bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and Highly Stereoselective Formation of 1:2 Metal‐to‐Ligand complexes with triamine 2,6‐bis(pyrolidin‐2‐yl)pyridine. meso‐[2,6‐bis(pyrrolidin‐2yl)pyridine]nickel(II) (meso‐[Ni(bpp)2]2+), a Metal Complex with S4 Symmetry
Authors: Bernauer Klaus , Gretillat François , Stoeckli‐Evans Helen , Warmuth Ruth 
Published: December 2004

AbstractThe X‐Ray structures of the 1:1 copper(II) complexes with racemic and opticall active (+)‐(R,R)‐(2,6‐bis(pyrrolidin‐2‐yl)pyridine ((+)‐bpp; (+)‐I) were determined. Whereas the perchlorate 1 of racemic complex contains the monomeric units with perfect C2 symmetry, the sulfate of the optically active compound crystallizes as a coordination polymer composed of sequences of three different five‐coordinate units linked by sulfate bridges around a threefold screw axis (see 2). Formation of the 1:2 complexes of nickel(II) with (±)‐bpp is shown to be highly stereoselective. Acidimetric titrations and CD measurements indicate that the equilibrium mixture contains 99% of the meso‐complex 3 belonging to the point group S4 and only 0.5% of each enantiomer of the C2‐symmetric optically active forms. The S4 symmetry of meso‐[Ni{(+)‐bpp}{(−)‐bpp}]ClO4)2 (3) was confirmed by X‐ray analysis. The formation of binary complexes of cobalt(II), zinc(II), and cadmium(II) with (±)‐bpp shows an excess of 28, 34, and 8%, respectively, of the meso‐form over the statistical amount. CD and UV/VIS measurement show a pH‐dependent high spin/low spin equilibrium between the octahedral [Ni(bpp)(H2O)3]2+ and the square‐planar [Ni(bpp)OH]+ in aqueous solution.
Vitamin‐B12‐Catalyzed C,C‐Bond Formation. Synthesis of a california red scale pheromone
Authors: Auer Lucas , Weymuth Christophe , Scheffold Rolf 
Published: December 2004

AbstractA Mixture of (3S,6R)‐ and (3R,6R)‐3‐methyl‐6‐(1‐methylethenyl)dec‐9‐enyl acetate (1a and 1b, respectively)–1a being a pheromone of the California red scale – is synthesized in 14 steps from (+)‐(R)‐limonene (4). The key step is the reductive vitamin‐B12‐catalyzed coupling of (R)‐5‐(2‐iodoethyl)‐6‐mehtylhept‐6‐en‐2‐one ethylene acetal (8) and methyl crotonate (3).
Carbocyclic Analogs of Nucleosides. Part 4. Preparation of enantiomerically pure analogs of purine nucleosides for the synthesis of sulfone‐linked oligonucleotide analogs
Authors: Jenny Thomas F. , Benner Steven A. 
Published: December 2004

AbstractCyclopentane derivatives bearing a 3‐(hydroxymethyl) group, a 4‐(2‐hydroxyethyl) functionality, and a nucleoside base are carbocyclic variants of nucleoside analogs previously described as building blocks for the preparation of oligonucleotide analogs having dimethylene sulfone (= methanosulfonylmethano) linking groups replacing the phosphodiester linking units found in natural oligonucleotides. These carbocyclic nucleoside analogs (e.g. 17 and 20) are stable to both acid‐catalyzed depurination and base‐catalyzed hydrolysis, in contrast with most non‐ionic analogs of oligonucleotides. Furthermore, they can be prepared with complete control over the stereochemistry at the ‘anomeric’ center. A procedure is given for preparing these purine‐nucleoside analogs via the construction of an enantiomerically pure carbocyclic skeleton (Schemes 1–3), followed by a Mitsunobu‐type reaction to introduce the purine‐base derivatives (Scheme 4). Furthermore, preliminary results for the coupling of these analogs to yield nucleoside dimers (e.g. 26) are also reported (Scheme 5).
Physicochemical and Structural Properties of Non‐Steroidal Anti‐inflammatory Oxicams
Authors: Tsai Ruey‐Shiuan , Carrupt Pierre‐Alain , Tayar Nabil El , Giroud Yvan , Andrade Pedro , Testa Bernard , Brée Françoise , Tillement Jean‐Paul 
Published: December 2004

AbstractUsing the five therapeutic oxicams 1–5, we showed that isosteric replacements result in remarkable changes in the physicochemical and structural properties of congeners. Thus, the acidity of the phenolic OH group is relatively higher in the oxicams containing a pyridinyl moiety, i.e. in piroxicam (1), tenoxicam (2), and lornoxicam, (3), due to their zwitterionic nature. This consequently influences their lipophilicity profile at different ionization states. Furthermore, partitioning behaviour in octan‐l‐ol/H2O and heptane/H2O systems suggests an internal H‐bond between the enolic OH and the amide CO group. The anionic oxicams readily partition into the octanol phase at pH 7.4 and not at all into the heptane phase. Only the partition coefficients of oxicams measured in the heptane/H2O system, but not in the octanol/H2O system, correlate with their transfer across the blood‐brain barrier. This implies that only the neutral form of oxicams crosses the blood‐brain barrier.
Epoxidierung von Cucurbitaxanthin A: Herstellung von Cucurbitaxanthin B und seines 5′,6′‐Epimeren
Authors: Deli József , Matus Zoltán , Molnár Péter , Tóth Gyula , Décsy Zoltán , Eugster Conrad Hans 
Published: December 2004

Epoxidation of Cucurbitaxanthin A: Preparation of Cucurbitaxanthin B and of Its 5′,6′‐EpimerCucurbitaxanthin A (= (3S,5R,6R,3′S)‐3,6‐epoxy‐5,6‐dihydro‐β,β‐carotene‐5,3′‐diol; 1) isolated from red pepper (Capsicum annuum var. longum nigrum) was trimethylsiylated and then epoxidized with monoperphthalic acid. After deprotection and chromatographic separation, cucurbitaxanthin B (= (3S,5R,6R, 3′S,5′R,6′S)‐3,6:5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐5,3′‐diol; 2) and 5′,6′‐diepicucurbitaxanthin B (= (3S,5R,6R, 3′S,5′S,6′R)‐3,6:5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐5,3′‐diol; 5) were obtained and carefully characterized. They show mirror‐like CD spectra and, therefore, emphasize the importance of the torsion angle of C(6)–C(7) on the electronic interaction between the polyene chain and the chiral end group.
Synthesis of (−)‐Pinidine via asymmetric, electrophilic enolate hydroxyamination/nitrone reduction
Authors: Oppolzer Wolfgang , Merifield Eric 
Published: December 2004

AbstractEnantiomerically pure(−)‐pinidine (1) has been synthesized in 18.5% overall yield by a nine‐step sequence starting from keto‐ester 2. The key step 5 → 6 involves an asymmetric, electrophilic enolate hydroxyamination. Diastereoselective hydrogenation of nirtone 6 ensures the cis‐relation between the substituents at C(2) and C(6) in piperidine 7.
Synthesis and Structure of η4‐Enone Complexes of Ruthenium(0)
Authors: Marcuzzi Alessandro , Linden Anthony , von Philipsborn Wolfgang 
Published: December 2004

AbstractA variety of [Ru(CO)2L(η4enone)] complexes (L = phosphines, phosphites, and arsines, enone = (E)‐4‐phenylbut‐3‐en‐2‐one) have been synthesized. 1H‐, 13C‐, and 31P‐NMR spectra are reported and the X‐ray structures of two Ru complexes with L  Ph3P(7), Et3P (10) and one Fe complex with L  Ph3P (14) are presented. All three compounds crystallize in the same monoclinic space group P21/n with a = 10.575(2) Å, b =9.213(2) Å, and c = 27.608(5) Å, β = 100.04(2)°, Z = 4 for 7, a = 10.276(3) Å, b = 12.935(3) Å, and c = 14.854(2) Å, β = 96.96(2)°, Z = 4 for 10, and a = 10.492(2) Å, b = 9.232(3) Å, and c = 27.129(3) Å, β = 98.67(2)°, Z = 4 for 14. The structures of the Ru complexes are compared with the Fe analogues. In the case of M  Ru and L  (EtO)3P, (MeO)3P, and (i‐PrO)3P (9, 11, and 13, respectively) stereoisomers could be detected by 31P‐NMR at room temperature, wich arise from rotation at the coordinated metal centre.
The 2H,2H‐INADEQUATE experiment: Detection of One‐ and Two‐Spin Double Quantum Coherences
Authors: Mons Hans‐Egbert , Bergander Klaus , Günther Harald 
Published: December 2004

AbstractThe INADEQUATE experiment for spin‐1 nuclei has been extended to deuteron spin systems of the AX, AA′ XX′, and AA′MM′X type. Measurements with (3,3‐D2)norcampher, 4‐chloro(2,3,5,6‐D4)pyridine, and (D5)pyridine revealed correlation peaks due to two‐spin double quantum coherences and additional one‐spin double quantum peaks with coordinates F1 = 2 ωi, F2 =(ωii = A, X) which were not observed in the 6Li, 6Li,‐INADEQUATE experiment described earlier.
Improved Purification of C60 and Formation of σ‐ and π‐Homoaromatic methano‐bridged fullerenes by reaction with alkyl diazoacetates
Authors: Isaacs Lyle , Wehrsig Arno , Diederich François 
Published: December 2004

AbstractA rapid and inexpensive method for the large‐scale purification of C60 is the simple filtration of the toluenesoluble extract of commercial fullerene soot through a short plug of charcoal/silica gel with toluene as the eluent. Reactions of C60 with ethyl and tert‐butyl diazoacetates in refluxing toluene lead to the formation of the (alkoxycarbonyl)methylene‐bridged isomers 1a–3a and 1b–3b, respectively, which can be equilibrated, upon further heating, into the single compounds 1a and 1b, respectively. Isomers 1a/b possess the methano bridge at the 6–6 ring junction, whereas structures 2a/b and 3a/b are bridged at the 6–5 junction. A dramatic influence of local and π‐ring current anisotropic effects of the fullerene sphere on the NMR chemical shifts of the methine protons in the bridge is observed: the chemical shifts of the protons located over a pentagon ring in 2a/b and over a hexagon ring in 3a/b differ by Δδ = 3.47 and 3.45 ppm, respectively. The analysis of the 13C‐NMR chemical shifts of the bridgehead C‐atoms and the 1J(C,H) coupling constants for the methano‐bridge atoms reveals conclusively that the 6‐5‐ring‐bridged structures 2a/2b and 3a/3b are π‐homoaromatic (‘open’ transannular bond) and the 6‐6‐ring‐bridged structures 1a/b are π‐homoaromatic (‘closed’ transannular bond). The electronic absorption spectra show that π‐homoconjugation in 2a/b and 3a/b represents a much smaller electronic perturbation of the original C60 chromophore than σ‐homoconjugation in 1a/b. The results of this study demonstrate an impressive linkage between the chemistry of methano‐bridged annulenes and methano‐bridged fullerenes.
An Efficient Enantioselective Synthesis of (—)‐Serricorole
Authors: Oppolzer Wolfgang , Rodriguez Inès 
Published: December 2004

AbstractThe cigarette beetle pheromone (–)‐serricorole (1) has been synthesized in 23% overall yield by an eight‐step sequence starting from N‐propionylsultam 3. The synthesis features asymmetric anti‐ and syn‐aldolizations 3 → 4 and 8 → 9, a non‐destructive N‐acylsultam cleavage with lithiated ethylphenylsulfone (10 → 12), and the smooth, Ti‐mediated cyclization of β‐acyloxy‐ketone 2 to dihydropyranone 14.
Stereocontrolled Syntheses of Polysubstituted 2,3‐Dihydro‐4H‐pyran‐4‐ones by cyclocondensation of β‐ acyloxy‐ketones
Authors: Oppolzer Wolfgang , Rodriguez Inés 
Published: December 2004

Abstractsyn‐β‐Acyloxy‐ketones 6 and an anti‐β‐acyloxy‐ketone 17 undergo smooth intramolecular enolate/ester condensations 6 → 18 and 17 → 19 when treated with TiCl4/EtN(i‐Pr)2. Thus, tri‐ and tetrasubstituted cis‐ or trans‐2,3‐dihydro‐4H‐pyran‐4‐ones are easily prepared in a stereoselective manner.
Lanthanide‐nitrate interaction in anhydrous acetonitrile and coordination numbers of the lanthanide ions: FT‒IR study
Authors: Bünzli Jean‐Claude G. , Milicic‐Tang Anita , Mabillard Catherine 
Published: December 2004

AbstractThe interaction between lanthanide ions LnIII (Ln = La, Nd, Sm–Dy, Er, Yb) and nitrate ions is investigated by FT‐IR spectroscopy in dilute anhydrous MeCN solution. The work is performed for ratios R = [NO]t/[LnIII]t ranging from 0 to 8 and for solutions generally 0.05M in LnIII, prepared from anhydrous lanthanide perchlorates Ln(ClO4)3. When nitrate is progressively added to the Ln(ClO4)3 solutions, the formation of [Ln(NO3)n](3−n)+ species is clearly evidenced by the FT‐IR spectra. All the NO3− ions are coordinated and bidentate. A quantitative study was performed using the v1 and v6 vibrational modes for coordinated NO ions. The average coordination numbers estimated for Nd, Eu, Tb, and Er in solutions of trinitrates are 9.0, 9.1, 8.3 and 8.2, respectively (±0.3 unit). In presence of an excess NO, these numbers become 9.8, 10.2, 10.0, 9.8, 9.9, and 9.9 (±0.3 unit) for La, Nd, Eu, Tb, Er, and Yb, respectively. No hexanitrato species forms under the experimental conditions used (R up to 8). The structural aspect of the various nitrato species is also investigated. In the pentanitrato species, all the ligands appear to be equivalent, while large inequivalences are observed for Ln(NO3)3 solutions. Since for the latter most of the absorption bands assigned to nitrate vibrations contain several components, a curve‐fitting procedure has been used for decomposing the v2, v4 and v6 vibrations. There is a considerable difference between LnIII ions, the nitrate inequivalences being larger in the middle of the series.
Ilwensisaponins A, B, C, and D: Triterpene Saponins from Scrophularia ilwensis
Authors: Çaliş İhsan , Zor Murat , Başaran A. Ahmet , Wright Athony D. , Sticher Otto 
Published: December 2004

AbstractFrom the aerial parts of Scrophularia ilwensis, four new triterpene saponins, ilwensisaponins A–D (1–4) were isolated. The structures of the compounds were elucidated using chemical and spectral data as 13β, 28‐epoxy‐3‐β‐{{[β‐D‐glucopyranosyl‐(1→2)]‐[α‐L‐rhamnopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→3)]‐β‐D‐fucopyranosyl}‐oxy} olean‐11‐en‐23‐ol (1), 3‐β‐{{[β‐D‐glucopyranosyl‐(1→2)]‐[α‐L‐rhamnopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→3)]‐β‐D‐fucopyranosyl}oxy}olena‐11, 13(18)‐diene‐23, 28‐diol (2), 3‐β‐{{[β‐D‐glucopyranosyl‐(1→2)]‐[α‐L‐rhamnopyranosyl‐(1→4)‐β‐Dglucopyranosyl‐(1→3)]‐β‐Dfucopyranosyl}oxy}‐11α‐methoxyolean‐ 12‐ene‐23, 28‐diol (3), and 3‐β‐{{[β‐D‐glucopyransoyl‐(1→2)]‐[α‐L‐rhamnopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→3)]‐β‐D‐fucopyranosyl}oxy}olean‐12‐ene‐11α,23,28‐triol(4).
Why Pentose‐ and Not Hexose‐Nucleic Acids??. Part VII. Pyranosyl‐RNA (‘p‐RNA’). Preliminary communication
Authors: Pitsch Stefan , Wendeborn Sebastian , Jaun Bernhard , Eschenmoser Albert 
Published: December 2004

AbstractQualitative conformational analysis of the entirety of conceivable hexo‐ and pentopyranosyl oligonucleotide systems derived from the diastereoisomeric aldohexoses (CH2O)6 and aldopentoses (CH2O)5 predicts the existence of a variety of pairing systems which have not been experimentally investigated so far. In particular, the analysis foresees the existence of a ribopyranosyl isomer of RNA (‘p‐RNA’), containing the phosphodiester linkage between the positions C(4′) and C(2′) of neighboring ribopyranosyl units. Double strands of p‐RNA oligonucleotides are expected to have a linear structure and to show purine‐pyrimidine and purine‐purine (Watson‐Crick) pairing comparable in strength to that observed in homo‐DNA. Experimentally, synthetic β‐D‐ribopyranosyl (4′→2′)‐oligonucleotides derived from adenine and uracil confirm this prognosis: adenine‐uracil pairing in p‐RNA duplexes is stronger than in the corresponding RNA duplexes. Importantly, adenine in p‐Ribo(A8) does not show (reverse‐Hoogsteen) self‐pairing, in sharp contrast to its behavior in the homo‐DNA series. The sheer existence of strong and selective pairing in a system that is constitutionally isomeric to RNA and can be predicted to have a linear structure has implications for the problem of RNA's origin. In this context, a comprehensive experimental study of the pairing properties of p‐RNA, of its potential for constitutional assembly, self‐replication, and intra‐duplex isomerization to RNA seems mandatory.
Stereoselectivity in Reactions of Metal Complexes. Part XVII. Synthesis of three new optically active triamines: 2,6‐Bis{[(2S)‐2‐(hydroxymethyl)pyrrolidin‐1‐yl]methyl}pyridine, 2,6‐bis{[(2S)‐2‐(methoxymethyl)pyrrolidin‐1‐yl]methyl}pyridine, and 2,6‐bis{{(2S)‐2‐[(benzyloxy)methyl]pyrrolidin‐1‐yl}methyl}pyridine. X‐ray structure and equilibrium behaviour of their copper(II) complexes
Authors: Bernauer Klaus , Chuard Thierry , Stoeckli‐Evans Helen 
Published: December 2004

AbstractThe three new optically active triamines derived from 2,6‐bis(aminomethyl)pyridine, i.e. 2,6‐bis{[(2S)‐2‐(hydroxymethyl)pyrrolidin‐1‐yl]methyl}pyridine (3a), 2,6‐bis{[(2S)‐2‐(methoxymethyl)pyrrolidin‐1‐yl]methyl}‐pyridine (3b), and 2,6‐bis{{(2S)‐2‐[(benzyloxy)methyl]pyrrolidin‐1‐yl}methyl}pyridine (3c), were synthesized. The equilibrium behaviour in solution and CuII complex formation were studied by acidimetric titration and by UV/VIS and CD measurements. It was found that in aqueous solution, 3a can coordinate one of the CH2OH groups to CuII upon deprotonation. X‐Ray crystal structures were determined for the complexes [Cu(3a)Cl]ClO4·H2O, [Cu(3b)Cl]ClO4, and [Cu(3c)Cl]ClO4. In the solid state, coordination of both the OH and the alkoxy groups was observed, and the three ligands are pentacoordinated.
Tritium Labelling of Naltrindole, a δ‐Receptor‐Selective Opioid Antagonist via 1‐Bromonaltrexone
Authors: Tóth Géza , Ötvös Ferenc , Hosztafi Sándor 
Published: December 2004

AbstractThe synthesis of [1,5′‐3H2]naltrindole (9) with labels at both the morphine skeleton and the indole moiety was carried out by catalytic tritiodehalogenation of 1,5′‐dibromonaltrindole (8) resulting in a specific activity of 46.1 Ci/mmol (1705 GBq/mmol). The brominated precursor was prepared by the Fischer indole synthesis starting from 1‐bromonaltrexone (7) and (4‐bromophenyl)hydrazine.
Investigation of an Olfactoryly Active Ring‐Like Conformer of a Chain‐Type Odorant, (3S)‐3,7‐dimethyloctanal, by computer calculation and graphics
Authors: Yoshii Fumiko , Hirono Shuichi , Moriguchi Ikuo 
Published: December 2004

AbstractThe odor of (3S)‐3,7‐dimethyloctanal, a chain‐type odorant, has some resemblance to that of ethyl (1 R, 6S)‐2,2,6‐trimethylcyclohexane‐1‐carboxylate, a ring‐type odorant. We investigated the ring‐like conformers of (3S)‐3,7‐dimethyloctanal. Two approaches, (i) systematic conformational analysis and (ii) construction of the initial structure by referring to the structure of the ring‐type odorant, were considered in the search for ring‐like conformers of the chain‐type odorant. As a result, it was found that two stable ring‐like conformers of (3S)‐3,7‐dimethyloctanal, obtained from the two approaches, resembled conformers of ethyl (1R, 6S)‐2,2,6‐trimethylcyclohexane‐1‐carboxylate in their three‐dimensional structural features. The shapes of the two ring‐like ones were not exactly the same but were quite similar. Therefore, the two ring‐like conformers were considered to approximate the olfactoryly active conformer that binds and stimulates the same odor receptor as that for ethyl (1R,6S)‐2,2,6‐trimethylcyclohexane‐1‐carboxylate. In addition, ring‐like conformers of another chain‐type odorant, 2‐methylpent‐2‐enal, were investigated to check the validity of the calculation method used.
Self‐Replication of Oligonucleotides in Reverse Micelles
Authors: Böhler Christof , Luisi Pier Luigi , Bannwarth Willi 
Published: December 2004

AbstractThe coupling between the tri(deoxynucleotides) d[(MeO)C‐G‐Ap] (1) and d[(NH2)Td5′‐C‐G‐] (2) to yield the phosphoramidate‐linked (hexadeoxy‐nucleotide) d[(MeO)C‐G‐Anh5′Td5′‐C‐G] (3) was investigated both in aqueous solution and in reverse micelles constituted of CTAB (cetyl(trimethyl)ammonium bromide) in hexane/pentan‐1‐ol 9:1. No siginificant difference was found concerning the yield and the kinetics of the reaction in the two systems. The coupling between 1 and 2 was also carried out in the presence of the template d[(MeO)C‐G‐A‐T‐C‐G] (4), an analogue of 3, so as to reproduce the conditions of template‐directed self replication. It was shown that the trinucleotide coupling in the presence of a template obeys the so‐called square‐root law both in H2O and in reverse micelles. No significant difference of the time course of the reaction in H2O and in reverse micelles was observed. This shows that self‐replication of oligonucleotides occurs within geometrically bounded structures, which represents a step forward in the mimicking of minimal life processes.
The Homoconjugated Electron‐Releasing Carbonyl Group of 1‐Methylbicyclo[2.2.1]hept‐5‐en‐2‐one. Regioselective syntheses of 5‐chloro‐ and 6‐chloro‐1‐methylbicyclo[2.2.1]hept‐5‐en‐2‐one
Authors: Kernen Philippe , Vogel Pierre 
Published: December 2004

AbstractSyntheses of (±)‐2‐exo‐cyano‐1‐methyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐endo‐yl acetate (1) and of (±)‐1‐methyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (2) are reported. The additon of PhSeCl to 1 afforded (±)‐5‐endo‐chloro‐2‐exo‐cyano‐1‐methyl‐6‐exo‐(phenylselenenyl)‐7‐oxabicyclo[2.2.1]hept‐2‐endo‐yl acetate (6), whereas 2 added to PhSeCl with the opposite regioselectivity giving (±)‐6‐endo‐chloro‐1‐methyl‐5‐exo‐(phenylselenenyl)‐7‐oxabicyclo[2.2.1]heptan‐2‐one (7). These adducts were converted into 5‐chloro‐1‐methyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (9) and 6‐chloro‐1‐methyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (10), respectively.
2‐(Tributylstannyl)‐1‐{[2‐(trimethylsilyl)ethoxy]methyl}‐1H‐indole: Synthesis and use as a 1H‐indol‐2‐yl‐anion equivalent
Authors: Palmisano Giovanni , Santagostino Marco 
Published: December 2004

AbstractPd‐Catalyzed reaction of 2‐(tributylstannyl)‐1‐{[2‐(trimethylsilyl)ethoxy]methyl}‐1H‐indole (5) with a variety of aryl, heteroaryl, vinyl, and allyl halides provides an efficient entry to the corresponding cross‐coupled products (see Table).
Synthesis and Characterization of (5′‐Deoxyadenosin‐5′‐yl)cobalamin ( = ‘Adenosylcobalamin’) Analogues Mimicking the Transition‐State Geometry of Coenzyme‐B12‐Dependent Rearrangements
Authors: Poppe László , Rétey János , Hull William E. 
Published: December 2004

AbstractA convergent synthesis of the five novel analogues 1a–e of (5′‐deoxyadenosin‐5′‐yl)cobalamin ( = ‘adenosylcobalamin’) is described. The analogues 1a–e carry oligomethylene chains (C3–C7) inserted between the central Co‐atom and the 5′‐O‐atom of the adenosine moiety and are thought to mimick the transition‐state geometry in coenzyme‐B12‐catalyzed rearrangement. All five analogues were characterized by NMR, UV, and FAB mass spectrometry.
Photochemistry of 6,6‐Dimethyl‐ and 2,2,6,6‐Tetramethyl‐2H,6H‐pyran‐3‐one
Authors: Er Erhan , Margaretha Paul 
Published: December 2004

AbstractThe title compounds 1a and 1b have been synthesized in two steps from the saturated pyran‐3‐ones 2a and 2b, respectively. Upon irradiation (254 nm or 350 nm) in dilute solutions (10−3−10−2M), compounds 1 undergo a formal [4 + 2] cycloreversion from the excited triplet state to give (2‐methylprop‐1‐enyl)ketene (11) and either formaldehyde or acetone, ketene 11 being trapped by H2O or MeOH to afford 4‐methylpent‐3‐enoic acid (5) or its methyl ester 4 in 75–85% isolated yield. In this (monomolecular) photoreaction, heterocycles 1 differ from their alicyclic counterparts, i.e., 4,4‐dimethylcyclohex‐2‐enone (10a) and 4,4,6,6‐tetramethylcyclohex‐2‐enone (10b), as no rearrangement to a 4‐oxabicyclo[3.1.0]hexan‐2‐one occurs. On the other hand, the photochemical behavior of pyranone 1a in bimolecular reactions (cyclodimerization, [2 + 2] cycloaddition to 2,3‐dimethylbut‐2‐ene) resembles that of enone 10a.