bluuebunny/crossref_metadata_2025 huggingface dataset:
Monoterpenoid chemistry. Part 3.. Stereoselective synthesis of the major oxygenated metabolites of trans‐sobrerol
Authors: Pellegata Renato , Dosi Ivana , Ventura Paolo , Villa Maurizio , Lesma Giordano , Palmisano Giovanni
Published: December 2004

The stereoselective synthesis of the major oxygenated metabolites of trans‐sobrerol (1) in optically active and/or racemic form is described.
Complexes of 2,2′,2″‐Nitrilotriphenol. Part 1. A Study of Bimolecular Nucleophilic Substitution at the Boron Atom
Authors: Müller Edgar , Bürgi Hans‐Beat
Published: December 2004

The tetradentate ligand 2,2′,2″‐nitrilotriphenol forms a boron complex III with an intramolecular, transannular N→B dative bond of 1.68 Å in a strained tricyclo[3.3.3.0]undecane chelating system. The complex reacts with nitrogen bases L, such as pyridine, quinuclidine and others, to form complexes III‐L, in which the intramolecular B–N bond is replaced by one between B and the external nucleophile. In solution, this displacement reaction is reversible. It was studied by temperature‐dependent NMR spectroscopy. The resulting reaction and activation parameters suggest that the reaction is a bimolecular nucleophilic substitution (SN2).
The Hydrolysis of Ethyl 1‐Methyl‐2,4‐cyclopentadiene‐1‐carboxylate by Nonenzymatic and Enzymatic Methods. Carbon‐Carbon vs. Carbon‐Oxygen Bond Cleavage
Authors: Burger Ulrich , Erne‐Zellweger Dominique , Mayerl Christa
Published: December 2004

The title ester 5 is shown to undergo C–C bond cleavage under the conditions of basic ester hydrolysis (KOH/EtOH) with formation of potassium ethyl carbonate (6) and the tautomeric methylcyclopentadienes 7 and 8. In contrast, porcine liver esterase (PLE, EC 3.1.1.1) cleanly hydrolyses 5 to give the isolable 1‐methyl‐2,4‐cyclopentadiene‐1‐carboxylic acid (13). The latter undergoes thermal dimerization with conservation of the geminal‐substitution pattern. The configuration of the Diels‐Alder adduct 17 is ascertained by it photochemical transformation into bishomocubane dicarboxylic acid 12, easily distinguished by its C2 symmetry. Under the conditions of acid‐catalyzed hydrolysis, dimerization of ester 5 and polymerization prevail, unless low acid concentration is used. The dimer 9 of 5 has one ester function that is reluctant to undergo basic hydrolysis.
Synthesis of biopterin from neopterin? The formation of pyrrolo[1,2‐f]pteridins upon side‐chain activation of neopterin
Authors: Kaiser Ado , Wessel Hans Peter
Published: December 2004

The formation of derivatives of L‐neopterin (2) is investigated with respect to a possible transformation into L‐biopterin (1). High‐yield syntheses of isopropylidene and benzylidene derivatives 5 and 7, respectively, are described. Activation of the primary C‐atom in the side chain of neopterin leads to formation of pyrrolo[1,2‐f]‐pteridins via oxonium‐ion intermediates.
Synthetic Models of the Active Site of Cytochrome P‐450. 1st Communication. The Synthesis of a Doubly‐Bridged Iron(II)‐Porphyrin Carrying a Tightly Bound Thiolate Ligand
Authors: Stäubli Beat , Fretz Heinz , Piantini Umberto , Woggon Wolf‐Dietrich
Published: December 2004

The doubly‐bridged iron(II)‐tetraphenylporphyrin derivative 6, carrying a sterically fixed S− ligand in the ‘proximal’ position and the substrate at the ‘distal’ site, was synthesised as an enzyme model for cytochrome P‐450. Compound 36, the CO complex of 6, displays a split Soret band (403 and 457 nm) similar to the native cytochrome P‐450.
Stereoselective Syntheses of Tetrahydrolipstatin and of an Analogue, Potent Pancreatic‐Lipase Inhibitors Containing a β‐Lactone Moiety
Authors: Barbier Pierre , Schmeider Fernand , Widmer Ulrich
Published: December 2004

Tetrahydrolipstatin (1) and itsanalogue 2 are representatives of a new class of pancreatic‐lipase inhibtors. Two stereoselective synthetic approaches are described.
Diels‐Alder‐Reaktionen von 2′‐substituierten 3‐Vinyl‐1H‐indolen zu neuen anellierten Indol‐und Carbazol‐Derivaten
Authors: Pfeuffer Ludwig , Pindur Ulf
Published: December 2004

Diels‐alder Reactions of 2′‐Substituted 3‐Vinyl‐1H‐indoles to New Annellated Indole and Carbazole Derivatives

New regio‐ and stereoselcctive cycloadditions between 2′‐ substituted 3‐vinyl‐lH‐indoles and the dienophiles N‐Phenylmaleimide, dimethyl acetylendicarboxylate, and methyl acrylate are reported. Products include some new carbazole derivatives and Michael adducts. In the presence of AlCl3 as dicnophile‐activating catalyst, ‘endo’ preference for deriving cycloadducts is observed. In some cases, Michael addition competes with[4+2] cycloaddition.
The Ionization Energies of Tetrazinodi(heteroarenes)
Authors: Lecoultre Jacques , Heilbronner Edgar , Eichenberger Thomas , Balli Heinz
Published: December 2004

The ionization energies of four [1,2,4,5]tetrazinodi(heteroarenes) of C2h Symmetry have been measured by PE spectroscopy. It is found that the first ionization energy is very low (6.2 eV to 6.4 eV) and rather independent of the size and/or topology of the molecules. This is explained, by comparison with the results of a simple MO treatment, as being due to strong localization of the HOMO (of Au symmetry) on the [1,2,4,5]tetrazino moiety of the molecules. The PE‐spectroscopic data are shown to be in agreement with the UV/VIS‐and electrochemical‐oxidation data published previously.
Die Position 5 im Oxotremorin‐Gerüst: Eine zentrale Stelle für die Steuerung der Aktivität am muscarinischen Rezeptor
Authors: Amstutz René , Closse Annemarie , Gmelin Gernot
Published: December 2004

Position 5 at the Oxotremorine Skeleton as the Stearing Position for Activity at the Muscarinic Receptors

Substitution of the Ch2 group at position 5 of oxotremorine (2) by electronegative atoms like O‐ or N‐atom, or by sterically bulkier groups like methyl, N‐formyl, or N‐acetyl Changes the pharmacological profile of oxotremorine drastically. The O‐ and N‐analogues were potent but unselective (M1/M2) muscarinic agonists. The methyl analogue ((R)‐BOK‐1) is a muscarine antagonist which is 10 times more potent on the ganglion cervical superius (pA2 = 9.3) than pirenzepine and is able to distinguish between the ileal and ganglion receptor by a factor of 100. The N‐formyl derivative differentiates between the two receptors by a factor of 500 with a potency comparable to pirenzepine. The two M1‐selective antagonists have higher affinity to the rat‐ganglion receptors compared to the affinity to rat‐cortex homogenate. The synthesis and the pharmacological activity of several new oxotremorine analogues are discussed.
Isolation and Absolute Configuration of β,β‐Carotene Diepoxide
Authors: de Almeida Ligia Bicudo , De Vuono Camargo Penteado Marilene , Britton George , Uebelhart Peter , Acemoglu Murat , Eugster Conrad Hans
Published: December 2004

The 5,6:5′,6′‐diepoxy‐5,6:5′,6;‐tetrahydro‐β,β‐carotene, isolated from tubers of a white‐fleshed variety of sweet potato (Ipomoea batatas LAM.) has been assigned the (5R,6S,5′R,6′S)‐chirality on the basis of its HPLC, UV/VIS, and CD data.
Anwendung der Azirin/Oxazolon‐Methode in der Peptid‐Chemie: Synthese von Modell‐Tripeptiden
Authors: Wipf Peter , Heimgartner Heinz
Published: December 2004

The Azirine/Oxazolone Method in Peptide Chemistry: Synthesis of Tripeptide Models

Tripeptides 5, containing an α,α ‐disubstituted α‐amino acid and ethyl p‐aminobenzoate, were synthesized in high yield by application of the azirine/oxazolone method (Table 2). In this versatile approach for the incorporation of disubstituted residues into the peptide chain, N‐protected peptides or amino acids are coupled with 2,2‐dialkyl‐3‐amino‐2H‐azirines and, after the selective hydrolysis of the newly formed C‐terminal amid bond, further condensed with amino components via in situ generated oxazole‐5(4H)‐ones in the presence of additives (Scheme 1). A comparison with conventional procedures clearly demonstrates the advantages of this new method that works equally well with β‐branched, cyclic, or acyclic disubstituted amino acids.
Silicon‐Directed Nazarov Cyclizations. Part VI. The anomalous cyclization of vinyl dienyl ketones
Authors: Denmark Scott E. , Hite Gary A.
Published: December 2004

Reactions, of various vinyl dienyl ketones (see la–e, li) with FeCl, give rise to β,γ‐unsaturated α‐vinyl‐cyclo‐pentenones (see 2a–e, 2i, Table 2). The reaction succeeds for vinyl dienyl ketones with substituents on either double bond. Aryl dienyl and alkyl dienyl ketones (see 1f–h) do not cyclize cleanly. The effects of substituents on the rate of reaction is discussed in terms of the mechanism of the rearrangement. A 13C‐labeling study establishes the pathway as an unusual 1‐hydroxypentadienyl‐cation electrocyclization to a cyclopentenyl cation which collapses via a pinacol rearrangement to the α‐vinyl ketone.
Norbornanes. Part 20. Inductivity and bridging in 2‐norbornyl cations
Authors: Bielmann Rolf , Fuso Francesco , Grob Cyril A.
Published: December 2004

The solvolysis rates and products of several 1‐substituted 2exo‐ and 2‐endo‐norbornyl p‐toluenesulfonates 7 and 8, respectively, have been determined. Hydrolyses of these epimeric tosylates yielded rearranged products in varying amounts, except when the substituent was COOCH3 or CN. The logarithms of the rate constants (log k) for the endo‐series 8 correlated linearly with the corresponding inductive constants σ with a reaction constant ρI of −1.24. On the other hand, log k values for the exo‐series 7 appear to fit two regression lines, the first line (ρI = −1.90) defined by the tosylates that ionize, with rearrangement, to the tertiary cations 11, the second (ρI = −1.86) by the tosylates 7 (R = H, COOCH3, and CN) that ionize to an asymmetrically bridged secondary cation 19. These results confirm the unique participation of C(6) with a ρI of −2.00 in the ionization of 2‐exo‐nor‐bornyl tosylate.
Photochemical Reactions. 149th Communication. Photochemistry of 7,8‐dihydro‐4‐hydroxy‐β‐ionone and derivatives
Authors: Pascual Alfons , Bischofberger Norbert , Frei Bruno , Jeger Oskar
Published: December 2004

The photolysis of 7,8‐dihydro‐4‐hydroxy‐β‐ionone (6) was investigated together with its acetate and isopropyl ether 7 and 8, respectively. Irradiation (λ > 245 nm) of 6 in MeCN or i‐PrOH at temperatures between 25° and −65° leads to the tricyclic ethers 9, 10 and 13A + B, and to the spirocyclic ethers 11 and 12, which are all known types of photoproducts, previously obtained on photolysis of 7,8‐dihydro‐β‐ionone (1). The same types of products are obtained on irradiation of the acetate 7 and the isopropyl ether 8. On the other hand, irradiation of the hydroxy compound 6 in MeCN or i‐PrOH at temperatures between −35° and −65° leads to the new tricyclic tertiary alcohols 14 and 15 as the major products. Their formation involves an intramolecular trapping of a carbocation by the neighbouring OH group, thus, supporting the previously proposed mechanism of the transformation 1 → 5. For structure proof, the tricyclic alcohol 14 and the pheny1 carbamate 42, derived from 9, were subjected to X‐ray analysis.
A new synthesis of N‐acetylneuraminic acid
Authors: Csuk René , Hugener Martin , Vasella Andrea
Published: December 2004

A new synthesis of N‐acetylneuraminic acid (Neu5Ac; 28) via aldehyde 10 is described. The aldehyde 10 was obtained from N, acetyl‐D‐glucosamine (11; 5 steps, overall yield ca. 6%) or from D‐glucono‐1,5‐lactone (17; 6 steps, overll yield ca 57%). Thus, on the one hand, N‐acetyl‐D‐mannosamine (12), obtained from 11, was transformed into the known dithioacetal 14 and hence into the (ethylthio)dihydrooxazole 16, which was cleaved under weakly acidic conditions to the aldehyde 10. On the other hand, the known ester 18, obtained from 17, was sulfonylated and further transformed via the azide 20 into the N‐acetyl‐D‐mannonate 22. Reduction of 22 to 23 and oxidation of 23 with ‘periodinane’ again gave 10. The aldehyde 10 was treated with the organozinc reagent 8 obtained from tert‐butyl 2‐(bromomethyl)acrylate (2) to yield predominantly 24, which was transformed (two steps) into the 2‐methylidene‐D‐glycero‐nononic acid 27 and hence into Neu5Ac (28).
Kurze Totalsynthesen von (±)‐Sativen und (±)‐cis‐Sativendiol
Authors: Sigrist Rofl , Rey Max , Dreiding André S.
Published: December 2004

Short Total Syntheses of (±)‐Sativene and (±)‐cis‐Sativenediol

Our approach to (±)‐sativene (7) and (±)‐cis‐sdtivenediol (9) involves: (a) reaction of 3‐methylbutanoyl chloride with Et3N/cyclopentadiene to give the endo‐isopropyl‐ketone 1 (here improved to 71%), (b) NBS bromination of 1 to a 5:1 mixture (87%) of the bromo‐ketones 2 and 3, (c) NFD‐reaction sequence initiated by the attack of 1,2‐butadienyl titanate (complex of 15, obtained from 2‐butine) on 2/3 to afford 52% of the brexenone derivative 4 (along with 8% of its epimer 16), (d) addition of dibromomethane to 4 forming 63% of the diene‐alcohol 5 (along with 13% of the diene‐carbaldehyde 38), and (e) carbenoid ring‐expansion with MeLi applied to 5 resulting in 41% the diene‐ketone 6 (along with 15% of a 1:3 mixture of the diene‐ketones 32 and 33). Wolff‐Kishner reduction of 6 led to 81% of (±)‐sativene (7), when enough O2 was present, but to 97% of the diene 8 in the strict absence of O2. (±)‐cis‐Sativenediol (9) was obrained (86%) by OsO4 hydroxylation of 8. The brexenone derivatives 4 and 16 (6:1, 50%) were also produced when the NFD‐reaction sequence was applied to the isomeric bromo‐ketone mixture 13/13 (1:3). The latter was obtained by NBS bromination of 10, which in turn was available by base epimerization of 1, followed by destructive removal of unreacted 1 by repeated gas‐flow thermolysis. An analogous (less convenient) route to (±)‐sativene (7) passed through a series of dihydro compounds (the ene series) it started with the methylidene‐ketone 36, which was the product (97%) of a partial hydrogenation of 4. Addition of dibromomethane to 36 led t 62% of the methylidene‐alcohol 39 (along with a little tetracyclic ether 40). Carbenoid ring expansion of 39 with MeLi afforded ca. 42% of the methylidene‐ketone 41 (along with 7% of the methylidene‐ketone 43 or, under slightly different condition, along with 9% of the methylidene‐ketone 42 and 10% of the methylidene‐carabaldehyde 44). The methylidene‐alcohol 39 and the methylidene‐ketone 43 were also obtained by partial hydrogenation of 5 and 33, respectively. Wolff‐Kisher reduction converted 41 into (±)‐sativene (7 99%); the same conditons applied to 42 afforded only ca. 8% 7 (along with three other hydrocarbons, one of them (ca. 21%) probably being (±)‐copacamphene (45)). In the diene series, the two succeeding reactions (4→5 and 5→6) competed with the same side reaction, a rearrangement leading to the brendene‐aldehyde 38. In the ene series, the corresponding dihydro‐by‐product 44 was found in the reacton 39→41, but not during 36→39. These side reactons could largely be suppressed by keeping the reaction temperature low. An explanation is proposed.
Axially Dissymmetric Bis(triaryl)phosphines in the Biphenyl series: Synthesis of (6,6′‐dimethylbiphenyl‐2,2′‐diyl)bis(diphenylphosphine) (‘BIPHEMP’) and analogues, and their use in Rh(I)‐catalyzed asymmetric isomerizations of N,N‐diethylnerylamine
Authors: Schmid Rudolf , Cereghetti Marco , Heiser Bernd , Schönholzer Peter , Hansen Hans‐Jürgen
Published: December 2004

The axially dissymmetric diphosphines (−)‐(R)‐ and (+)‐(S)‐(6‐6′‐dimethylbiphenyl‐2,2′‐diyl)bis(diphenyl‐phosphine) ((−)‐(R)‐10 and (+)‐(S)‐10; ‘BIPHEMP’) have been synthesized, starting from (R)‐ and (S)‐6,6′‐dimethylbiphenyl‐2,2′‐diamine ((R)‐ and(S)‐16), respectively, via Sandmeyer reaction, liathiation, and phosphinylation. Moreover, racemic 4,4′‐ dimethyl‐ and 4,4′‐bis(dimethylamino)‐substituted analogues 11 and 12 respectively, and the 6,6′‐bridged analogues 1,11‐bis(diphenylphosphino)‐5,7‐dihydrodibenz[c,e]oxepin (13) were synthesized and resolved into optically pure (R)‐ and(S)‐enantiomers via complexation with di‐μ‐chlorob is {(R)‐2‐[1‐(dimethylamino)ethyl]pheny‐CN}dipalladium(II) ((R)‐18). The molecular structures of the diphosphines (S)‐10 and (R)‐13 and of two derived cationic Rh(I) complexes,[Rh((S)‐ 10)(nbd)]BF4 and [Rh((R)‐ 13)(nbd)]BF4 were determined by x‐ray analyses. Absolute configurations were established for (+)‐(S)‐ 10 by X‐ray analyses of both the free diphosphine and of the derived Rh(I) complex, and for (−)‐(R)‐ 13 by X‐ray analysis of the derived Rh(I) complex. Configurational assignments for the substituted BIPHEMP analogues 11 12 were achieved by means of 1H‐NMR comparisons. The BIPHEMP ligand 10 and analogues 11, 12 and 13 are the first examples of optically active bis(triaylphosphines) containing the axially dissymmetric biphenyl moiety. All these new diphosphines proved to be excellent asymmetry‐inducing ligands in Rh(I)‐catalyzed isomerizations of N,N‐diethylnerylamine affording citronellat enamine of 98‐99% ee.
Isolation from the Mediterranean Stolonifern Coral Sarcodictyon roseum of Sarcodictyin C, D, E, and F, novel diterpenodic alcohols esterified by (E)‐ or (Z)‐N(1)‐methylurocanic acid. Failure of the carbon‐skeleton type as a classification criterion
Authors: D'Anbrosio Michele , Guerriero Antonio , Pietra Franceseco
Published: December 2004

It is shown here that the stoloniferan coral Sarcodictyon roseum of east Pyrenean waters contains four novel diterpenoids, sarcodictyin C ((−)‐3), D ((−)‐4), E ((+)‐5), F ((+)‐6), which are related to sarcodictyin A ( = (−)‐(4R,4aR,7R,10S,11S,12aR,1Z,5E,8Z‐7,10‐epoxy‐3,4,4a,7,10,11,12,12a‐octahydro‐7‐hydroxy‐6‐(methyoxycarbonyl)‐1,10‐dimethyl‐4‐(1‐methylethyl)‐benzocyclodecen‐11‐yl (E)‐N1‐methylyrocanate; ((−)−1), previously isolated from the same coral. Sarcodictyin C ((−)‐3) and D ((−)‐4) and the 3α‐hydroxy and 3α‐acetoxy derivatives of (−)‐1), sarcodictyin E ((+)‐5) is the (Z)‐urocanate isomer of (−)‐3), and sarcodictyin F ((+)‐6) is the 1α‐hydroxy‐2‐ene isomer of (−)‐3. In all cases, the nine‐membered ring is locked, and the molecule stabilized, by the urocanic appendage; when this is removed in MeOH/KOH, the C(11)–O− function is free to attack at C(5), and retro‐condensations then lead to the ring‐contracted butenolides 11 (from (−)‐3) or 10 (from(−)‐1) with extrusion of the hydroxyfuran nucleus (Scheme 3). Under the same conditions, with (−)‐3, the C(3)‐O− group competitively attacks at C(5), the hydroxyfuran nucleus is expelled, and aldehyde 14 is formed. Peculiarly, in the reaction of (−)‐3 with MeOD/KOD, the ring‐contracted butenolide 17 contains D at the 4′‐ax position. The sarcodictyins are unique in these chemical properties, not shared by the cladiellanes which have the same C‐skeleton.
Synthese neuer Aryl‐(3,‐dichloro‐4‐pyridazinly)‐ketone und ihre Reaktion mit N,N‐Dinucleophilen
Authors: Eichhorn Thomas A. , Piesch Steffen , Ried Walter
Published: December 2004

Synthesis of New Aryl (3,6‐Dichloro‐4‐pyridazinyl) Ketones and their Reaction with N,N‐Dinucleophiles

The synthesis of the new aryl (3,6‐dichloro‐4‐pyridazinyl) ketones 3a–e vïa Friedel‐Crafts acylation of the aromatic compounds 2a–e with 3,6‐dichloro‐4‐pyridazincarbonyl chloride (1) is described. The ketones 3a–e cyclized with N,N‐dinucleophilic reagents to the 3‐aryl‐5‐chloro‐l H ‐pyrazolo[3,4‐c]pyridazines 4a–d, and 3a–c are converted into the 3‐aryl‐5‐chloro‐l H ‐pyrazolo[3,4‐c]pyridazin ‐ l ‐ethanols 5a–c and to the hitherto unknown ring system of the 5‐aryl‐3‐chloro‐7,8‐dihydro‐9 H ‐pyridazino[3,4‐e][1,4]diazepines (6a‐c).
8‐Aza‐7‐deaza‐2′‐deoxyguanosine: Phosphoramidite synthesis and properties of octanucleotides
Authors: Seela Frank , Driller Hansjürgen
Published: December 2004

Base‐modified octanucleotides derived from d(G1–G2–A–A–T–T–C–C–) (11) but containing 8‐aza‐7‐deaza‐2′‐deoxyguanosine (2) instead of 2′‐deoxyguanosine (1) have been prepared by solid‐phase synthesis employing P(III) chemistry. Isobutyrylation of 2, followed by 4, 4′‐dimethoxytritylation and subsequent phosphitylation yielded the methyl or the cyanoethyl phosphoramidites 6a or 6b, respectively. They were used as building blocks in automated DNA synthesis. The resulting octanucleotides 12–14 containing 2 showed increased Tm values compared to the parent oligomer 11. The oligomers 11–14 were employed as sequence‐specific probes in endo‐deoxyribonuclease Eco RI oligonucleotide recognition. Whereas displacement of dG‐2 (enzymic cleavage site of 11) abolished phosphodiester hydrolysis, replacement of dG‐1 enhanced the cleavage rate compared to 11.
Präparative chromatographische Enantiomerentrennung von synthetisch nützlichen cyclischen Acetalen
Authors: Seebach Dieter , Müller Stefan G. , Gysel Urs , Zimmermann Jürg
Published: December 2004

Preparative Chromatographic Resolution of Synthetically Useful Cyclic Acetals

Racemic cyclic acetals derived from aldehydes and glycine, glycolic acid, thioglycolic acid, formylacetic acid, and acetoacetic acid (oxazolidinones 4–13, dioxolanones 14, 15, oxathiolanone 16, dioxinones 17–23) are resolved by preparative high‐pressure liquid chromatography on silica gel coated with the polymer from N‐acryloylphenylalanine ethyl ester (Chiraspher®). The separation factors α range from1,1 to 2,4. Use of a Prepbar®‐chromatography system allows injection of several grams at a time. The enantiomeric acetals thus obtained are fully characterized. First application to amino‐acid synthesis are mentioned.
From Dichlorocyclopropanes to Furans and Cyclopentadienes via Vinylcarbenes
Authors: Müller Paul , Pautex Nicole
Published: December 2004

Base‐induced elimination of dichlorocarbene adducts 2 to 9‐alkoxyphen threnes 1 leads to furans 6, presumably via cyclopropenes 3 which undergo rearrangement to vinylcarbenes 4 and CH insertion. By the same sequence, the 9‐substituted alkylphenanthrene adduct 10 and 14 afford cyclopentadienes 11 and 15. Carbene adducts of simple enol ethers, however, react differently and give preferentially 2‐chloroalken‐2‐ones.
Intramolecular Dynamics of Tetranuclear Carbonyliridium Cluster Compounds. Part II. Disubstituted complexes with one chelating ligand. Crystal structure of [Ir4(CO)7(μ‐CO)3(1,5‐cyclooctadiene)]
Authors: Strawczynski Andrés , Ros Renzo , Roulet Raymond , Grepioni Fabrizia , Braga Dario
Published: December 2004

The two complexes [Ir4(CO)10(diarsine)] (1) and [Ir4(CO)10(1,5‐cyclooctadiene)] (2) bear a bidentate ligand chelating one metal atom of the basal face of the Ir4 tetrahedron. However, they differ in fluxional behaviour as observed by 2D‐exchange and variable‐temperature 13C‐NMR. The CO‐site exchange with lowest activation energy proceeds via an unbridged intermediate in 2, whereas that in 1 occurs via a concerted edge‐bridging of CO's to an alternative face of the metal core. This difference is apparently related to different ground‐state geometries: the basal CO's are symmetrically bridging in 2, whereas two CO's are semi‐bridging in 1. The molecular structure of 2 was determined by single crystal X‐ray diffractometry. The crystals are orthorhombic, space group Pbca, a = 11.651(4), b = 13.118(3), c = 28.64(1)Å. The idealized molecular symmetry is Cs. The diolefin chelates a basal Ir‐atom replacing an axial and a radial CO group on the tetrahedral metal‐atom framework.
Versuche zur Synthese von Calicen aus trisubstituierten Cyclopropanen und Cyclopentenon
Authors: Weber Andreas , Galli Roberto , Sabbioni Gabriele , Stämpfli Urs , Walther Stefan , Neuenschwander Markus
Published: December 2004

Attempted Synthesis of Calicene from Trisubstitued Cyclopropanes and Cyclopentenone

The Li carbenoids 4, prepared by treatment of substituted 1,1‐dihalocyclopropanes with BuLi, are reacted with cyclopent‐2‐enone under thermodynamic and kinetic control (Scheme 1). In general, the latter procedure gives better yields of cyclopropylcyclopentenols 5a–e, but the reaction seems to be controlled mainly by the steric and electronic properties of the substituent Y. So, with 4b and 4e, the main reaction is the attack of the carbenoid at C(1) of cyclopent‐2‐enone, while 4a (Y = PhS) predominantly deprotonates the ketone (Scheme 4). Whereas 5d and 5e can easily be converted to the dihydrocalicenes 6d and 6e (Scheme 6), the attempted elimination of H2O from 5a–c leads to the rearranged products 13–2 due to the opening of the cyclopropane ring (Scheme 5). Finally, the generation of the parent compound 2 from the silylated precursor 6d is attempted: treatment with MeO− gives the addition products 18A/18B, while the reaction with Br2 provides 19 by a bromination/dehydrobromination sequence (Scheme 7).
Asymmetric Diels‐Alder reactions: X‐Ray crystal‐structure analysis of [N‐((E)‐But‐2‐enoyl)bornane‐10,2‐sultam]tetrachlorotitanium
Authors: Oppolzer Wolfgang , Rodriguez Inès , Blagg Julian , Bernardinelli Gérald
Published: December 2004

An X‐ray diffraction analysis of the crystalline complex 2b (MLn  TiCl4) shows a chelation of the carbonyl O‐atom and the upper SO2 O‐atom by TiCl4, a slightly pyramidal N‐atom, and a π ‐face‐stereoselective shielding of the C(α)‐Si face by the CH2(3) group. The Ti‐atom is in a pseudo‐octahedral environment.
C45 und C50‐Carotinoide. 6. Mitteilung. Synthese eines optisch aktiven cyclischen C20‐Bausteins und von Decaprenoxanthin (= (2R, 6R, 2′R, 6′R)‐2,2′‐Bis(4‐hydroxy‐3‐methylbut‐2‐enyl)‐ϵ, ϵ‐carotin)
Authors: Gerspacher Marc , Pfander Hanspeter
Published: December 2004

C45‐ and C50‐Carotenoids: Synthesis of an Optically Active Cyclic C20‐Building Block and of Decaprenoxanthin ( = (2R, 6R, 2′R, 6′R)‐2,2′‐Bis(4‐hydroxy‐3‐methylbut‐2‐enyl)‐ϵ, ϵ‐carotene)

The synthesis of the optically active cyclic C20‐building block (R, R)‐15 and of the optically active C50‐carotenoid (2R, 6R, 2′R, 6′R)‐decaprenoxanthin (1) starting from (‐)‐β‐pinene ((S)‐2) is reported.
Photo‐oxygenation of Styrenic Estrogens: Product characterization and kinetics of the dye‐sensitized photo‐oxygenation of 9,11‐didehydroestrone derivatives
Authors: Planas Antoni , Lupon Pilar , Cascallo Montse , Bonet Juan‐Julio
Published: December 2004

The dye‐sensitized photo‐oxygenation of 3‐hydroxyestra‐1,3,5(10), 9(11)‐tetraen‐17‐one (8) gives a complex mixture from which only the 1,4‐endo‐peroxide 10 can be isolated in low yield. In contrast, the 3‐methoxy derivative 9 yields the C‐seco‐aldehyde 11 as a major product, suggesting that 1,2‐dioxetane is a primary photo‐oxygenation intermediate. As the electron‐donating character of the substituent at C(3) decreases in the sequence 12 (R = PhCO), 13 (R = Ac), and 14 (R = Ts), the rate constant in substrate disappearance becomes drastically smaller as compared with 8 and 9, and no photoproducts are detected. The results are rationalized by means of electronic and conformational factors.
Ring‐opened analogues of Ambrox®: Synthesis and Structure‐Odour relationships
Authors: Winter Beat
Published: December 2004

Eight bicyclic ether derivatives 11–18, related to the tricyclic odorant Ambrox® (1) and its analogues 2–6 by formal heteroring‐opening, have been prepared; their odoriferous activity/in activity is correlated with the steric accessibility of the ether O‐atom, calculated by computer‐aided molecular modeling.
New Irone‐Related Constituents from the essential oil of Iris germanica L.
Authors: Maurer Bruno , Hauser Arnold , Froidevaux Jean‐Claude
Published: December 2004

Twenty irone‐related compounds 1–20 containing from 10 to 16 C‐atoms have been identified for the first time in commercial Iris oil of Moroccan origin (Iris germanica L.). Most of the structures and the absolute configurations of natural 6, 16, and 17 are corroborated by partial synthesis. The organoleptic properties of some of the new constituents are discussed.
Aplysinopsin‐type alkaloids from Dendrophyllia sp., a scleractinian coral of the family dendrophylliidae of the philippines, facile photochemical (Z/E) photoisomerization and thermal reversal
Authors: Guella Graziano , Mancini Ines , Zibrowius Helmut , Pietra Francesco
Published: December 2004

The dendrophylliid Dendrophyllia sp. of Palawan contains the indole alkaloids 2′‐demethylaplysinopsin (4) and 2′‐demethyl‐3′‐N‐methylaplysinopsin (6) and their 6‐bromo analogues in H (Z/E) ratio larger than 95:5; these mixtures undergo facile photoisomerization to give mixtures richer in the (E) stereoisomer which undergo thermal isomerization to give back the original mixtures.
Der Zugang zum Antitumor‐Antibiotikum CC‐1065 mittels Hetero‐Cope‐Umlagerung von Vinyl‐N‐phenylhydroxamaten
Authors: Martin Pierre
Published: December 2004

The Access to the Three Subunits of the Antitumor Antibiotic CC‐1065 by Hetero‐Cope Rearrangement of Vinyl N‐Phenylhydroxamates.

The use of the hetero‐Cope rearrangement of vinyl N phenylhydroxamates to indoles for the preparation of the 1,2‐dihydro‐3H, 6H‐benzo[1,2‐b:4,3‐b′]dipyrrole skeleton, the structural subunits characteristic of the antitu‐mor antibiotic CC‐1065 as well as the phosphodiesterase inhibitors PDE‐I and PDE‐II is described.
Aromatization of tetrahydrocyclopropa[a]naphthalenes: An alternative synthesis of 1H‐Cyclopropa[a]naphthalene
Authors: Müller Paul , Bernardinelli GéRald , Thi Huong Can Godoy‐Nguyen
Published: December 2004

1H‐Cyclopropa[a]naphthalene (1a) is accessible via reduction of the dichloro compound 1c with LiAlH4/AlCl3. Several derivatives of tetrahydrocyclopropa[a]naphthalene were synthesized. However, contrary to their 1,1‐dihalogeno analogues, they afforded no cycloproparenes upon attempted aromatization.
Synthese von Plectranthonen, diterpenoiden Phenanthren‐1,4‐chinonen
Authors: Kaliakoudas Dimitrios , Eugster Conrad Hans , Rüedi Peter
Published: December 2004

Synthesis of Plectranthons, Diterpenoid Phenanthrene‐1,4‐diones

The following phenanthrene‐1,4‐diones have been synthesized by using the photocyclization of the corresponding highly substituted stilbenes as the key step: 3‐hydroxy‐5,7,8‐trimethyl‐2‐(prop‐2‐enyl)phenanthrene‐1,4‐dione (1), (RS)‐, (R)‐, and (S)‐2‐[3‐hydroxy‐5,7,8‐trimethyl‐1,4‐dioxophenanthren‐2‐yl]‐1‐methylethyl acetate (2, 31, and 32, resp.), 3‐hydroxy‐7,8‐dimethyl‐2‐(prop‐2‐enyl)phenanthrene‐1,4‐dione (3), 3‐hydroxy‐7,8,10‐tri‐methyl‐2‐(prop‐2‐enyl)phenanthrene‐1,4‐dione (4), 5,7,8‐trimethyl‐2‐(prop‐2‐enyl)phenanthrene‐1,4‐dione (17), and 3‐hydroxy‐2‐methylphenanthrene‐1,4‐dione (42). The quinones 1 and 3 proved to be identical with the recently isolated plectranthons A and C. Compounds 2, 31, and 32 exhibited the same UV/VIS, IR, 1H‐NMR and mass spectra as natural plectranthon B, but had different melting points. This might be due either to crystal modifications or to diastereoisomerism caused by the helical structure of the phenanthrene‐1,4‐dione skeleton. The spectral data of synthetic 4 were not compatible with those of natural plectranthon D for which structure 4 had been proposed based mainly on 1H‐NMR arguments concerning the chemical shifts of HC(9) and HC(10) in 1–3. Extensive 1H‐NMR investigations have now revealed that the currently stated assignments of the HC(9)/ HC(10) AB system have to be reversed for highly substituted phenanthrene‐1,4‐diones: in the model compounds 2‐methylphenanthrene‐1,4‐dione (41) and 2, HC(10) resonates al lower field as expected (peri‐position), whereas in the highly substituted congeners 1, 2, 3, 31, and 32, HC(9) is shifted paramagnetically, a fact which had lead to the erroneous assignment of structure 4 for natural plectranthon D.
Dehydration of Alkanones by Bare FeO+ Involves the ω/(ω − 1) Positions: Exclusion of Iron Carbenes as Intermediates. Preliminary Communication
Authors: Schröder Detlef , Eller Karsten , Schwarz Helmut
Published: December 2004

Fourier‐transform ion‐cyclotron‐resonance (FTICR) mass spectrometry has been used to uncover the mechanisms by which FeO+ dehydrates heptan‐4‐one (5a) and nonan‐5‐one (6a) in the gas phase. The study of isotopomeric ketones provides evidence that H2O loss is not due to a 1,1‐elimination, thus ruling out the intermediacy of high‐valent iron‐carbene species. Rather, H2O is generated in a formal 1,2‐elimination involving the ω/ω − 1 positions of the alkyl chain (‘remote CH bond activation’). In the consecutive alkene/H2O elimination, the olefins (ethylene from 5a and propene from 6a) originate from the terminal part of one alkyl chain, and the H‐atom is transferred to the FeO+ moiety in the course of this process, builds up together with an H‐atom from the ω/ω‐1 position of the other alkyl chain the H2O molecule. In either case, the O‐atom of H2O is provided by the FeO+ species.
Coralloidolide F, the First Example of a 2,6‐Cyclized Cembranolide: Isolation from the Mediterranean Alcyonacean Coral Alcyonium coralloides
Authors: D'Ambrosio Michele , Guerriero Antonio , Pietra Francesco
Published: December 2004

The Mediterranean alcyonacean Alcyonium ( = Parerythropodium) coralloides (Pallas, 1766) is shown here to contain coralloidolide F ( = (+)‐(3a‐R*, 7R*, 8R*, 9R*, 12R*, 12aS*)‐8,9‐epoxy‐1,3a,6,7,8,9,10,11,12,12a‐decahydro‐3a‐hydroxy‐12‐isopropenyl‐2,5‐dimethyl‐1‐oxocyclopfintacycloundecene‐9,7‐carbolactone; (+)‐2), the first example of a 2,6‐cyclized cembranolide. Structural assignments are mainly based on ID and 2D NMR and MS data.
Photorearrangement of 4,4‐Dimethylcyclohex‐2‐enones with Alkyl or Fluoro Substituents at C(5) and C(6): In Search of the Mechanism
Authors: Cruciani Giuliano , Margaretha Paul
Published: December 2004

The photorearrangement of cyclohex‐2‐enones 4a‐h to bicyclo[3.1.0]hexan‐2‐ones 5 and cyclopent‐2‐enones 6 (λ = 350 nm, MeCN) was investigated. Both the quantum yield (Φ−4 = 0.004– 0.024) and the product ratio (5/6 = 65:35–31:69) vary only over a rather small range, indicating the rearrangement to be relatively insensitive to substituents on C(5) or C(6). Compounds 4b, 4c, and 4g with just one alkyl group at either C(6) or C(5) rearrange selectively to the diastereoisomer 5 with alkyl group and three‐membered ring in trans‐configuration, while 6‐fluorocyclohex‐2‐enones 4d and 4f afford mixtures of diastereoisomeric bicyclohexanones. Mechanistic conclusions regarding an intermediate trimethylene biradical are presented.
Photochemical reactions. 152nd Communication. Photochemistry of acylsilanes; photolysis and thermolysis of cyclopropyl silyl ketones
Authors: Scheller Markus E. , Frei Bruno
Published: December 2004

The photolysis and thermolysis of the Cyclopropyl silyl ketones 3, 4, and 5 are described. On n,π* excitation, the silyl ketones 3 and 4 undergo a Norrish‐type‐II reaction involving γ‐H abstraction, cyclopropyl ring cleavage followed by retro‐enolization to the acylsilanes 6 and (E/Z)‐12, respectively. As a common product of 3 and 4, the dihydrofuran 7 is formed via the alternative C(α)‐C(β) cleavage of the cyclopropyl moiety. Compounds 6, 7, and (E/Z)‐12 are new types of acylsilane photoproducts. The irradiation of acylsilane 5 gave the analogous dihydrofuran 15 as the only product. On photolysis of 3 and 4, products 8A + B and 13A + B, derived from a siloxy carbene intermediate, were found as well. On thermolysis of 3 and 4, the acylsilanes 6 (80%), and (E)‐12 (33%) and (Z)‐12 (34%), respectively, are formed as the only products. Their formation may occur via a [1, 5] sigmatropic H‐shift. The thermolysis of 5 gave the diene 16 whose formation can be explained by insertion of a siloxycarbene into the neighboring cyclopropane leading to the cyclobutene 28 as thermally unstable intermediate.
Totalsynthese von natülichem α‐Tocopherol. 5. Mitteilung. Asymmetrische Alkylierung und asymmetrische Epoxidierung als Methoden zur Einführung der (R)‐Konfiguration an C(2) des Chroman‐Systems
Authors: Hübscher Josef , Barrier Richard
Published: December 2004

Total Synthesis of Naturally Occurring α‐Tocopherol. Asymmetric Alkylation and Asymmetric Epoxidation as Means to Introduce (R)‐Configuration at C(2) of the Chroman Moiety

Based on the reductive, stereospecific ring closure of (2R,4′R,8′R)‐α‐Tocophcrylquinone′ or corresponding analogues with a short, functionalized side chain (B, Scheme 1) to 1 resp. the chroman system of 1 (C), two different approaches for the introduction of the required tertiary methyl‐substituted alcohol structure in the side chain of the aromatic precursors (A, Scheme 1) were developed. The first approach uses asymmetric alkylation in three different versions featuring (a) diastereoselective steering with chiral auxiliaries I‐IV (Scheme 2) attached as esters to a‐keto acids, (b) intermediate transfer of chirality in an ester enolate (from 18, Scheme 4) derived from an optically active α‐hydroxy acid, (c) enantioselective alkylation of phytenal (20) and subsequent ring closure with chirality transfer (Schemes 5–7). The second approach is based on the asymmetric epoxidation of β‐metallylalcohol (Sharpless epoxidation), the corresponding epoxyalcohol being converted in situ to the (S)‐or (R)‐chlorodiol (S)‐and (R)‐29, respectively, for isolation (Schemes 8 and 9). Nucleophilic epoxide opening with a (3R 7R)‐3,7,11‐trimethyldodecyl (C15**) and an ArCH2 unit in appropriate sequence is used to assemble the C‐framework of the target molecule via corresponding epoxide intermediates from either chlorodiol. Combined with the use of the methoxymethyl‐ether function for protection of the hydroquinone system, the epoxide approach provides a short route to 1 (Scheme 10).
Die Synthese des Labdanditerpenes Erigerol und analoger Verbindungen
Authors: Kienzle Frank , Stadlwieser Josef , Rank Werner , Schonholzer Peter
Published: December 2004

The Synthesis of the Labdane Diterpenoid Erigerol and of Analogous Compounds

The synthesis of Erigerol (1) and of analogous compounds in a 23‐step sequence is described. The various difficulties of the synthesis and several blind alleys that have been followed are discussed.
Synthesis and Properties of a New Dihydroflavin: Reduction of a Flavinium Salt by Borocyanohydride
Authors: Szczesna Violetta , Müller Franz , Vervoort Jacques
Published: December 2004

Reduction of 6 by borocyanohydride yielded the new dihydroflavin 7. The intermediate product 8 could only be observed in solution by 1H‐NMR. The chemical and physical properties of 7 are reported. UV/VIS, 1H‐ and 13C‐NMR, and luminescence techniques were used.
Regio‐, Diastereo‐, and Enantioselective Synthesis of Vicinal Diols via α‐Silyl Ketones
Authors: Enders Dieter , Nakai Shiro
Published: December 2004

A new versatile and efficient regio‐, diastereo‐, and enantioselective synthesis of vicinal diols s‐trans‐4, s‐trans‐5, and s‐cis‐4 is described. Symmetrical ketones are converted into their SAMP‐or RAMP‐hydrazones which are then silylated with (isopropyloxy)dimethylsilyl chloride, followed by ozonolysis to afford the α‐silyl ketones (R)‐2 of high enantiomeric purity (ee 90– ≥ 98%). On the other hand, methyl ketones, after conversion into the corresponding (−)–(S)‐1‐amino‐2‐(methoxymethyl) pyrrolidine (SAMP) hydrazones, are silylated and then alkylated with RI to afford unsymmetrical α‐silyl ketones (S)‐3 of high enantiomeric purity (ee 90‐ ≥ 98%). The reduction of the above obtained α‐silyl ketones with L‐Selectride, followed by oxidative cleavage of the CSi bond gives rise to s‐trans‐4, s‐trans‐5, and s‐cis‐4 with high diastereoselectivity (de 95‐ ≥ 98%) and without racemization (ee ≥ 90– ≥ 98%).
Probing the Anomeric Effect in OCN Systems Theory vs. Experiment: MO‐ab initio Calculations and a Structural‐Statistical Analysis
Authors: Senderowitz Hanoch , Aped Pinchas , Fuchs Benzion
Published: December 2004

A combined computational (MO ab initio) and structural‐statistical study of molecules containing the OCN moiety is presented. Aminomethanol, the simplest member of this series, was computed using GAUSSIAN‐82 with the 3‐21G and 6‐31G* basis sets and with complete geometry optimization, as well as with MP3//6‐31G*. A set of carefully selected molecules containing the OCN unit was retrieved from the Cambridge Structural Database (CSD), and its structural parameters were analyzed according to an established procedure. Comparison between experimental and computational data was thus made possible. Results are consistent with the co‐existence of two unequal anomeric effects in this system: a strong nN‐σ*CO anomeric interaction, and a weak nπO‐σ*CN one. The ability of the two basis sets to reproduce the energies and structural characteristics of the stereoelectronic effects is assessed, including the significance of using polarization functions and the inclusion of correlation energy.
Asymmetric Diels‐Alder Cycloadditions with C2‐Symmetrical Chiral Carbamoylnitroso Dienophiles
Authors: Defoin Albert , Brouillard‐Poichet Agnès , Streith Jacques
Published: December 2004

The C2‐symmetrical chiral pyrrolidines 2 and 3 are of opposite helicity. The corresponding N‐acylnitroso dienophiles 6 and 7 react in good yield with cyclohexadiene, leading thereby with excellent diastereoisomeric excess to the expected Diels‐Alder cycloadducts (see Scheme). The [2.2.2] bicyclic moieties of the major diastereoisomers 9 and 11 proved to be of opposite configuration, as expected. Their configuration is best explained by assuming the acylnitroso dienophile to be in the s‐cis conformation in the transition state, the approach of the diene being endo (see Fig.).
Ammodoremin, an Epimeric Mixture of Prenylated Chromandiones from Ammoniacum
Authors: Appendino Giovanni , Nano Gian Mario , Viterbo Davide , De Munno Giovanni , Cisero Marco , Palmisano Giovanni , Aragno Manuela
Published: December 2004

From the gun resin Ammoniacum, an epimeric mixture 2a/3a of highly functionalized prenylated chromandiones was isolated. Their structure was established by spectral data and single‐crystal X‐ray analysis. The compounds were isolated as acetates 2b/3b, and these derivatives showed in vivo haemorrhagic activity.
Syntheses and Crystal Structures of 4,5‐Dihydro‐2‐(2′‐hydroxyphenyl)oxazole‐Containing Metal Complexes
Authors: Bolm Carsten , Weickhardt Konrad , Zehnder Margareta , Glasmacher Dorothea
Published: December 2004

The synthesis of the complexes 3 of various metals ligated to chiral 4,5‐dihydro‐2‐(2′‐oxidophenyl‐ϰO)oxazoles‐ϰN is described (Scheme). Three of them, i.e. 3a, 3e, and 3f containing CuII, ZnII and NiII, respectively, were analyzed by X‐ray diffraction studies. A series of CuII complexes (6a–d) with differently substituted dihydrooxazoles have been synthesized.
Synthesis and X‐Ray Crystal Structure of an Optically Pure Tripodal C3‐Symmetric Tritertiary Phosphine Bearing Chirality on Phosphorus
Authors: Ward Thomas R. , Venanzi Luigi M. , Albinati Alberto , Lianza Francesca , Gerfin Tobias , Gramlich Volker , Tombo Gerardo M. Ramos
Published: December 2004

The preparation of the optically pure tritertiary phosphine (RRR)‐MeSi(CH2P(t‐Bu)Ph)3 (2) is reported. The route followed involves deprotonation of optically pure (R)‐P(BH3)Me(t‐Bu)PH (2) the reaction of the resulting carbanion with MeSiCl3, followed by removal with morpholine of the BH3‐protecting groups from the triertiary phosphine‐borane 3. The latter's X‐ray crystal structure and that of [Rh(NBD)((RRR)‐1]TOf)(4), are also rported. Furthermore, it is shown that the separation of the racemic phosphine‐borane 2 can be conveniently carried out using medium‐pressure liquid chromatgrapy with cellulose‐riacetate as a chiral stationary phase.
Ringerweiterung von 1,2‐Thiazol‐3(2H)‐on‐1,1‐dioxiden und 3‐Amino‐2H‐azirinen zu 4H‐1,2,5‐Thiadiazocin‐6‐on‐1,1‐dioxiden
Authors: Rahm Annette , Linden Anthony , Vincent Beverly R. , Heimgartner Heinz , Mühlstädt Manfred , Schulze Bärbel
Published: December 2004

Ring Enlargement of 1,2‐Thiazol‐3(2H)‐one‐1,1‐dioxides and 3‐Amino‐2H‐azirines to 4H‐1,2,5‐Thiadiazocin‐6‐one‐1,1‐dioxides

Reaction of 3‐amino‐2H‐azirines 2 with the 1,1‐dioxides 4 and 7 of 1,2‐thiazol‐3(2H)‐ones and 1,2‐thiazoli‐din‐3‐ones, respectively, in i‐PrOH at room temperature leads to 4H‐1,2,5‐thiadiazocin‐6(5H)‐one‐1,1‐dioxides 5 (Scheme 2, Table) and the corresponding 7,8‐dihydro derivatives 8 (Scheme 4), respectively. The structure of some of the new 8‐membered heterocycles as well as the structure of the minor by‐product 6 (Scheme 3) have been established by X‐ray crystallography (Chapt. 4). The proposed reaction mechanism for the ring expansion to 5 and 8 (Scheme 2) is in accordance with previously published results of reactions of 2 and NH‐acidic heterocycles and is further supported by the results of the reaction of 4a and the (1‐15N)‐labelled aminoazirine 2a*.
Structure and reactivity of xanthocorrinoids. Part V. Formation of trans‐diol derivatives of 5,6‐dihydrocobyrinic acid from xanthocorrinoids under acidic conditions
Authors: Holxe Gerhard , Jenny Titus A. , Nesvadba Petr , Gossauer Albert , Ernst Ludger , Keller Walter , Kratky Christoph
Published: December 2004

On treatment with H2SO4/MeOH, epimerization of hexamethyl cis‐5,6‐dihydroxycobyrinate c,8‐lactam (3) takes place quantitatively at C(6), yielding the corresponding trans‐diol 4. The corresponding lactone 7, whose structure has been established by X‐ray analysis, is obtained from xanthocorrinoids 5 and 6 under similar conditions.
Reactions of Sulfinylated Radicals. Stereoselectivity in Six‐Membered Rings
Authors: Rehaud Philippe
Published: December 2004

The allylation and deuteration of six‐membered cyclic sulfinylated radicals were investigated. For this purpose, radicals with the predefined conformations I and II were generated from 2‐(phenylselenenyl)thiacyclo‐hexane‐1‐oxide derivatives 7–10 (Scheme). Steric effects were insufficient to account for all the observed selectivities. The participation of stereoelectronic effects are envisaged to explain the stereoselective axial deuteration of type‐II radicals.
Cuprous complexes and dioxygen. Part 11. Concomitant one‐ and two‐electron reduction of O2 by the Cu ion
Authors: Mi Li , Zuberbühler Andreas D.
Published: December 2004

The autoxidation of CuI in aqueous MeCN has been studied using a Clark oxygen electrode in the presence and absence of Cu11. The reaction is inhibited by Cu11 in the pH range of 0.5 to 5.0, reaching a lower limiting value at the highest concentrations. The reaction order changes from 1 to 2 with respect to CuI under the influence of Cu2+ ion. Detailed kinetics analysis of a total of 275 measurements has shown that an unstable primary adduct CuO+2 decomoses to give .O or HO, depnding on pH, and also reacts directly with a second Cu+ ion, avoiding one‐electrton reduction of O2 by this path. Reaction of HO is faster with CuI than with Cu11 by a factor of 20, and single‐electron transfer within CuO+2 to Cu2+ and .O predominates over reaction with a second copper ion for [CuItot] < 2. 10−3M in the absence of Cu2+. The most likely value for the reaction of .O with CuI is 5.3 · 108 M−1S−1, but even this high rate constant is at the limit of significance. All secondary reactions followinfg the initial formation of CuO+2 are shown to be very fast, a fact that should be properly considered in the discussion of mechanisms of copper‐catalyzed oxidations and oxygenations.
A Reduction Catalyst Powered by Its Own 10‐Electron Battery: Synthesis and properties of a pentaviologen‐linked corrinatocobalt complex
Authors: Steiger Beat , Walder Lorenz
Published: December 2004

The synthesis and properties of the molecular reduction device 7b (CoII–V) consisting of a reduction catalyst (a derivative of vitamin B12, CoII) and a covalently linked 10‐electron reservoir (five viologen units, V++) is described. The five viologen subunits were introduced at C(2) and C(3) of the side chains c and g and b, e and f, respectively, of an appropriate derivative of heptamethyl cob(III)yrinate by N‐alkylation of 1‐methyl‐4,4′‐bipyridinium iodide (see Scheme). The pentaviologen‐linked corrinatocobalt(II) complex 7b behaves as a molecular electron trap with respect to the CoIII/CoII redox couple. The phenomenon is related to the structural and thermodynamic relation of the corrin and viologen subunits in 7b, i.e. the relative redoc energies and the spherical inner‐outer arrangement of the types of redox systems. When completely reduced to CoI–V, 7b exhibits multiple reductive elimination of trans‐1,2‐dibromocyclohexane to cyclohexene under concomitant oxidation to CoII–V. Rate measurements indicate that the reduction occurs via CoI which is regenerated by intramolecular electron transfer from the periphery of the molecule, i.e. by V0 and V++.