bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Chemical Transformations of 4, 5‐Homosnoutene Derivatives: An Attempted New Access onto the (CH)12 Energy Hypersurface
Authors: Kirchmeyer Stephan , De Meijere Armin 
Published: December 2004

AbstractPentacyclo[6. 4. 02, 4. 03, 10. 07, 9]dodeca‐5, 11‐diene(4) is proposed as new potential precursor of the truncated tetrahedrane 1. The synthesis of several new pentacyclo[5. 4. 0. 02, 4. 03, 9. 06, 8] undec‐10‐ene (4, 5‐homosnoutene) derivatives including homosnouten‐5‐one(10), 5‐methylidenehomosnoutene(19a) as well as homosnoutene‐5‐carb‐aldehyde(17b) and their reactions directed toward ring enlargement to the skeleton of 4 are reported. Although all the homosnoutenes resisted ring expansions, several unexpected new polycyclic systems were obtained. Any intermediate developing a cationic center at C(5) of the skeleton of 10 rearranged with release of strain and opening of one or both three‐membered rings to give compounds such as 22 and 23. The aminomethyl derivatives 13a and 13b, upon diazotation, underwent a remarkable fragmentation to give 10 and homosnouten‐5‐o1(20), respectively. The 5‐(dibromomethyl) homosnouten‐5‐o1(14), upon treatement with t‐BuLi, rearranged to the pentacyclic ether 15, while the carbine 11b, generated by the thermal or photochemical decomposition of the tosylhydrazone salt of 17c, solely gave 19a by C, H insertion. The 1, 1‐dicyclopropylethene unit in 19c was excited selectively upon irradiation, but the products 26 and 27 of this photochemical rearrangement were derived only from n‐participation in diradical intermediates 25a‐25c.
Electronic and Steric Influence of Axial and Equatorial Ligands in Vitamin B12 Model Complexes Derived from Cobaloxime: Electrochemical and 59Co‐NMR Studies
Authors: Tavagnacco Claudio , Balducci Gabriele , Costa Giacomo , Täschler Karl , von Philipsborn Wolfgang 
Published: December 2004

AbstractIn four series of strictly related organocobalt complexes, derived from cobaloximes by replacement of the O…H…O with O…‐BF2…O and/or (CH2)3 groups, the trends of 59Co‐NMR shielding and electrochemical data are discussed. A largely parallel behaviour of the plots of E1/2(I) values for the first Co(III)/Co(II) electron transfer vs. the 59Co chemical shifts reflects the similar sensitivity of the two parameters to a change in electron affinity of the central metal ion due to a variation of the organic group R. E1/2(II) values for the second Co(II)/CO(I) electron transfer are less sensitive to the change of R, but the trend of the plot vs. δ(59Co) is still parallel in the four series. Consistent deviations from a roughly linear dependence of E1/2(I) on pKa of the hydrocarbon acid corresponding to R, on Taft constant s̀* and on 59Co shielding are noticed for the isopropyl derivatives and attributed to a steric effect. This was confirmed in a series of RCo(DMG)pyridine complexes in which 59Co shielding decreases steadily with increasing steric parameter Es (Taft) of the alkyl group. There is experimental evidence from X‐ray data that δ(59Co) decreases with an increase of the CoC bond length, illustrating steric hindrance in alkyl coordination to be responsible for the decreased shielding of the 59Co nucleus. The relative displacements of the graphic displays for the different series reflect the effect of changes in electron affinity of the redox center, due to the equatorial ligand, which, in turn, is caused by variations in the electron‐withdrawing power due to the introduction of the BF2 group and by the change from −2 to −1 valence of the (CH2)3‐capped ligands.
Synthesis of Cationic 2,4‐Dimethylpenta‐2,4‐dienylruthenium Complexes. Crystal Structure of Carbonyl(η4‐cyclohexa‐1,3‐diene)‐(η5‐2,4‐dimethylpenta‐2,4‐dienyl)ruthenium Tetrafluoroborate
Authors: Lumini Tito , Cox David N. , Roulet Raymond , Chapuis Gervais , Nicolo Francesco 
Published: December 2004

AbstractThe complex [Ru(η5‐C7H11)2H]BF4 (C7H11 = 2,4‐dimethylpenta‐2,4‐dienyl) is highly reactive towards two‐ and six‐electron ligands. e.g. giving with CO complex [RuCO(η4‐C7H12)(η5‐C7H11)]BF4. The 2,4‐dimethylpenta‐1,3‐diene ligand (C7H12) of the latter complex is readily displaced giving, e.g. with excess cyclohexa‐1,3‐diene (C6H8) complex [RuCO(η4‐C6H8)(η5‐C7H11)]BF4. These reactions provide a convenient entry into monopentadienylruthenium chemistry.
Kinetic and thermodynamic parameters for Schiff‐rase formation between 5′‐deoxypyridoxal and hexylamine
Authors: Vazquez Miguel A. , Donoso Josefa , Muñoz Francisco , Blanco Francisco Garcia , del Vado M. Angeles Garcia , Echevarria Gerardo 
Published: December 2004

AbstractThe thermodynamic parameters involved in the formation of Schiff bases between 5′‐deoxypyridoxal and hexylamine were determined at different pH values and a constant ionic strength (0.1 M). The overall and individual rale constants of formation and hydrolysis at 10, 15, 20, 25, and 30° were also determined. The enthalpy of the overall formation process was found to be negative at all the pH values assayed except the neutral, while its entropy was always positive. The results obtained show the great relevance of the phosphate group at C(5′) to the stabilization of the Schiff bases of pyridoxal 5′‐phosphate.
Studies Directed Towards the Biosynthesis of the C7N Unit of Rifamycin B: A New Synthesis of Quinic Acid from Shikimic Acid
Authors: Meier Rose‐Marie , Tamm Christoph 
Published: December 2004

AbstractThe synthesis of quinic acid (4) via epoxide 13, starting from shikimic acid (5), is described (Scheme 1). Treatment of 13 with thiophenol yielded not only 17, but also the γ‐lactones 18 and 19 as result of migration of silyl groups within a cis‐ and trans‐diol system. The conversion provides a direct stereoselective epoxidation of a shikimic‐acid derivative as well as an alternative pathway for the preparation of 4. A shorter approach via the disilylated epoxide 22 was unsuccessful because the γ‐lactone 25 was obtained in place of the desired α‐hydroxy ester 24 (Scheme 2).
Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)‐3,6:3′,6′‐Diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotin‐5,5′‐diol), ein neues Carotinoid aus Paprika (Capsicum annuum)
Authors: Deli Jóseph , Mólnar Péter , Tóth Gyula , Baumeler Andreas , Eugster Conrad Hans 
Published: December 2004

Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)‐3.6:3′,6′‐Diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐5,5′‐diol), a Novel Carotenoid from Red Paprika (Capsicum annuum)From red paprika (Capsicum annuum var. longum nigrum) cycloviolaxanthin was isolated as a minor carotenoid and, based on spectral data, assigned the symmetrical structure 8.
Double‐Diamond Inclusion Compounds of 2,6‐Dimethylydeneadamantane‐1,3,5,7‐tetracarboxylic Acid
Authors: Ermer Otto , Lindenberg Lorenz 
Published: December 2004

AbstractThe crystal structures of four inclusion compounds of 2,6‐dimethylideneadamantane‐1,3,5,7‐tetracarboxylic acid (4) are described, which involve the following guest species: (a) a mixture of 4‐methylpent‐3‐en‐2‐one, 2,6‐dimethylhepta‐2,5‐dien‐4‐one, and mesitylene (condensation products of acetone); (b) mesitylene; (c) a mixture of 4‐methylpent‐3‐en‐2‐one and mesitylene; (d) (tert‐butyl)benzene. In all four cases, the host architectures consist of two interpenetrating super‐diamond networks built up by the tetra‐acid molecules via pairwise H‐bonds between the tetrahedrally directed COOH groups. In the first three cases (tetragonal crystal symmetry), the two diamond‐like host lattices interpenetrate symmetrically, in the fourth case (monoclinic) asymmetrically. This asymmetry is brought about by the increased steric bulk of the (tert‐butyl)benzene guest molecules. Attempts to enforce an inclusion compound of 4 with a single, extremely hollow diamond‐like host lattice by offering still bulkier guest molecules have as yet not been met with success. The generally very high propensity of 4 to form inclusion compounds was envisaged and designed beforehand by appropriate evaluation and modulation of the crystal structure of the parent adamantane‐1,3,5,7‐tetracarboxylic acid, which represents a fivefold diamond‐like self‐inclusion compound. Crystals of the free, uncomplexed 4 appear to be extremely unstable and could so far not be obtained. On the other hand, from aqueous solution a very stable monohydrate of 4 may be crystallized (4‐H2O), which was also subjected to X‐ray analysis. The (triclinic) crystal structure of 4·H2O involves an interesting dichotomy inasmuch its pattern of H‐bonding may be rationalized either in terms of a double, cross‐linked super‐zincblende (sphalerite) architecture, or as a system of porous, puckered 4‐connected sheets, which interpenetrate each other pairwise and are cross‐linked by the H2O molecules. Various structure and (space group) symmetry characteristics of the supramolecular solid‐state complexes reported here are highlighted by pointing out analogies with comparable structures retrieved from the literature.
Ruthenium(II) Complex of the Alkaloid 2‐Bromoleptoclinidinone. Preparation and Interaction with Double‐Stranded DNA
Authors: Goullc Véronique , Lehn Jean‐Marie , Schoentjes Bruno , Schmitz Francis J. 
Published: December 2004

AbstractThe fused pentacyclic alkaloid 2‐bromoleptoclinidinone (1) isolated from an ascidian possesses a bidentate chelating site. Complexation of 1 with [cis‐RuCl2{(D8)bpy}2] · 2H2O forms an octahedral complex which was isolated both as hexafluorophosphate 2 and chloride 3 salts. Intercalation of 3 in calf‐thymus DNA was shown to occur as well as photoactivated cleavage of double‐strand supercoiled DNA pBR322 under visible‐light irradiation.
1,3‐Oxathiolan‐Synthese: Spirocyclische 1,3‐Oxathiolane aus der Lewis‐Säure‐katalysierten Umsetzung von cyclischen Trithiocarbonaten und Oxiranen
Authors: Oremus Vladimir , Linden Anthony , Heimgartner Heinz 
Published: December 2004

1,3‐Oxathiolanc Synthesis: Spirocyclic 1,3‐Oxathiolanes from the Lewis‐Acid‐Catalyzed Reaction of Cyclic Trithiocarbonates and OxiranesThe cyclic trithiocarbonates 1.3‐dithiolane‐2‐thione (4) and 1,3‐dithiole‐2‐thione (9) in 1,2‐dichloroethane and MeCN, respectively, react with alkyl‐ and phenyl‐substituted oxiranes 2 in the presence of Lewis acids to give 1‐oxa‐4,6,9‐trithiaspiro[4.4]nonanes 5 and 6 (Scheme 2) and 1‐oxa‐4,6,9‐trithiaspiro[4.4]non‐7‐enes 10 and 11 (Scheme 3), respectively. The reactions proceed regioselectively yielding 2‐alkyl (5, 10) and 3‐phenyl derivatives (6, 11) as the main products. From the reaction of 4 and 2‐phenyloxirane (2e) with TiCl4, 2‐phenyl‐1,4,6,9‐tetrathia‐spiro[4.4]nonane (7) is isolated as a minor product. The molecular structures of 5a, 6e, and 7 are established by X‐ray crystallography.
SN2 or Electron Transfer?? A new technique discriminates the mechanisms of oxidative addition of alkyl halides to corrinato‐ and porphyrinatocobalt(I)
Authors: Zhou De‐Ling , Walder Peristera , Scheffold Rolf , Walder Lorenz 
Published: December 2004

AbstractA fast electrochemical technique for the discrimination of one‐ and two‐electron mechanisms in the oxidative addition of alkylating agents (RX) to corrinato‐ and porphyrinatocobalt(I) ([CoIL]) is described. It is based on single‐scan voltammograms of [CoIIL] in the presence of RX and variable amounts of the radical trap acrylonitrile. In the first part of the voltammogram, [CoIIL] is reduced, and fast oxidative addition of RX to [CoIL] is triggered. If the reaction proceeds via a two‐electron mechanism, [RCoIIIL] is formed independently of acrylonitrile concentration, but if a transient free radical R is involved, R is competitively trapped by acrylonitrile and [CoIIL] to yield, at high enough acrylonitrile concentration, exclusively the olefin‐inserted [RCNCoIIIL]. [RCNCoIIIL] is reducible in the intermediate potential range, [RCoIIIL] at the negative end of the single‐scan voltammogram. Hence, from the appearance of the reduction waves due to [RCNCoIIIL] and [RCoIIIL], the mechanism of oxidative addition of RX to [CoIL] is easily deduced. The method is applied to the study of the mechanistic borderline of oxidative addition using a series of 15 RX and 4 [CoL]'s, i.e. cobalamin (Cbl), heptamethyl cobyrinate (‘Cby’), (tetraphenylporphyrinato) cobalt ([Co(tpp])), and (octaethylporphyrinato) cobalt ([Co(oep)]). All non‐activated primary alkyl iodides and bromides exhibit, at room temperature, pure two‐electron mechanisms with all [CoIL]'s, except neopentyliodide with Cb1I and ‘Cby’I. All secondary alkyl iodides involve free radicals with Cb1I and ‘Cby’I, but a pure two‐electron mechanism or a mixed one‐electron two‐electron mechanism with [CoI(tpp)] and [CoI(oep)]. The mechanistic switch from a two‐electron to a one‐electron mechanism for increasingly sterically demanding RX's occurs earlier with the supernucleophilic Cb1I and ‘Cby’I than with [CoI(tapp)] and [CoI(oep)].
Axially Dissymmetric diphosphines in the Biphenyl Series: Crystal structures of three new group‐VIII metal complexes of (6,6′‐dimethyl‐1,1′‐biphenyl‐2,2′‐diyl)bis(diphenylphosphine) ( = biphemp)
Authors: Knierzinger Andreas , Schönholzer Peter 
Published: December 2004

Abstract(6,6′‐Dimethyl‐1,1′‐biphenyl‐2,2′‐diyl)bis(diphenylphosphine) ( = biphemp) reacts with allymetal halidesm to yeild complexes 1–3 which were transformed into the corresponding perchlorates 4–6. The molecular structures of 4–6 were determined by X‐ray analyses.
Synthesis and Properties of Macrobicyclic Cryptates Incorporating Five‐ and Six‐Membered Biheteroaryl Units
Authors: Lehn Jean‐Marie , De Vains Jean‐Bernard Regnouf 
Published: December 2004

AbstractThe socium cryptates of the macrobicyclic ligands 1–6 have been synthesized by direct macrobicyclisation or by stepwise procedures. They incorporate 2,2′‐bithiazole, 2,2′‐biimidazole, 2.2′‐bipyrimidine as well as 2,2′‐bipyridine units. Treatment of the sodium complexes with europium(III) chloride gave the corresponding EuIII cryptates. The structural and spectral properties of these compounds are described. The EuIII complexes present characteristic 1H‐NMR chemical‐shift features. Their luminescence properties are described.
A Short Syntheses of 1,2‐Dimethylazulenes
Authors: Fallahpour Reza Ali , Hansen Hans‐Jürgen 
Published: December 2004

AbstractDimethyl azulene‐1,2‐dicarboxylates are reduced with a 4–5 molar excess of DIBAH in Et2O/hexane at 0° to yield the corresponding 2‐(hydroxymethyl)‐1‐methylazulenes which can be further reduced to 1,2‐dimethylazulenes on treatment with Et3SiH in TFA at 60° (cf. the Table).
Synthesis of Phosphonates and Oligodeoxyribonucleotides Derived from 2′‐Deoxyisoguanosine and 2′‐Deoxy‐2‐haloadenosines
Authors: Seela Frank , Mertens Ralf , Kazimierczuk Zygmunt 
Published: December 2004

AbstractOligonucleotides containing 2′‐deoxyisoguanosine (1) or 2‐chloro‐2′‐deoxyadenosine (2a) have been prepared by solid‐phase synthesis. Suitably protected phosphonates 3a, 4a, and 4b as well as the phosphoramidite of 1 have been obtained from the nucleosides 1, 2a, or 2b via the (dimethylamino)methylidene derivatives 5–7. 4,4′‐Dimethoxytrityl groups were introduced to yield the base‐protected derivatives 8–10. Alternatively to the direct incorporation of 1 into oligonucleotides, they were also obtained by the photochemical conversion of a 2a residue within the oligonucleotide chain.
Total Synthesis of the Gastroprotective Substance AI‐77‐B and of Analogues
Authors: Durgant Jean‐Marc , Vogel Pierre 
Published: December 2004

AbstractThe Diels‐Alder adducts 8 of furan to 1‐cyanovinyl acetate were converted into (Methyl 3‐chloro)‐5‐O‐(3‐chlorobenzoyl)‐2, 3‐dideoxy‐α‐dl‐arabino‐hexofuranosid)uronic acid ((α)‐18a) and into (methyl 3‐azido‐5‐O‐(3‐chlorobenzoyl_‐2,3‐dideoxy‐α‐dl‐ribo‐hexofuranosid)uronic acid ((α)‐41a). These compounds were condensed to (3S)‐3‐[(1′S)‐1′‐amino‐3′‐methylbutyl]‐3,4‐dihydro‐8‐hydroxyisocoumarin hydrochloride ((−)‐2); the resulting mixtures of diastereoisomeric amides were transformed and separated to give the gastroprotective substance AI‐77‐B((−)‐1) and analogues.
C2‐Symmetrical Pyrrolidine Derivatives Chiral Auxiliaries in Radical Chemistry
Authors: Veit Andres , Lenz Roman , Seiler Martin E. , Neuburger Markus , Zehnder Margareta , Giese Bernd 
Published: December 2004

AbstractFumaramides 3b and 3c bearing the C2‐symmetrical pyrrolidine moieties (2R,5R)‐2,5‐bis(methoxymethyl)pyrrolidine (2b) or 1,3:4,6‐di‐O‐benzylidene‐2,5‐dideoxy‐2,5‐imino‐L‐idit (2c), respectively, as a chiral auxiliary lead to high diastereoselectivities in radical reactions (‘tin method’;Scheme 1). Removal of the chiral auxiliaries affords the corresponding alkylated fumaric acids Scheme 2. Single‐crystal X‐ray structures of 3b and 3c support arguments that lead to the model of 1,4‐stereoinduction.
Nucleic‐Acid Analogues with Constraint Conformational Flexibility in the Sugar‐Phosphate Backbone (‘Bicyclo‐DNA’). Part 1. Preparation of (3S,5′R)‐2′‐Deoxy‐3′,5′‐ethano‐αβ‐D‐ribonucleosides (‘Bicyclonucleosides’)
Authors: Tarköy Markus , Bolli Martin , Schweizer Bernd , Leumann Christian 
Published: December 2004

AbstractWe describe the synthesis of 2′‐deoxy‐3′,5′‐ethano‐D‐ribonucleosides 1–8 (= (5′,8′‐dihydroxy‐2′‐oxabicyclo‐[3.3.0]oct‐3′‐yl)purines or ‐pyrimidines) of the nucleobases adenine, thymine, cytosine, and guanine. They differ from natural 2′‐deoxyribonucleosides only by an additional ethylene bridge between the centers C(3′) and C(5′). The configuration at these centers (3S,5′R) was chosen as to match the geometry of a repeating nucleoside unit in duplex DNA as close as possible. These nucleosides were designed to confer, as constituents of an oligonucleotide chain, a higher degree of preorganization of a single strand for duplex formation with respect to natural DNA, thus leading to an entropic advantage for the pairing process. The synthesis of these ‘bicyclonucleosides’ was achieved by construction of an enantiomerically pure carbohydrate precursor 18/19 (Schemes 1), which was then converted to the corresponding nucleosides by known methods in nucleoside synthesis (Schemes 2 and 3). In all cases, both anomeric forms of the nucleosides were obtained in pure crystalline form, the relative configuration of which was established by 1H‐NMR‐NOE spectroscopy. A conformational analysis of the nucleosides with β‐configuration at the anomeric center by means of X‐ray and 1H‐NMR (including NOE) spectroscopy show the furanose part of the molecules to adopt uniformly a 1′exo‐conformation with the base substituents preferentially in the anti‐range in the pyrimidine nucleosides (anti/syn ca. 2:1) distribution in the purine nucleosides (in solution).
C‐Alkylation of Sarcosine Residues in Cyclic Tetrapeptides via Lithium Enlates
Authors: Miller Scott A. , Griffiths Sian L. , Seebach Dieter 
Published: December 2004

AbstractThe cyclic tetrapeptides cyclo(‐Leu‐Sar‐Gly‐), cyclo(‐Val‐Sar‐Sar‐Gly‐), and cylco(‐Meleu‐Gly‐D‐Alasar‐) have been synthesized from the component amino acids (BOP‐Cl coupling), using the pentafluorophenyl esters for the cyclization step (42, 13, and 30% yield, respectively). Multiple deprotonation (LDA in THF/LiBr/DMPU) and addition of highly reactive electrophiles (CF3CO2D, MeI, CH2O, CH2CHCH2Br, PhCH2Br) produce cyclic tetrapeptides with additional substituents introduced diastereoselectively (70 to > 98% ds) in yields ranging from 20 to 90%. The C‐alkylatd products are all derived from a sarcosine‐enolate moiety adjacent to another N‐methylamino acid. The structures of the resulting products are determined by NMR spectroscopy (DNOE and ROESY techniques) and by hydrolysis to the parent amino acids, suitable derivatization, and analysis by chromatography on a chiral GC column. It was shown in two cases that the overall yield of cyclization/alkylation to give a disubstitued cyclic tetrapeptide is higher than that of a synthesis of the same product from the corresponding amino‐acid building blocks. Surprising temperature and salt effects on the yields and selectivities of the reactions of the cyclic tetrapeptide enolates are presented, and possible mechanistic interpretations are discussed.
Absolute Configuration of 2‐Substituted 2‐Azabicyclo[2.2.1]hept‐5‐enes
Authors: Pombo‐Villar Esteban , Boelsterli Jakob , Cid Maria Magdalena , France Julien , Fuchs Beat , Walkinshaw Malcolm , Weber Hans‐Peter 
Published: December 2004

AbstractThe diastereoisomeric 2‐substituted 2‐azabicyclo[2.2.1]hept‐5‐enes 2–4 were prepared by aza‐Diels‐Alder reaction of cyclopentadiene with the corresponding methaniminium ions. Their relative configurations were deduced using 1H, 1H‐ROESY experiments, and their absolute configurations were assigned from the crystal structure of the aziridinium derivative (−)‐5. The absolute configuration of (+)‐1, i.e. (1R), was assigned by CD spectroscopy.
Photoisomerization of 2H,6H‐thiin‐3‐one 1‐oxides to 3H,7H‐[1,2]oxathiepin‐4‐ones
Authors: Kowalewski Ronald , Margaretha Paul 
Published: December 2004

AbstractOxidation of 2H, 6H‐thiin‐3‐ones 1a–c with 3‐chloroperbenzoic acid affords the corresponding 1‐oxides 2a–c. On irradiation (350 nm) in either benzene or MeCN, these cyclic sulfoxides 2 isomerize to 3H, 7H‐1,2‐oxathiepin‐4‐ones 3. The tetramethyl derivative 3a is isolated by flash chromatography at −10°, but, at higher temperatures, it undergoes ring contraction and H2O elimination to give 4,4‐dimethyl‐2(2‐methylprop‐2enylidene)thietan‐3‐one (4). Diemthyloxathiepinones 3b and 3c undergo ring contraction in MeOH to afford 1‐(4‐methylthiophen‐2‐yl)ethanone (5) and two diastereoisomeric 4,4‐dimethyl‐2‐methoxy‐2‐(1‐methoxyethyl)thietan‐3‐ones (6 and 7, respectively).
Palladium‐Catalyzed ‘Metallo‐Ene’‐Type Cyclization/Vinylstannane Coupling of 1‐Acetoxy‐octa‐2,7‐dienes and 1‐Acetoxy‐oct‐2‐en‐7‐ynes
Authors: Oppolzer Wolfgang , Ruiz‐Montes José 
Published: December 2004

AbstractPalladiumbis(dibenzylideneacetone)/tri(2‐furyl)phosphine‐catalyzed cyclizations of dienyl acetates 2 in the presence of an (1‐alkenyl)(tributyl)stannane and ZnCl2 provided trans‐substituted 3‐alkenyl‐4‐vinylcyclopentanes 11 in good yields. Analogous intramolecular carbometallation/C,C‐coupling of enynyl acetates 4, 6, and 8 furnished, stereospecifically, monocylic trienes 19, 20, and 21, respectively.
Synthesis and Ruthenium‐Catalyzed Enantioselective Hydrogenation of 3‐O‐Substituted 1,3‐Dihydroxypropan‐2‐ones. Part 2
Authors: Cesarotti Edoardo , Antognazza Patrizia , Pallavicini Marco , Villa Luigi 
Published: December 2004

AbstractA number of 3‐O‐substituted 1,3‐dihydroxypropan‐2‐ones have been synthesized in view of their potential use as prochiral precursors of optically active glycerols. Indeed, the oxo‐ethers have been reduced to the corresponding 3‐O‐substituted glycerols via chiral Ru complexes derived from (S)‐binap, ( =(−)‐(S)‐2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthalene) with enantiomeric excesses up to 93%. The steric course of the catalytic reduction appears to be essentially dependent on the steric encumbrance of the substituents; indeed, a dramatic increase of the enantiomeric excess is observed when the bulky trityl group is substituted by the less encumbering benzyl or octadecyl groups.
Molecular Geometries by the Extended‐Hückel Molecular Orbital Method III: Band‐structure calculations
Authors: Brändle Martin , Calzaferri Gion 
Published: December 2004

AbstractGeometries of extended structures can be evaluated with the extended‐Hückel tight‐binding method by inclusion of a distance‐dependent weighted Wolfsberg‐Helmholz formula and an approximate two‐body electrostatic repulsive‐energy term. We explain the theoretical procedure which is shown to be straightforward. Application to (all‐trans)‐polyacetylene yields alternating C, C bond lengths and a bandgap of 1.6 eV at the optimized geometry, in good agreement with the experimental finding.