties studied. X‐ray diffraction studies of complex 1 reveal a dihedral angle of about 33° between the pyridine rings, and that the two phenyl groups are also tilted with respect to the adjacent pyridine rings. All the complexes exhibit moderately intense and long‐lived emission. The origin of the emission is tentatively assigned to a triplet metal‐to‐ligand charge‐transfer 3MLCT [dπ(Ir) → π*(diimine)] excited state, although the possibility of a triplet σ‐bond‐to‐ligand charge transfer 3SBLCT [σ(Ir−C) → π*(diimine)] cannot be excluded. The luminescence properties of the complexes are dependent on the substituents on the diimine ligands. Selective N‐methylation of the diimine ligands has been achieved and their N,C‐coordination to the Ir centre has been attempted. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Rearrangement of the Active Ester Intermediate During HOBt/EDC Amide Coupling
Authors: Mahmoud Khaled A. , Long Yi‐Tao , Schatte Gabriele , Kraatz Heinz‐Bernhard 
Published: November 2004

Abstract3‐{[1′‐(tert‐Butyloxycarbonylamino)ferrocen‐1‐yl]carbonyl}benzotriazole 1‐oxide (3) has been successfully separated during the synthesis of benzotriazol‐1‐yl 1′‐(tert‐butyloxycarbonylamino)ferrocene‐1‐carboxylate (2) as an active ester for peptide coupling. The yield of 3 increased by using polar, rather than nonpolar solvents. The two compounds have been fully characterized and studied by X‐ray crystallography and spectroscopic methods. The active ester derivative 2 formed a urethane bond with the glycine ethyl ester while the N‐oxide 3 did not react. The X‐ray structural analysis of 3 shows strong intermolecular hydrogen bonding involving the urethane group and the N‐oxide of an adjacent molecule [N−O···H−N = 2.859(2) Å]. No hydrogen bonding is present in the solid state for compound 2, while solution studies indicate the presence of intramolecular hydrogen bonding. Both complexes display a quasi‐reversible single one‐electron oxidation, the halfwave potentials E1/2 for 2 and 3 were 672 ± 5 and 591 ± 5 mV, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Synthesis and Conformational Analysis of Macrocycles Related to 10‐Oxa‐epothilone
Authors: Quintard Delphine , Bertrand Philippe , Bachmann Christian , Gesson Jean‐Pierre 
Published: November 2004

AbstractA short and convergent synthesis of macrocyclic lactones related to 10‐oxa‐epothilone is based on aldolisation of a 3‐(2′‐methylallyloxy) aldehyde derived from methyl (2S)‐3‐hydroxy‐2‐methylpropionate followed by ring‐closing metathesis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
The Effects of Space Formed by Host Molecules in Inclusion Compounds on the Homogeneity/Heterogeneity of the Photoreaction in the Solid State
Authors: Lavy Tali , Sheynin Yana , Kaftory Menahem 
Published: November 2004

AbstractTwo inclusion compounds that contain a light‐stable host molecule and a light‐sensitive guest molecule have been crystallized, that is, 4,5‐bis(hydroxydiphenylmethyl)‐2,2‐dimethyl‐1,3‐dioxolane as the host molecule with tropolone methyl ether as the guest molecule and 2,3‐bis(hydroxydiphenylmethyl)‐1,4‐dioxaspiro[4.5]decane as the host molecule with 4‐(oxophenylacetyl)morpholine as the guest molecule. The two inclusion compounds undergo photochemical ring‐closure reactions. However, while the first reacts by a heterogeneous process, the second undergoes a homogeneous photoreaction. The X‐ray crystal structure of the two compounds clearly demonstrate that when the space required by the guest molecule to undergo the photoreaction fits the space provided by the host molecule, the reaction is homogeneous; when the space required by the guest is larger than that provided by the host molecule, the photoreaction is heterogeneous. Since the photochemical reaction of the inclusion compound with tropolone methyl ether as the guest is heterogeneous it could not be followed by single‐crystal X‐ray diffraction. The product of the photochemical reaction is 1‐methoxybicyclo[3.2.0]hepta‐3,6‐dien‐2‐one. The photochemical reaction of the second compound was followed by single‐crystal X‐ray diffraction and the crystal structure shows that the product is tetrahydro‐2‐phenyloxazolo[2,3‐c][1,4]oxazine‐3(2H)‐one, and not the β‐lactam system obtained in similar reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
One‐Step Synthesis of Novel Flavylium Salts Containing Alkyl Side Chains in Their 3‐, 4′‐, 5‐ or 6‐Positions and Their Photophysical Properties in Micellar Media
Authors: Fernandes Ana C. , Romão Carlos C. , Rosa Carla P. , Vieira Vera P. , Lopes António , Silva Palmira F. , Maçanita António L. 
Published: November 2004

AbstractA one‐step preparation of several flavylium salts containing alkyl side chains in their 3‐, 4′‐, 5‐ or 6‐positions is described. Flavylium salts with alkyl side chains in positions 3 or 4′ were isolated from reactions between 2,4‐dihydroxybenzaldehyde and decanophenone, dodecanophenone and 4′‐hexyl‐ or 4′‐dodecylacetophenone. Flavylium salts with alkyl side chains in positions 5 or 6 were prepared through reactions between benzoylacetone and 4‐hexyl‐, 4‐dodecyl‐ or 5‐pentylresorcinol. The new compounds are insoluble or sparingly soluble in water, but readily incorporate into aqueous dispersions of anionic (SDS), cationic (CTAB) or neutral (C12E10) surfactants above their critical micellar concentrations. They also present interesting spectroscopic properties − namely, ultra‐fast proton transfer in the excited state − and the 4′ derivatives also exhibit photochromic behaviour, which might have several applications in the field of self‐assembled systems. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
The Aromatic CH/π Hydrogen Bond as an Important Factor in Determining the Relative Stability of Diastereomeric Salts Relevant to Enantiomeric Resolution − A Crystallographic Database Study
Authors: Suezawa Hiroko , Ishihara Shinji , Umezawa Yoji , Tsuboyama Sei , Nishio Motohiro 
Published: November 2004

AbstractA systematic study was carried out to understand the principle underlying the process of enantiomeric resolution by the use of the Cambridge Structural Database. The crystal structures of fourteen pairs of diastereomeric salts, containing the mandelate anion, or its analogues, as the chiral acid component, were analyzed in the context of the aromatic CH/π hydrogen bond. The mean aromatic C−H···π distance parameters of the less‐soluble salts are shorter than in the more‐soluble ones. Also, the C−H···π‐ring access angle, on average, is more acute in the less‐soluble salts than in the more‐soluble ones. Nontrivial discrepancies, on the other hand, have been noted in case‐by‐case comparisons of the parameters of several pairs. It was concluded that the contribution from the aromatic CH/π hydrogen bond should at least be taken into account when considering enantiomeric separation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Oxidation of Δ4‐ and Δ5‐Steroids with Hydrogen Peroxide Catalyzed by Porphyrin Complexes of MnIII and FeIII
Authors: Rebelo Susana L. H. , Simões Mário M. Q. , Neves M. Graça P. M. S. , Silva Artur M. S. , Cavaleiro José A. S. , Peixoto Andreia F. , Pereira Mariette M. , Silva Manuela R. , Paixão José A. , Beja Ana M. 
Published: November 2004

AbstractIn this paper we describe a new environmentally friendly method to promote the stereoselective epoxidation of Δ4‐ and Δ5‐steroids. Metalloporphyrins efficiently catalyze the epoxidation reactions of 17β‐acetoxy‐4‐androstene (1), 4‐cholestene (2) and 3β‐acetoxy‐5‐cholestene (3) in the presence of H2O2 as oxygen donor. Modeling the molecular structure of the porphyrin as well as the central metal allows the control of the preferential formation of α‐ or β‐epoxides. Porphyrins with bulky, electron‐withdrawing groups in the ortho positions of the meso phenyls and with MnIII as the central metal ion, such as [Mn(TDCPP)Cl], gave preferentially the β‐epoxide of Δ4‐ and Δ5‐steroids. [Fe(TPFPP)Cl] catalyzes preferentially the α‐epoxidation of Δ4‐steroids and also increases the stereoselectivity for the α‐epoxide in Δ5‐steroids, similar to the results obtained with m‐CPBA (m‐chloroperbenzoic acid) as oxidant. The substrate structure strongly influences the chemoselectivity of the reactions. The X‐ray structures of two main products were determined, and two‐dimensional NMR techniques allowed the full assignment of 1H and 13C NMR resonances as well as the stereochemistry of these products. A mechanistic proposal involving oxo species for the β‐approach and peroxy species for the α‐approach is proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)