bluuebunny/crossref_metadata_2025 huggingface dataset:
The adamantane rearrangement of syn‐ and anti‐Tricyclo[4.2.1.1.12,5] decane. Part II. Rearrangements initiated by regioselective formation of carbocations at C(3) and C(9)
Authors: Brossi Marco , Ganter Camille
Published: December 2004

The endo‐ and exo‐alcohols 5–12 of syn‐(1) and anti‐tricyclo[4.2.1. 12.5]decane (2) were treated with BF3/Et3SiH (ionic hydrogenation) in order to study the behaviour of the corresponding regioselectively generated carbocations at C(3) (a (syn), b (anti)) and C(9) (c (syn), d (anti)). The anti‐hydrocarbon 2 is practically the sole product obtained starting with the four 3‐alcohols (via a→b from 5 and 6 (syn) and via b from 9 and 10 (anti)). The four 9‐alcohols in each case yield a mixture of 2‐endo, 3‐endo‐ (3) and 2‐exo,3‐exo‐trimethylene‐8,9,10‐trinorbornane (4) (via c → e from 7 and 8 (syn) and via d → f from 11 and 12 (anti)), but no hydrocarbon 2, i.e. none of the 1,3‐H shifts c → a and d → b is involved.
α‐Alkylierung von β‐Hydroxycarbonsäuren über 1,3‐Dioxan‐4‐on‐Enolate
Authors: Zimmermann Jürg , Seebach Dieter , Ha Tae‐Kyu
Published: December 2004

Highly Diastereoselective α‐Alkylation of β‐Hydroxycarboxylic Acids Through Lithium Enolates of 1,3‐Dioxan‐4‐ones

From serine, β‐hydroxyisobutyric acid (‘Roche’ acid) and β‐hydroxybutyric acid, the dioxanones 1–6 were prepared. The generation of the enolates of type I with LDA at −75° and alkylation gave products with trans‐configuration whereas protonation of the 5‐methyl‐substituted enolate allowed access to the cis‐configurated β‐hydroxybutyric‐acid derivative 12. Hydrolysis gave the free β‐hydroxy acids of ‘syn’‐and ‘anti’‐configuration. Alkylation of the 6‐unsubstituted dioxanones 1 and 3 yielded predominantly products resulting from attack in the cis‐position of the t‐Bu group. The ‘reactive’ conformation of the enolates involved is tentatively derived from the product configuration. The selectivity of the alkylation is also discussed in terms of the results of an ab‐initio calculation on the enolates M–P.
Stereoselectivity in Reactions of Metal Complexes. Part X. Kinetics and stereoselectivity of the inner‐sphere electron‐transfer reaction between [Co(bamap)H2O]+ (bamap = 2,6‐bis(3‐carboxy‐1,2‐dimethyl‐2‐azapropyl)pyridine) and optically active iron(II) complexes
Authors: Bernauer Klaus , Pousaz Philippe , Porret Joelle , Jeanguenat André
Published: December 2004

The kinetics of the electron‐transfer reaction between racemic or optically active [Co(bamap)H2O]+ and optically active Fe2+ complexes of the three new pentadentate ligands bamap, alamp, and valmp has been investigated. All the reacting species show C2 symmetry. With respect to aquo‐Fe2+, the reaction rate for the Fe2+ complexes is enhanced by a factor of 104 to 105, and the observed kΔΛ/kΛΛ ratio is 1.0, 1,9, and 1.2, respectively. In all cases where stereoselectivity is observed, the reaction is faster between the complexes of opposite absolute configuration (ΔΛ or ΛΔ) than between species with the same configuration (ΛΛ or ΔΔ). The stereoselectivity effects are discussed of the basis of the structure of the transition state and the interatomic distances between the two metal centers at the moment of electron transfer.
Synthesis of (+)‐1,3:2,5‐dianhydroviburnitol ((+)‐(1R,2R,3S,5R,6S)‐4,7‐dioxatricyclo[3.2.1.03,6]octan‐2‐ol)
Authors: Le Drian Claude , Vogel Pierre
Published: December 2004

Epoxidation of (−)‐(1R,2R,4R)‐2‐endo‐cyano‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐exo‐yl acetate ((−)‐5) followed by saponification afforded (+)‐(1R,4R,5R,6R)‐5,6‐exo‐epoxy‐7‐oxabicyclo[2.2.1]heptan‐2‐one ((+)‐7). Reduction of (+)‐7 with diisobutylaluminium hydride (DIBAH) gave (+)‐1,3:2,5‐dianhydroviburnitol ( = (+)‐(1R,2R,3S,4R,6S)‐4,7‐dioxatricyclo[3.2.1.03,6]octan‐2‐ol; (+)‐3). Hydride reductions of (±)‐7 were less exo‐face selective than reductions of bicyclo[2.2.1]heptan‐2‐one and its derivatives with NaBH4, AlH3, and LiAlH4 probably because of smaller steric hindrance to endo‐face hydride attack when C(5) and C(6) of the bicyclo‐[2.2.1]heptan‐2‐one are part of an exo oxirane ring.
Generic shapes for the conformation analysis of macrocyclic structures
Authors: Gerber Paul R. , Gubernator Klaus , Müller Klaus
Published: December 2004

A new algorithm for the systematic generation of conformations of macrocyclic systems is presented. The procedure is based on the concept of generic shapes that are found in such structures. These shapes are characterized by a selection of harmonics which occur in an approximate Fourier representation of the atomic coordinates of the rings. Following a fixed protocol, a limited set of in‐plane and out‐of‐plane circular harmonics is used to define an ensemble of generic ring shapes. These generic shapes are used as start structures for energy minimizations by a given force‐field method. To account for the possibility of having several final conformations originating from the same generic shape, the corresponding initial structure is taken several times and subjected to a randomization step before minimization. The resulting conformations that fall within a preset low‐energy band are collected and screened for duplicates and enantiomers. The efficiency of this procedure (ratio between the number of accepted conformations and the total number of energy minimizations) depends on the flexibility of the macrocyclic system. The efficiency is generally quite high for very flexible rings. According to the proposed protocol, the number of generic shapes used as start structures grows as the square of N(lnN), where N is the ring size. The algorithm lends itself to conformational analyses of medium‐size and large rings as well as of loops spanned between fixed structural units.
Synthesis and Characterization of DNA Fragments Bearing an Adenine Radiation Product: 7,8‐Dihydroadenin‐8‐one
Authors: Guy André , Duplaa Anne‐Marie , Harel Philippe , Téoule Robert
Published: December 2004

The 7,8‐dihydroadenin‐8‐one is one of the base derivatives formed by the action of ionizing radiation upon DNA. In order in investigate the mutagenic effects and the repair of DNA lesions induced by gamma rays, the synthesis of oligonucleotides bearing this damage has been performed by the phosphoramidite methodology. The preparation of the corresponding protected mononucleotide 6 (see Scheme) and its insertion into a DNA fragment are described. The modified oligonucleotide was purified by HPLC, characterized by DNA sequencing, enzymatic hydrolysis, and FAB mass spectrometry. In the experimental conditions used herein, no basic or acidic degradation was observed. In the DNA chain, the lesion is stable on piperidine heating under the usual DNA sequencing conditions.
Mammalian Alkaloids: O‐methylation of (S)‐ and (R)‐dideoxynorlaudanosoline‐1‐carboxylic acid by catechol O‐methyltransferase and identification of a yellow pigment obtained at physiological pH
Authors: Rozwadowska Maria Danuta , Chrzanowska Maria , Brossi Arnold , Creveling Cyrus R. , Bembenek Michael E. , Abell Creed W.
Published: December 2004

O‐Methylation of optically active 3′,4′‐dideoxynorlaudanosoline‐l‐carboxylic acids 1 with O‐methyltransferase in vitro afforded almost exclusively the 7‐O‐methylated acids 3. A similar result was obtained with the yellow quinonemethide 4A obtained from 1 at neutral or slightly alkaline pH by oxidative decarboxylation and affording the 3,4‐dihydroisoquinoline 15 on methylation with catechol O‐methyltransferase (COMT). The structure of quinonemethide 4A was determined on the basis of spectral data, by its conversion into isoquinolines of established structure, and by synthesis. Quinonemethide 4A was found to be a weak inhibitor of monoamine oxidase A (MAO A) but not a substrate. Nonenzymatic oxidative decarboxylation of dopamine‐derived tetrahydroisoquinoline‐l‐carboxylic acids to quinonemethides may be a major factor in biochemical experimentation and should be considered in the interpretation of data.
Synthesis, Structure Elucidation, and Pharmacological Evaluation of 5‐Methyl‐oxymorphone (= 4,5α‐epoxy‐3,14‐dihydroxy‐5,17‐dimethylmorphinan‐6‐one)
Authors: Schmidhammer Helmut , Deeter Jack B. , Jones Noel D. , Leander J. David , Schoepp Darryle D. , Swartzendruber John K.
Published: December 2004

Synthesis of 5‐methyl‐oxymorphone (3) was accomplished by oxidation of 5‐methylthebaine (4) with performic acid, followed by catalytic hydrogenation and cleavage of the 3‐MeO group. X‐Ray analysis confirmed that the 14‐OH group has, like the one in oxymorphone (1), β‐orientation. Pharmacological studies in vivo and in vitro showed 3 to possess slightly less opioid agonistic properties than 1.
Energy‐Minimized Structures and Calculated and Experimental Isomer Distributions in the Hexaaminecobalt(III) system [Co(trap)2]3+ (trap = 1,2,3‐propanetriamine)
Authors: Comba Peter , Hambley Trevor W. , Zipper Luc
Published: December 2004

The two isomers of [Co(trap)2]3+ (meso‐[Co(trap)2]3+ and rac‐[Co(trap)2]3+; trap = 1,2,3‐propanetriamine) have been studied by strain‐energy minimization. The two isomers have been separated preparatively by fractional crystallization, and fully characterized by 13C‐NMR and electronic spectroscopy, and microanalyses. The calculated isomer distribution (rac/meso = 60%: 40%) is in good agreement with HPLC analysis of thermodynamic equilibrium mixtures at 298 K and 353 K (rac/meso = 55% : 45%). These results are discussed in relation to the approach of calculating isomer distributions of hexaaminecobalt(III) systems by strain‐energy minimization neglecting the differences in environmental effects.
Sphinxolide, a 26‐Membered Antitumoral Macrolide Isolated from an Unidentified Pacific Nudibranch
Authors: Guella Graziano , Mancini Ines , Chiasera Giuseppe , Pietra Francesco
Published: December 2004

It is shown that an unidentified nudibranch of Hawaiian waters contains a 26‐membered macrolide, sphinxolide ((−)‐1) with potent activity against the KB cell line. The structure of sphinxolide, a 2:1 mixture of (E/Z)‐isomers at the formamide moiety, is established to be (–)‐1 on the basis of extensive NMR and FAB‐MS analysis, in combination with data for the products of mono‐ (→(−)‐2) and diacetylation (→(+)‐3).
Total Synthesis of L‐Allose, L‐Talose, and derivatives.
Authors: Auberson Yves , Vogel Pierre
Published: December 2004

(1S, 4R, 5S, 6S)‐5‐exo, 6‐exo‐(Isopropylidenedioxy)‐7‐oxabicyclo[2.2.1]heptan‐2‐one ((−)‐1) was transformed with high stereoselectivity to L‐allose. Similarly, enantiomer (+)‐1 was transformed into L‐talose. The ketones (+)‐1 and (−)‐1 were derived from furan and 1‐cyanovinyl (1S)‐camphanate and 1‐cyanovinyl (1R)‐camphanate, respectively.
Eine neue Azepinring‐Synthese
Authors: Kvita Vratislav , Sauter Hanspeter , Rihs Grety
Published: December 2004

A New Azepine‐Ring Synthesis

A new one‐step synthesis of an azepine ring is described. The 2H‐pyran‐2‐one ring of methyl cumalate (8) or cumalaldehyde (2) upon reaction with an 1‐aminoacryl derivative, e.g. 1 or 6, is opened with subsequent decarboxylation to give a 1‐aminobutadiene derivative that undergoes an electrocyclic ring closure to the azepine ring (Schemes 1 and 2).
Direct Formation of a Substituted [5.5.5.5]Fenestrane by Intramolecular Arene‐Olefin Photocycloaddition
Authors: Mani Jürg , Schüttel Stefan , Zhang Cong , Bigler Peter , Müller Christian , Keese Reinhart
Published: December 2004

In a search for further synthetic routes to substituted [5.5.5.5] fenestranes, compound 1a, a derivative of 7‐methoxyindane, was photolyzed. Two of the three photoproducts, viz. the [3.5.5.5]fenestrane 3a and the isomer 4a, are formed according to the expected intramolecular meta‐cycloaddition. A different mechanism is suggested for the formation of the major component 2a.
Syntheses of Bile Pigments. Part 16. Synthesis of a vinyl‐substituted 2,3‐Dihydrobilinedione: Possible role of this new class of bile pigments in phycobilin biosynthesis
Authors: Gossauer Albert , Nydegger Fredy , Benedikt Eva , Köst Hans‐Peter
Published: December 2004

The total synthesis of racemic cis‐2,3,181, 182, ‐tetrahydroprotobiliverdin IXα dimethyl ester (19b), which is identical with the dimethyl ester of rac‐4, is described (Scheme 2). Under virtually neutral conditions, in solution, this bile pigment isomerized within a few min to racemic Z‐phycocyanobilin dimethyl ester (rac‐5b). Likewise, acid‐catalyzed allyl rearrangement of 3‐vinyl‐substituted cis‐ and trans‐2,3‐dihydrodipyrrin‐1(10H)‐ones 11c and 13c, respectively, yielded the corresponding ethylidene derivatives. In this case, however, the E‐isomer was formed stereo selectively from both substrates. The above results prove that, if protobiliverdin IXα (2) is transformed enzymatically to its 2,3,181, 182‐tetrahydro derivative, the latter would isomerize spontaneously to phycocyanobi‐lin. The biosynthesis of bacteriochlorophyll a and b from a common precursor bearing a vinyl group at C(8)may be straightforwardly explained in the same way.
Ferroelectric Liquid Crystals. Part 9. Laterally substituted phenyl benzoates incorporating a trans‐1,4‐disubstituted cyclohexane ring
Authors: Kelly Stephen M.
Published: December 2004

About 65 diverse phenyl benzoates incorporating a trans‐1,4‐disubstituted cyclohexane ring and at least one lateral substituent have been synthesised. The dependence of the liquid‐crystal transition temperatures of these materials on various lateral substituents (F, Cl, CN, and Br) in different positions of the esters has been investigated systematically. The influence of up to four F‐atoms in various positions of a standard ester has been thoroughly studied and the optimum combination for a broad smectic C mesomorphic range established. In consequence, three homologous series incorporating the 4‐alkoxy‐2,3‐difluorobenzoic‐acid moiety were prepared. An additional CC bond was introduced into the alkyl chain attached to the cyclohexane ring of some of these esters and the resulting modifications of the transition temperatures determined. Three ester series incorporating a lateral substituent and the optically active (+)‐(S)‐(1‐methylheptyl)oxy substituent have also been synthesised, and similar effects have been observed. These materials can be used as important components of commercial chiral smectic C mixtures for electro‐optic display device applications.
A Novel Access to Ionone‐Type Compounds: (E)‐4‐oxo‐β‐ionone and (E)Oxo‐β‐irone via metal‐catalyzed intramolecular reactions of α‐diazo ketones with furans
Authors: Wenkert Ernest , Decorzant René , Näf Ferdinand
Published: December 2004

(E)‐5‐Demethyl‐4‐oxo‐β‐ionone (2), (E)‐4‐oxo‐β‐ionone (3), (E)‐4‐oxo‐β‐irone (4), and the five‐membered ring analogs 36–41 were synthesized by a novel, convergent route starting from 2‐methylfuran (1). A recently discovered, intramolecular reaction of 2‐(diazoacyl)furans, catalyzed by dirhodium tetraacetate, leading to dienediones served as key step, thereby testing its utility in natural‐product synthesis for the first time.
Halochrome Molekeln 8. Mitteilung. Synthese und acidobasisches Verhalten von 3′‐substituierten 6,11‐Dihydrospiro[[1]benzopyrano[4,3‐b]indol‐6,9′−9′H‐xanthenen]
Authors: Gunzenhauser Sigmund , Balli Heinz
Published: December 2004

Halochromic Molecules. Synthesis and Acidobasic Properties of 3′‐substituted 6,11‐dihydrospiro[[1]benzopyrano[4,3‐b]indol‐6,9′−9′9′H‐xanthenes]

We have synthesized a series of 3′‐substituted 6,11‐ihydrospiro[6H‐chromeno[4,3‐b]indol–6,9′−9′H‐xanthenes] and one of their respective aza analogues. 1H‐MR data as well as the fragmentation in the mass spectra of starting and final products supported the postulated structures. With acid, the spiro compounds form ring‐opened intensely coloured xanthylium salts. UV/VIS spectra of these salts are listed and discussed. The ϵpH* curves in buffered MeOH/H2O solutions and the pK* values are determined. The title compounds could possibly be used in ‘pressure sensitive papers’.
Synthese von {2‐[3‐(2‐Ammonioethoxy)benzoyl]ethyl}‐trimethylammonium‐Bromid‐hydrobromid für die Affinitätschromatographie von Cholin‐Acetyltransferase (ChAT; EC 2.3.1.6)
Authors: Riggio Gaetano , Josef Raeber Alexander , Herbert Hopff Wolfgang
Published: December 2004

Synthesis of {2‐[3‐(2‐Amonioethoxy)benzoyl]ethyl}trimethylammonium Bromide Hydrobromide for the Affinity Chromatography of Choline Acetyltransferase (ChAT; EC 2.3.1.6)

ChAT is an essential enzyme that catalyzes the synthesis of acetylcholine from choline and activated acetic acid. For the affinity chromatography or biospecific adsorption, only those ligands are suited, which resemble the natural substrate. The ligands, however, cannot be bound directly to the matrix, but must be separated by a covalently bound spacer. Contrary to the often cited desorption by ionic gradients, we used the most specific desorption by the same ligand. The synthesis comprises seven steps starting from 3‐hydroxyacetophenon (7).
New fluorinating reagents. Part II. Preparation and Synthetic Application of a Saccharin Derived N‐Fluorosultam
Authors: Differding Edmond , Lang Robert W.
Published: December 2004

The synthesis of the new saccharin derived N‐fluorosultam 1 is described. A comparative study with commercially available N‐fluorosulfonamides shows 1 to be a superior fluorinating reagent for the synthesis of α‐fluorocarbonyl compounds.
Herstellung substituierter 1,6‐Methano[10]annulene durch Cycloadditionsreaktionen des 1H‐Cyclopropabenzols
Authors: Neidlein Richard , Kohl Matthias , Kramer Walter
Published: December 2004

Synthesis of Substituted 1,6‐Methano[10]annulenes by Cycloadditions of 1H‐Cyclopropabenzene

Diels‐Alder reactions of 1H‐cyclopropabenzene (1) with electron‐poor dienes, leading to substituted 1,6‐methano[10]annulenes, are described.
Structure and Thermal Behaviour of Methylcyclopentadiene Dimers
Authors: Thommen Walter , Pamingle Hervé , Schulte‐Elte Karl H.
Published: December 2004

The mixture of isomeric dimethyl‐endo‐tricyclo[5.2.1.02,6]deca‐3,8‐dienes (A) resulting from Diels‐Alder reactions of 1‐, 2‐, and 5‐methylcyclopenta‐1,3‐dienes (i–iii, respectively) at 20° was shown by GLC analysis to consist of at least 10 components (Table 1). The structures of the six major isomers 1–6, representing 96% of the total mixture, were established by 1H‐ and 13C‐NMR spectroscopy. Whereas on heating up to 110° the proportions of 1, 2, 4, and 6 remain nearly unaffected (±2 %), the dimers 3 and 5, formed in 22 % and 24 % yield, respectively, at 20°, isomerise above 70° reversibly via [3,3]‐sigmatropic rearrangement and equilibrate at 110° to a ca. 10:1 ratio.
An Electrochemical Variant in the Syntheses of Exaltone® and muscone: Anodic fragmentation of α, β‐unsaturated tosylhydrazones
Authors: Limacher Liviana L. , D. Delay François , Bédert Nicole , Tissot Paul
Published: December 2004

Ring enlargement of bicyclo[10.3.0]pentadec‐1(12)‐en‐13‐one p‐toluenesulfonylhydrazone into cyclopentadec‐4‐yn‐l‐one was accomplished under mild and controlled anodic oxidation conditions. The mechanism of this fragmentation is reconsidered.
Tilcotil® Studies [3+2] additions with isothiazol‐3(2H)‐one 1,1‐dioxide
Authors: Burri Kaspar F.
Published: December 2004

Derivatives of isothiazol‐3(2H)‐one 1,1‐dioxide react regiospecifically with 1,3‐dipolar agents. The main regiocontrolling factor is ascertained to be the CO group of the dipolarophile. The topology of the adducts is also in general agreement with predictions based on perturbation theory. Several adducts can be aromatized to heterocyclic equivalents of saccharin, and may then be elaborated into structural analogs of tenoxicam (Tilcotil® and piroxicam (Feldene®)).
Synthesis of 8‐Aza‐2′‐deoxyadenosine and related 7‐Amino‐3H‐1,2,3‐triazolo[4,5‐d]pyrimidine 2′‐Deoxyribofuranosides: Stereoselective glycosylation via the nucleobase anion
Authors: Kazimierczuk Zygmunt , Binding Uwe , Seela Frank
Published: December 2004

The synthesis of 8‐aza‐2′‐deoxyadenosine ( = 7‐amino‐3H‐1,2,3 triazolo[4,5‐d]pyrimidine N3‐(2′‐deoxy‐β‐D‐ribofuranoside); 1) as well as the N2‐ and N1‐(2′‐deoxy‐β‐D‐ribofuranosides) 2 and 3 is described. Glycosylation of the anion of 7‐amino‐3H‐1,2,3‐triazolo[4,5‐d]pyrimidine (6) in DMF yielded three regioisomeric protected 2′‐deoxy‐β‐D‐ribofuranosides, i.e. the N3‐, N2‐, and N4‐glycosylated isomers 7 (14%), 9 (11%), and 11 (3%), respectively, together with nearly equal amounts of their α‐D‐anomers 8 (13%), 10 (12%), and 12 (4%; Scheme 1). The reaction became Stereoselective for the β‐D‐nucleosides if the anion of 7‐methoxy‐3H‐1,2,3‐triazolo[4,5‐d]pyrimidine (13) was glycosylated in MeCN: only the N3‐, N2, and N1‐(2′‐deoxy‐β‐D‐nucleosides) 14 (29%), 15 (32%), and 16 (23%), respectively, were formed (Scheme 2). NH3 Treatment of the methoxynucleosides 14–16 afforded the aminonucleosides 1–3. The anomeric configuration as well as the position of glycosylation were determined by combination of 13C‐NMR, 1H‐NMR, and 1D‐NOE difference spectroscopy. Compound 1 proved to be a substrate for adenosine deaminase, whereas the regioisomers 2 and 3 were not deaminated.
Novel cembranolides (Coralloidolide D and E) and a 3,7‐Cyclized cembranolide (Coralloidolide C) from the mediterranean coral Alcyonium coralloides
Authors: D'Ambrosio Michele , Guerriero Antonio , Pietra Francesco
Published: December 2004

The Mediterranean alcyonacean Alcyonium (= Parerytkropodium) coralhides (PALLAS, 1766) is shown to contain three novel diterpenes which are of biogenetic significance: the 3,7‐cyclized cembranoid Coralloidolide C ( = (+)‐(6R*, 7R*, 11S*, 12aS* 3aE)‐7,8‐epoxy‐3,5,6,7,8,9,10,11,12,12a‐decahydro‐12a‐hydroxy‐11‐isopropenyl‐1,4‐dimethyl‐3‐oxocyciopentacydoundecene‐8,6‐carbolactone; (−)‐3), the O‐bridged diketonic cembranolide Coralloidolide D (= (+)‐(1R*, 2S*, 3R*, 5R*, 12S*, 8Z)‐2,5‐epoxy‐1‐hydroxy‐12‐isopropenyl‐5,9‐dimethyl‐7,10‐dioxocyclotetradeca‐8‐ene‐1,3‐carbolactone; (+)‐4), and the diketonic epoxycembranolide coralloidolide E (=(+)‐(1R*, 2R*, 3R*, 12S*, 5Z, 8Z)‐1,2‐epoxy‐12‐isopropenyl‐5,9‐dimethyl‐7,10‐dioxocyclotetra‐deca‐5,8‐diene‐1,3‐carbolactone; (+)‐5), The latter in pyridine at r. t. undergoes a double bond shift from C(4) = C(5) to C(4) = C(18) to give the isomer (−)‐7. Structural assignments are mainly based on ID and 2D NMR and MS spectral data. Either corailoidolide A ((−)‐1) or the hypothetic unsaturated 1,4‐diketone 9 can be envisaged as the precursors of all coralloidolides.
Nucleotides. Part XXXI. Modified Oligomeric 2′–5′ A Analogues: Synthesis of 2′–5′ oligonucleotides with 9‐(3′‐azido‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine and 9‐(3′‐amino‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine as modified nucleosides
Authors: Herdewijn Piet , Charubala Ramamurthy , Pfleiderer Wolfgang
Published: December 2004

A series of new 2′–5′ oligonucleotides carrying the 9‐(3′‐azido‐3′deoxy‐β‐D‐xylofuranosyl)adenine moiety as a building block has been synthesized via the phosphotriester method. The use of the 2‐(4‐nitrophenyl)ethyl (npe) and 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) blocking groups for phosphate, amino, and hydroxy protection guaranteed straightforward syntheses in high yields and easy deblocking lo form the 2′–5′ trimers 21, 22, and 25 and the tetramer 23. Catalytic reduction of the azido groups in [9‐(3′‐azido‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine]2′‐yl‐[2′‐(Op‐ammonio)→ 5′]‐[9‐(3′‐azido‐3′‐deoxy‐β‐D‐xylofuranosyl)adenin]‐2′‐yl‐[2′‐(Op‐ammonio)→ 5′]‐9‐(3′‐azido‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine (21) led to the corresponding 9‐(3′‐amino‐3′‐deoxy‐β‐D‐xylofuranosyl)‐adenine 2′–5′ trimer 26 in which the two internucleotidic linkages are formally neutralized by intramolecular betaine formation.
Tordanone, un stéroïde replié avec une jonction de cycle A/B β‐cis (5β) et B/C α‐cis(8α)
Authors: Haag Thierry , Hetru Charles , Luu Bang
Published: December 2004

Tordanone, a Twice Bent Steroid Structure with Ring A/B β‐cis(5β)‐ and Ring B/C α‐cis(8α)‐Fused

The 3β, 14α, 25‐trihydroxy‐5β, 8α‐cholestan‐6‐one ( = tordanone; 4) has been prepared by stereospecific hydrogenation of 3β, 14α, 25‐trihydroxy‐5β‐cholesta‐7,22ξ‐dien‐6‐one (5). This is the first stereospecific synthesis of a B/C cis‐fused steroid belonging to the 5β, 8α ‐cholestane group with a H‐atom at positions 5β (A/B cis‐fused) and 8α. The resulting twice bent structure shows a particularly strong steric hindrance of the β‐face where CH3(18) at the C/D ring junction and HβC(7) of the B ring are very close to each other. Structural features and mechanistic aspects of the hydrogenation are discussed.
Total synthesis of 2‐(β‐D‐ribofuranosyl)thiazole‐4‐carboxamide (Tiazofurin) and of precursors of ribo‐C‐nucleosides
Authors: Bimwala R. Mampuya , Vogel Pierre
Published: December 2004

(1R,2S,4R)‐2‐Cyano‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐yl (1S′)‐camphanate (5) was transformed into (−)‐methyl 2,5‐anhydro‐3,4,6‐O‐tris[(tert‐butyl)dimethylsilyl]‐D‐allonate (2), (+)‐1,3‐diphenyl‐2‐{2′,3′,5′‐O‐tris[(tert‐butyl)dimethylsilyl]‐β‐D‐ribofuranosyl}imidazolidine (3), and the benzamide 20 of 1‐amino‐2,5‐anhydro‐1‐deoxy‐3,4,6‐O‐tris‐[((tert‐butyl)dimethylsily)]‐D‐allitol. Compound 2 was converted efficiently into optically active tiazofurin (1).
The stereoselectivity of the alkylation of the dianion of ethyl 2‐hydroxy‐6‐methylcyclohexanecarboxylates: Control of stereochemistry at three adjacent stereogenic centers
Authors: Fráter Georg , Günther Wulf , Müller Urs
Published: December 2004

Yeast reduction of rac‐ethyl 2‐methyl‐6‐oxocylohexanecarboxylate (rac‐1) yielded selectively (+)‐ethyl 2‐hydroxy‐6‐methylcyclohexane carboxylate (+)‐2 (Scheme 1) which has been alkylated with 5‐iodo‐2‐methylbut‐2‐ene by (the dianion method to furnish the 4‐methylbut‐3‐enyl derivat 3 (Scheme 3)). NaBH4 reduction of (+)‐1 led to three hydroxy‐carboxylates (−)‐2, (+)‐5, and (−)‐6 (Scheme 4). Allylation of the dianion of (+)‐5 afforded (+)‐7.
Mammalian Alkaloids: O‐Methylation of (±)‐Norcoclaurine‐1‐carboxylic Acid and Related Isoquinolines Including (S)‐ and (R)‐Norcoclaurine with 14C‐Labeled S‐Adenosyl‐L‐Methionine in Presence of Mammalian Catechol O‐Methyltransferase
Authors: Sekine Yasuo , Crevelling Cyrns , Bell Maureen , Brossi Arnold
Published: December 2004

(±)‐Norcoclaurine‐1‐carboxylic acid (5) and the derived dihydroisoquinolinone 6 (present as quinonemethide 6a at pH 7) afforded, on methylation with 14C‐labeled S‐adenosyl‐L‐methionine in the presence of mammalian catechol O‐methyltransferase, exclusively the 7‐O‐methylated congeners 7 and 9, respectively. High stereoselectivity of the O‐methylation was observed with (−)‐(S)‐ and (+)‐(R)‐norcoclaurine (2a and 2b, resp.), affording 80% of 6‐O‐methylated isoquinoline 12 and 20% of the 7‐O‐methylated isomer 11 from 2a, and the reversed proportion of 12 and 11 from 2b. Synthesis of the reference amino acid 8 was achieved by Pictet‐Spengler condensation of O‐benzyl‐protected dopamine 17 with benzyl‐protected keto acid 20 (→ 21) followed by methylation with diazomethane (→22 + 23) and removal of the protecting groups by acid hydrolysis. It is considered unlikely that amino acids such as 5 constitute important precursors in the biosynthesis of isoquinolines related to reticuline.
A Theoretical Investigation of Enantioselectivity: Michael Reaction of Secondary Enamines with Enones
Authors: Sevin Alain , Masure Daniel , Giessner‐Prettre Claude , Pfau Michel
Published: December 2004

A theoretical study of the enantioselective Michael‐type addition of chiral secondary enamines to enones has been achieved. In a first step, the structures of various free enamines have been investigated at the ab initio and MNDO levels. The results clearly show that upon substitution of the prototype vinylamine, the N‐center is pyramidalized. The study of enamines with chiral N‐substituents such as (S)‐Ph(Me)CH or (S)‐cyclohexyl(Me)CH reveals a very complex pattern, where up to 8 local energy minimums are characterized whose examination shows that no prediction can be. done regarding the final enantioselectivity of their reaction with enones. These sets of conformers can be regarded as nearly energetically degenerate, at least for the three or four ones of lowest energy. The study of the compact complexes formed between the latter optimal conformers and acrylaldehyde shows that: (i)syn complexation with respect to the N lone pair is the only one which remains possible for steric reason, (ii) small geometrical rearrangements take place as the complexation proceeds, (iii) no clear‐cut correspondence exists between the relative sequence of the low‐energy conformers of the free enamines and the sequence of the low‐energy complexes, (iv) the examination of the relative gradients of the complexation energies provides an index for predicting the relative facilities of the enantiometric pathways, in good agreement with the experimental facts. Our study emphasizes the great complexity of systems of realistic size and brings about critical conclusions regarding classical ad hoc models.
A novel glyceryl ester (glyceryl dendryphiellate A), a trinor‐eremophilane (dendryphiellin A1), and eremophilanes (dendryphiellin E1 and E2) from the marine deuteromycete Dendryphiella salina (SUTHERLAND) PUGHet NICOT
Authors: Guerriero Antonio , Cuomo Vincenzo , Vanzanella Fortunato , Pietra Francesco
Published: December 2004

Continuing studies of the global extracts from cultures of the marine deuteromycete Dendryphiella salina have led to the isolation of novel compounds that add to the scarce list of marine fungal metabolites. Besides (22E)‐ergosta‐4.6,8(14),22‐tetraen‐3‐one which, though known from basidiomycetes, was unknown in the sea, they are an unusual glyceryl ester, i.e. glycer‐1‐yl dendryphiellale A (= (+)‐(2R)‐2,3‐dihydroxyprop‐l‐yl (6S,2E,4E)6‐methylocta‐2,4‐dienoate; (+)‐1), a trinor‐eremophilane, i.e. dendryphiellin A1 ( = (+)‐(3R*,4E,6E)‐7‐{[(1R*,2S*,7R*,8aR*)‐1,2,6,7,8,8a‐hexahydro‐7‐hydroxy‐1,8a‐dimethyl‐6‐oxonaphthalen‐2yl]oxycarbonyl}‐3‐methylhepta‐4,6‐dienoic acid; (+)‐11), and two eremophilanes, i.e. dendryphiellin El ( = (+)‐(1R*, 2S*, 7S*,8aR*)‐1,2,6,7,8,8a‐hexahydro‐1,8a‐dimethyl‐7‐(1‐methylethenyl)‐6‐oxonaphthalen‐2‐yl(6S,2E,4E)‐6‐methyl‐octa‐2,4‐dienoate; (+)‐13) and dendryphiellin E2 ( = (+)‐(1R*, 2S*, 8aR*)‐1,2,6,7,8,8a‐hexahydro‐7‐isopropyl‐idene‐1,8a‐dimethyl‐6‐oxonaphthalen‐2‐yl (6S,2E,4E)‐6‐Methylocta‐2,4‐dienoate; (+)‐14). Absolute configurations have been established for (+)‐1 via total synthesis and for the acid portion of (+)‐13 and (+)‐14 via transesterification in NaOMe/MeOH which gave in both cases melhyl dendryphiellate A ((+)‐16) of known configuration and the free alcoholic moiety of (+)‐14, i.e. (+)‐17.
Synthesis of 24‐Methylidene[24‐14C]‐ and 24‐Methylidene[7‐3H]cholesterol
Authors: Monteagudo Edith S. , Burton Gerardo , Gros Eduardo G.
Published: December 2004

The syntheses of 24‐methylidene[24‐14C]cholesterol (7a) and of 24‐methylidene[7‐3H]cholesterol (7b) from commercially available (20S)‐3‐oxopregn‐4‐ene‐20‐carbaldehyde (1) are described. The method also provides simple preparations of 3β‐acetoxy[24‐14C]chol‐5‐en‐24‐oic acid (4) and 24‐oxocholest‐5‐en‐3β‐yl acetate (6b).
Stereoselektive Synthesen von substituierten Tricarbonyl[tris(methylen)methan]eisen(0)‐Komplexen
Authors: Kappes Dag , Gerlach Hans , Zbinden Peter , Dobler Max
Published: December 2004

Stereoselective Syntheses of Substituted Tricarbonyl[tris(methylen)methan]iron(0) Complexes

The complexes 3, 9, 10, 22, and 23 with one, two, and three Me substituents at the tris(methylen)methane moiety have been synthesized from the (acyloxy‐1,3‐diene)(tricarbonyl)iron(0) complexes 1, 4, 5, 20, and 21, respectively, by ionic hydrogenation with BF3 and Et3SiH at −78° in CH2C12. These reductions are completely stereoselective, and their course can be predicted by assuming a dominant stereoelectronic control of the reaction. Formation of the carbocationic intermediates 11 from 4 and 12 from 5, e.g., takes place only if the dissociating OC bond is antiperiplanar to the donor C(β)Fe bond. Fast H‐transfer then converts the intermediate 11 to 9 and 12 to 10. The configurations of 17 and 20 can be deduced from the structure of 22 and those of 18 and 21 from that of 23. An X‐ray structure determination of (1R,4S)camphanoate (−)‐13 derived from alcohol (−)‐7 confirms the configuration of 5 deduced above, The structures of the complexes 9 and 10, 22 and 23 were determined by their unique NMR spectra. The diastereoisomeric complexes 6 and 7 have been synthesized from aldehyde 8 with MeMgI, the diastereoisomers 17 and 18 analogously from 16 or from methyl ketone 19 by reduction with LiAlH4. Optically active starting materials (+)‐1, (−)‐13, (+)‐20, and (+)‐21 gave, by ionic hydrogenation, the complexes (−)‐(3R)‐3, (+)‐(2S,4S)‐10, (−)‐(R,R, S)‐22, and (−)‐(R,R,R)‐23 respectively, with known absolute configurations.
1‐Methoxycarbonyl‐substituiertes 2,3‐Dihydropyridin‐4(1H)‐on (= Methyl‐1,2,3,4‐tetrahydro‐4‐oxopyridin‐1‐carboxylat) als Chromophor für die photochemische [2 + 2]‐Cycloaddition
Authors: Guerry Philippe , Blanco Philippe , Brodbeck Heinz , Pasteris Olivier , Neier Reinhard
Published: December 2004

1‐Methoxycarbonyl‐Substituted 2,3‐Dihydropyridin‐4(1H)‐one(= Methyl 1,2,3,4‐Tetrahydro‐4‐oxopyridine‐1‐carboxylate) as Chromophore for Photochemical [2 + 2]‐Cycloadditions

With olefins having an electron‐acceptor as well as with olefins having an electron‐donor substituent, 1‐methoxycarbonyl‐substituted dihydropyridinone 12 undergoes [2 + 2] cycloaddition in good preparative yields. The photochemical cycloaddition is highly regioselective. For preparative purposes, the ring junction can be equilibrated to the thermodynamically more stable cis‐junction. Only the ‘endo’/‘exo’ selectivity at the C‐atom bearing the olefin substituent cannot be controlled. The photodimerization of 12 is the only side reaction. Using a slight excess of the olefin, the photodimerization can be suppressed. The protecting group at the N‐atom of the dihydropyridinone can be varied in order to introduce an internal sensitizer, as shown with 1‐acyl‐substituted compound 29, which underwent the cycloaddition process even with sunlight.
Structure cristalline d'une thiazolorifamycine: rifamycine P
Authors: Léger Jean‐Michel , Carpy Alain
Published: December 2004

Crystal Structure of a Thiazolorifamycine: Rifamycine P

The crystal structure of a natural thiazolorifamycin, rifamycin P, as an adduct with EtOH and H2O, has been determined by X‐ray crystallography by a combination of direct methods and Patterson techniques. Block‐diagonal least‐squares refinement using 5996 independent reflections and 1475 parameters led to an R factor of 0.092 (two independent molecules of rifamycin P). The middle part of the ansa chain, essential for activity against the bacterial DNA‐dependent RNA polymerase (DDRP) resembles that of active rifamycins. The four OH groups lie on the same side of the molecule and are almost in the same plane. Interatomic distances between the O‐atoms agree well with a spatial model derived from X‐ray studies, performed on semisynthetic active rifamycins.
Preparation of a Key Intermediate for the Synthesis of the (±)‐Pentalenolactone E Methyl Ester by Catalytic ‘Palladium‐Ene Cyclization’/Methoxycarbonylation
Authors: Oppolzer Wolfgang , Xu Jin‐Zhu , Stone Charles
Published: December 2004

Bicyclic alcohol (±)‐2, an advanced intermediate for the synthesis of the methyl ester 1 of pentalenolactone E, has been synthesized in nine operations starting from aldehyde 7. The key step 6 → 9 is a Pd‐catalyzed, tandem intramolecular alkyne allylation/carbonylation reaction.
Synthese von enantiomerenreinem Mimulaxanthin und seiner (9Z,9′Z)‐ und (15Z)‐Isomeren
Authors: Baumeler Andreas , Eugster Conrad Hans
Published: December 2004

Synthesis of Enantiomerically Pure Mimulaxanthin and of Its (9Z,9′Z)‐ and (15Z)Isomers

We present the details of a synthesis of optically active, enantiomerically pure stereoisomers of mimulaxanthin (=(3s,5R,6R,3′S,5′R,6′R)‐6,7,6′,7′‐tetradehydro‐5,6,5′,6′‐tetrahydro‐β,β‐carotin‐3,5,3′,5′‐tetrol) either as free alcohols 1a and 24a or as their crystalline (t‐Bu)Me2Si ethers 1b and 24b. Grasshopper ketone 2a, a presumed synthon, unexpectedly showed a very sluggish reaction with Wittig‐Horner reagents. Upon heating with the ylide of ester phosphonates, an addition across the allenic bond occurred. On the contrary, a slow but normal 1,2‐addition took place with the ylide from (cyanomethyl)phosphonate but, unexpectedly, with concomitant inversion at the chiral axis. So a mixture of(6R,6S,9E,9Z)‐isomers 6–9 was produced {(Scheme 1). However, a fast and very clean 1,2‐addition occurred with the ethynyl ketone 12 to yield the esters 13 and 14 (Scheme 2). DIBAH reduction of the separated stereoisomers gave the allenic alcohols 15 and 16 in high yield. Mild oxidation to the aldehydes 17 and 18 followed by their condensation with the acetylenic C10‐bis‐ylide 19 led to the stereoisomeric 15,15′‐didehydromimulaxanthins 20 and 22, respectively (Schemes 3 and 4). Mimulaxanthins 1 and 24 were prepared by partial hydrogenation of 20 and 22 followed by a thermal (Z/E)‐isomerization. As expected, the mimulaxanthins exhibit very weak CD curves, obviously caused by the allenic bond that insulates the chiral centers in the end group from the chromophor. On the contrary, some of the C15‐allenic synthons showed not only fairly strong CD effects but also a split CD curve which, in our interpretation, results from an exciton coupling between the allene and the C(9)C(10) bond. We postulate a rotation around the C(8)C(9) bond, presumably caused by an intramolecular H‐bond in 16 or by a dipol interaction between the polarized double bonds in 6, 7, 8, and 17.
Palladium‐Catalyzed Ene‐Type Cyclizations of Terpenoid 1,6‐Enynes
Authors: Knierzinger Andreas , Grieder Alfred , Schönholzer Peter
Published: December 2004

Palladium‐catalyzed ene‐type cyclizations of 1,6‐enynes 2 yield methylidene‐cyclopentane derivatives 3. Removal of protecting groups from 3 furnishes the diols 4 and 5, whose configurations were established by a combination of X‐ray and 1H‐NMR techniques. The predominant formation of isomers 4 is discussed in the context of two alternative hypothetical mechanisms previously proposed for this type of cyclization.
Syntheses of Pyrrolo[2,3‐d]pyrimidine 2′,3′‐Dideoxyribonucleosides Related to 2′,3′‐Dideoxyadenosine and 2′,3′‐Dideoxyguanosine and Inhibitory Activity of 5′‐Triphosphates on HIV‐1 Reverse Transcriptase
Authors: Seela Frank , Muth Heinz‐Peter , Röling Angelika
Published: December 2004

The synthesis of 4‐chloropyrroIo[2,3‐d]pyrimidine and 2‐amino‐4‐chloropyrrolo[2,3‐d]pyrimidine α‐D‐ and β‐D‐2′,3′‐dideoxyribonucleosides6a,band7a,bis described (Scheme 1). Glycosylation of the pyrrolo[2,3‐d]‐pyrimidinyl anions of1a,bwithin situprepared 2,3‐dideoxy‐α/β‐D‐glycero‐pentofuranosyl chloride (2) was regioselective but afforded anomeric mixtures of the 2′,3′‐dideoxyribonucleosides3a/4aand3b/4b, respectively. The glycosylation products were deprotected and subjected to nucleophilic displacement yielding various pyrrolo[2,3‐d]pyrimidine 2′,3′‐deoxyribonucleosides related to 2′,3′‐dideoxyadenosine and 2′,3′‐dideoxyguanosine. One‐pot phosphorylation gave the corresponding triphosphates. Some of them are strong inhibitors of HIV‐1 reverse transcriptase, similar to corresponding purine 2′,3′‐dideoxynucleotides, but exhibit a better selectivity index in comparison to DNA polymerases. According to that, the N(7) of the purine moiety is not an essential binding position of ddATP or ddGTP at the active centre of HIV‐1 reverse transcriptase.
1,7‐Dideaza‐2′,3′‐dideoxyadenosine: Syntheses of Pyrrolo[2,3‐b]pyndine 2′,3′‐Dideoxyribofuranosides and Participation of Purine N(1) during HIV‐1 Reverse Transcriptase Inhibition
Authors: Seela Frank , Gumbiowski Rainer
Published: December 2004

The syntheses of 1,7‐dideaza‐2′,3′‐dideoxyadenosine (1) and related pyrrolo[2,3‐b]pyridine 2′,3′‐dideoxyribi and 2′,3′‐didehydro‐2′,3′‐dideoxyribonucleosides (see 2–5) are described. As starting materials, 2′‐deoxyribo‐nucleosides 6 or 7 were used. The 3′‐OH group was removed by Barton deoxygenation or via mesylation follow by elimination and catalytic hydrogenation. Compound 1 was also obtained from the direct glycosylation of 4‐nitro‐1H‐pyrrolo[2,3‐b]pyridine (17) with the 2,3‐dideoxyribofuranosyl chloride 18. The triphosphate 25 of 1 showed only marginal activity against HIV‐1 reverse transcriptase, indicating that purine N(1) is required for the inhibitory activity of the parent 2′,3′‐dideoxyadenosine.
Zur Oxidation von 1,2‐Thiazolen: Ein einfacher Zugang zu 1,2‐Thiazol‐3(2H)‐on‐1,1‐dioxiden
Authors: Schulze Bärbel , Kirsten Gisela , Kirrbach Sabine , Rahm Annette , Heimgartner Heinz
Published: December 2004

Oxidation of 1,2‐Thiazoles; A Convenient Approach to 1,2‐Thiazol‐3(2H)‐one 1,1‐Dioxides

The 1,2‐thiazoles obtained from 3‐chloroalk‐2‐enals and ammonium thiocyanate (7 → 9, Scheme 1) are easily transformed to 1,2‐thiazol‐3(2H)‐one 1,1‐dioxidcs 10 on treatment with H2O2 in AcOH at 80°. Hydrogenation of 10 in AcOH yields the corresponding saturated 1,2‐thiazolidin‐3‐one 1,1‐dioxides 16 (Scheme 3). Cycloalka[c]‐1,2‐thiazoles 18 are prepared from 2‐[(thiocyanato)methyliden]cycloalkan‐1‐ones and ammonia (Scheme 4). Surprisingly, oxidation of 18a with H2O2 in AcOH yields the tricyclic oxaziridine 19.
Crystal Structures of the Lanthanum(III), Europium(III), and Terbium(III) Cryptates of Tris(bipyridine) Macrobicyclic Ligands
Authors: Bkouche‐Waksman Itka , Guilhem Jean , Pascard Claudine , Alpha Béatrice , Deschenaux Robert , Lehn Jean‐Marie
Published: December 2004

The crystal structures of the LaIII, EuIII, and TbIII complexes of macrobicyclic [bpy.bpy.bpy] ligands, [La3+ ⊂ 1]3 Cl− ( = 3‐La), [Tb3+ ⊂ 1]3 Cl− ( = 3‐Tb), and [Eu3+ ⊂ 2]3 C1− ( = 3‐Eu), have been determined. They confirm the cryptate nature of these species, the cations being bound to the eight N‐sites of the ligand. The macrobicycle presents two open faces, thus allowing additional coordination of two species, Cl− ions or H2O molecules, to the bound cations. These data provide structural support for the photophysical studies of the luminescent properties of the EuIII and TbIII cryptates, which indicated residual coordination of H2O molecules.
Site‐Selectivity in the Fe+‐Mediated CH/CC Bond Activation of Aldimines Short Communication
Authors: Prüsse Tilmann , Schwarz Helmut
Published: December 2004

It is demonstrated for the first time that the site‐selectivity for the Fe+‐mediated CH bond activation of aldimines R1NCHR2 (R1, R2 = alkyl) involves the alkyl chain R1 by a factor ≥ 12 in comparison to the alkenyl part R2. This finding explains previous observations that dehydrogenation of intermediates formed by alkene loss from either R1 or R2 of R1NCHR2/Fe+ preferentially involves the alkyl part.
Monosubstitution von Octa(hydridosilasesquioxan) H8Si8O12 zu R′H7Si8O12 mittels Hydrosilylierung Kurzmitteilung
Authors: Calzaferri Gion , Herren Daniel , Imhof Roman
Published: December 2004

Monosubstitution of Octa(hydridosilasesquioxane) H8Si8O12 to R′H7Si8O12 by Hydrosilylation

Hydrosilylation of hex‐1‐ene and of styrene by octa(hydridosilasesquioxanes) catalyzed by hexachloroplatinic acid leads to the first monosubstituted octasilasesquioxane R′H7Si8O12 molecules.
Metal complexes with macrocyclic ligands. Part XXXIV. Geometrical and conformational changes during the on/off reaction of the side chain in the CuII complex of 11‐(3‐aminopropyl)‐1,4,7,11‐tetraazacyclotetradecane
Authors: Schiegg André , Riesen Andreas , Kaden Thomas A.
Published: December 2004

Solution studies of the Cu2+ complex with 11‐(3‐aminopropyl)‐1,4,7,11‐tetraazacyclotetradecane(L) indicate that, depending on the pH and on the age of the solution, different species are present. Dissolving the solid [CuL](ClO4)2 in slightly acidic solution gives the protonated complex AH, characterized by an absorption maximum at 574 nm, by a relatively fast proton‐induced dissociation kinetics and by the typical colour change in basic solution to give the deprolonated form A with coordinated side chain. AH slowly interconverts in acidic solution to a new species BH, which has an absorption maximum at 547 nm, and which is kineticaily more stable against acid dissociation and shows no coordination of the amino group of the side chain. In alkaline solution, however, the deprotonated form B deliver A in a base induced reaction. The X‐ray diffraction studies of A and BH allow to determine the geometry of the metal ion and the configuration of the macrocycle. In A, the Cu2+ is pentacoordinated by the five N‐atoms of the ligand and the macrocycle is in the RRSR configuration, whereas in BH the Cu2+ is octahedrally coordinated by the four N‐atoms of the macrocycle and two axial perchlorate O‐atoms with the macrocycle in the RRRS configuration. The amino group of the side chain is protonated and not coordinated. Thus, the on/off equilibrium of the side chain not only changes the geometry of the metal ion, as is generally found, but also alters the macrocyclic moiety.
Unimolecular Gas‐Phase Oxidation of Terminal Hydroxy Groups in [FeO(CH2)nOH]+ Complexes (n = 2–8). A Case for OH Bond Activation by Late Transition‐Metal Ions. Preliminary Communication
Authors: Prüsse Tilmann , Schwarz Helmut
Published: December 2004

In contrast to Fe+/diol complexes, gas‐phase dehydrogenation of the corresponding FeII alkoxides, [FeO(CH2)nCH2OH]+, is a highly specific process in the course of which oxidation of the terminal OH group takes place. Based on labeling studies, this is the exclusive mechanism for n = 2 and 3 (Scheme: path ); for higher homologues, as for example [FeOf(CH2)7CH2OH]+, the labeling data demonstrate that an additional mechanism is operative, involving the dehydrogenation of internal positions of the alkyl chain (path ). The Fe+‐mediated oxidation –CH2OH → –CHO +H2: constitutes one of the rare examples of O‐H bond activation by late cationic transition‐metal ions.
Reaction of the 5‐Azoniafulvene Ion with Enamines: A New Approach to Pyrrolizines
Authors: Schärer Daniel , Jindra Vladimir , Bringhen Alain O. , Burger Ulrich
Published: December 2004

The synthesis of N,N‐dimethyl‐N‐[(pyrro‐1‐yl)methyl]anilinium chloride (14) and of the corresponding p‐toluidinium salt 15 is described. These salts, when dissolved in polar solvents, are shown to be in equilibrium with 1‐(chloromethyl)pyrrole (17) and thereby potentially with the 5‐azoniafulvene ion (2). Consequently, they react under very mild conditions (MeCN, 60°) with enamines to give pyrrolizine derivatives in acceptable yield (40–50°). The process is rationalized in terms of an initial Mannich‐type reaction which is immediately followed by acyclization.
A Molecular‐Mechanics Analysis of Complexes of the Sexidentate Macrocycles cis‐ and trans‐6,13‐Dimethyl‐1,4,8,11‐tetraazacyclotetradecane‐6,13‐diamine
Authors: Bernhardt Paul V. , Comba Peter
Published: December 2004

Molecular‐mechanics calculations of the sexidentate coordinated complexes of the pendant arm macrocyclic hexaamines trans‐ (L1) and cis‐6,13‐dimethyl‐3,4,8,11‐tetraazacyclotetradecane‐6,13‐diamine (L2) reveal that the trans‐isomer shows a preference toward small metal ions, whereas the L2 may coordinate a wider range of metal ions without significant intramolecular strain. Conformational disorder in previously reported crystal structures of complexes of L1 is interpreted, and predictions for some, as yet, unknown complexes of L2 are made.
Energy Transfer from a Lumazine (= Pteridine‐2,4(1H,3H)‐dione) Chromophore to Bathophcnanthroline‐ruthenium(II) Complexes during Hybridization Processes of DNA
Authors: Bamwarth Willi , Müller Francis
Published: December 2004

We incorporated 6,7‐dimethyllumazine chromophores and a [RuII(bathophenanthroline)] complex into different oligodeoxynucleotides, the former via the corresponding phosphoramidites of the 2′‐deoxynucleosides and the latter specifically by the phosphonate approach at the 5′‐end of synthetic oligonucleotides, directly in the course of their synthesis on solid support. Efficiency measurements of this energy‐transfer system with the lumazine as energy donor and the Ru complex as energy acceptor allowed us to distinguish between the hybridized and the non‐hybridized state of oligonucleotides. Thus, the approach should be of value in DNA probe technology for the detection of single‐stranded DNA targets.