bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transfer Mechanism of Ionic Drugs: Piroxicam as an agent facilitating proton transfer
Authors: Reymond Frédéric , Steyaert Guillaume , Pagliara Alessandra , Carrupt Pierre‐Alain , Testa Bernard , Girault Hubert 
Published: December 2004

AbstractFacilitated proton transfer may be of potential significance in pharmacokinetic and pharmacodynamic processes. Here, we show that the NSAID piroxicam and its N‐and O‐methylated derivatives act as ionophores for proton transfer across the H2O/1,2‐dichloroethane interface. Investigations by cyclic voltammetry showed that the proton transfer occurs by interfacial protonation of the ionophore. The dissociation constants of the three compounds in the organic phase were calculated by Matsuda's theory. With this particular transfer mechanism, the present study exemplifies how electrochemistry at a liquid/liquid interface can be applied to calculate the fundamental thermodynamic parameters related to the pharmacokinetic behavior of ionic drugs.
Synthesis and Enzymatic Evaluation of Substrates and Inhibitors of β‐Glucuronidases
Authors: Hoos Roland , Huixin Jiang , Vasella Andrea , Weiss Patrick 
Published: December 2004

AbstractThe phosphono and the tetrazolyl analogues 4 and 5 of 4‐methylumbelliferyl β‐D‐glucuronide (=(4‐methyl‐2‐oxo‐2H‐1‐benzopyran‐7‐yl β‐D‐glucopyranosid)uronic acid; 6) were synthesized and evaluated as substrates of β‐glucuronidases. Similarly, the phenylcarbamate 7 and its phosphono analogue 8 were prepared and evaluated as inhibitors. To examine the diastereoselectivity of the phosphorylation, we also synthesized the protected L‐ido‐D‐gluco‐, and D‐galacto‐configurated phospha‐glycopyranuronates 12, 13, 21, 22, 34 and 35. Two strategies were followed. In the first one, the glucuronic acid 19 was decarboxylated to 11 and further transformed, via 20, into the trichloroacetimidate 10 (Scheme 2). Phosphorylation of 10 with (MeO)3P yielded the diastereoisomers 12 and 13, the diastereoselectivity depending on the solvent. In MeCN, 12 and 13 were obtained in a ratio of 1:1, while in non‐participating solvents the L‐ido 12 was by far the major diastereoisomer. The acetate 11 was inert to (MeO)3P, but reacted with (PhO)3P to the anomeric mixture 21/22, in keeping with a stabilizing 1,3‐interaction in the intermediate phosphonium salt. Similarly, the phospha‐galacturonates 34 and 35 were prepared from the galactoside 23 via the enol ether 26, the lactone 27, and the acetates 28/29 that were also transformed into the trichloroacetimidate 33 (Scheme 3). In the second, higher‐yielding strategy, phosphorylation of the pentodialdehyde 39 to 40/41 was followed by hydrolysis and acetylation to the phospha‐glucuronates 43/44 (Scheme 4). Transesterification to 45/46, selective deacetylation to 48/49, and formation of the trichloroacetimidates 50/51 were followed by glycosidation and deprotection to 4. The tetrazole 5 was prepared from the lactones 54/55 via the N‐benzylamides 57/58 that were treated with TfN3 to give the N‐benzyltetrazoles 59/60 (Scheme 4). These were transformed into the trichloroacetimidates 63/64, glycosylated to 65, and deprotected. The O‐carbamoylhydroximo‐lactone 7 derived from the glucuronate 67/68, and the phosphonate analogue 8 were prepared by established methods. The phosphonate 4 is slowly hydrolyzed by the E. coli β‐glucuronidase, but neither 4 nor the tetrazole 5 are affected by the bovine liver β‐glucuronidase (Table 4). The phenylcarbamate 7 of D‐glucarhydroximo‐1,5‐lactone, but not its phosphonate analogue 8, is an inhibitor (KI = 8 m̈M) of the E. coli β‐glucuronidase. The bovine liver β‐glucuronidase is inhibited strongly by 7 (IC50 = 0.2 m̈M) and weakly by 8 (IC50 = 2mM).
Synthesis and Characterization of Non‐standard Nucleosides and Nucleotides Bearing the Acceptor‐Donor‐Donor Pyrimidine Analog 6‐Amino‐3‐methylpyrazin‐2(1H)‐one
Authors: Voegel Johannes J. , Benner Steven A. 
Published: December 2004

Abstract6‐Aminopyrazin‐2(1H)‐one, when incorporated as a pyrimidine‐base analog into an oligonucleotide chain, presents a H‐bond acceptor‐donor‐donor pattern to a complementary purine analog. When paired with the corresponding donor‐acceptor‐acceptor purine in oligonucleotides, the heterocycle selectively contributes to the stability of the duplex, presumably by forming a base pair of Watson‐Crick geometry joined by a non‐standard H‐bonding pattern. Aspects of the nucleoside chemistry, including syntheses of the β‐furanosyl ribonucleoside 1, the ribonucleoside triphosphate 2 and the ribonucleoside bisphosphate 3 of 6‐aminopyrazin‐2(1H)‐one are reported here. In aqueous solution, the ribonucleoside 1 was found to undergo acid‐ and base‐catalyzed rearrangement with an apparent half‐life of ca. 63 h at neutral pH and 30°. The rearrangement appears to be specific acid‐ and base‐catalyzed. The thermodynamically most stable compound formed during this rearrangement reaction was isolated by HPLC and shown to be the β‐pyranosyl form 4 of the 6‐aminopyrazin‐2(1H)‐one nucleoside in its 4C1 chair conformation. This reactivity of 1 under physiological conditions may explain why Nature does not use this particular heterocyclic system to implement an acceptor‐donor‐donor H‐bonding pattern in the genetic alphabet.
Synthesis, Molecular Recognition, and Enzymology of Oligonucleotides Containing the Non‐standard Base Pair between 5‐Aza‐7‐deazaisoguanine and 6‐Amino‐3‐methylpyrazin‐2(1H)‐one, a Donor‐Acceptor‐Acceptor Purine Analog and an Acceptor‐Donor‐Donor Pyrimidine Analog
Authors: Voegel Johannes J. , Benner Steven A. 
Published: December 2004

AbstractA 6‐aminopyrazin‐2(1H)‐one (pyADD), when incorporated as a pyrimidine‐base analog into an oligonucleotide chain, presents a H‐bond acceptor‐donor‐donor pattern to 5‐aza‐7‐deazaisoguanine (puDAA), the complementrary donor‐acceptor‐acceptor purine analog. Reported here are the syntheses of the phosphoramidite of the 2′‐deoxyribonucleoside bearing the puDAA base, oligonucleotides containing this nucleoside unit, the enzyme‐assisted synthesis of oligoribonucleotides containing the pyADD ribonucleoside, and the molecular‐recognition properties of this non‐standard base pair in an oligonucleotide context. A series of melting experiments suggests that the pyADD · puDAA base pair contributes to the relative stability of a duplex structure approximately the same as an A · T base pair, and significantly more than mismatches between these non‐standard bases and certain standard nucleobases. The pyADD nucleoside bisphosphate is accepted by T4 RNA ligase, but the triphosphate of the pyADD nucleoside was not incorported by T7 RNA polymerase opposite the puDAA nucleobase in a template. Oligonucleotides containing the pyADD base slowly undergo a reversible first‐order reaction, presumably an epimerization process to give the α‐D‐anomer. These experiments provide the tools for laboratory‐based use of the pyADD · puDAA base pair as a component of an oligonucleotide‐like molecular‐recognition system based on an expanded genetic alphabet.
The Molecular and Crystal Structure of the Glycopeptide A‐40926 Aglycone
Authors: Schäfer Martina , Pohl Ehmke , Schmidt‐Bäse Karen , Sheldrick George M. , Hermann Rolf , Malabarba Adriano , Nebuloni Marino , Pelizzi Giancarlo 
Published: December 2004

AbstractThe crystal structure of a glycopeptide antibiotic A–40926 aglycone was investigated by X‐ray analysis at −120°. A‐40926 crystallises in the orthorhombic space group P212121 with two monomers in the asymmetric unit, a = 21.774(4), b = 28.603(7), c = 29.757(4) Å. ‘Conventional’ direct methods approach failed to solve the structure, but a novel iterative real/reciprocal space procedure was successful. Refinement against 11248 F2 data led to R1 = 13.3% for 6770 F > 4σ (F). The two monomers of A‐40926 have similar conformations and are bound by antiparallel H‐bonds to form a ‘chain’ structure of connecting dimers. The antibiotic molecule possesses a ‘binding pocket’ for the C‐terminal carboxy group of the cell‐wall protein, which is consisten with suggestions based on NMR data and the recently reported crystal structure of ureido‐balhimycin. In A‐40926 the monomers are polymerically linked by H‐bonds, quite unlike the tight dimer formation observed in ureido‐balhimycin.
Model Studies for the Coenzyme‐B12‐Catalyzed Methylmalonyl→Succinyl Rearrangement. The Importance of Hydrophobic Peripheral Associations
Authors: Darbre Tamis , Keese Reinhart , Siljegovic Vuk , Wolleb‐Gygi Annemarie 
Published: December 2004

AbstractThe interaction between a vitamin B12 derivative containing a peripheral C18 alkyl chain (see 1a) and a (methyl)thiomalonate substrate bearing alkyl chains of various length at the thioester group (see 5) was investigated. A catalytic cycle was established for the methylmalonyl→succinyl rearrangement by using electrochemistry and photolysis (see Scheme 3). Increased yields of the succinate relative to the reduction product were obtained (2:3 ratio), when the reaction was run in MeOH/H2O, and when both the substrate and the catalyst had an octadecyl substituent capable of hydrophobic interactions.
5,5′‐Bi‐5H‐cyclopenta[2,1‐b;3,4‐b′]dipridinylidene, a New Bridging Ligand for Metal Complexes. Preliminary Communication
Authors: Riklin Marianne , von Zelewsky Alex 
Published: December 2004

Abstract5,5′‐Bi‐5H‐cyclopenta[2,1‐b;3,4‐b′]dipyridinylidene(1) was synthesized in three steps from 9,10‐phenanthroline and characterized by UV/VIS and NMR spectroscopy, mass spectrometry, and cyclic voltammetry. Its ability to act as a bridging ligand is demonstrated by the synthesis of the complexes [Ru(bpy)2(1)](PF6)2 (6) and [{Ru(bpy)2}2(1)](PF6)4 (7) (bpy = 2,2′‐bipyridine).
Total Synthesis of Cyclothialidine
Authors: Götschi Erwin , Jenny Christian‐Johannes , Reindl Peter , Ricklin Fabienne 
Published: December 2004

AbstractA total synthesis of cyclothialidine (1), a new DNA gyrase inhibitor isolated from Streptomyces filipinensis, is described. The synthetic concept was tested by preparing the lactone 13 (Scheme 2) which contains the characteristic bicyclic core entity of 1. Key features of the synthesis of 1 are: preparation of 3,5‐dihydroxy‐2,6‐dimethylbenzoic acid (23) from 3,5‐dihydroxybenzoic acid (19) by two consecutive Mannich aminomethylation/hydrogenation sequences; benzylic N‐bromosuccinimide bromination of an ester derivative 25 thereof and its subsequent coupling with Boc‐Ser‐Cys‐OMe (11); cyclization of the ω‐hydroxy acid 29 29 to the 12‐membered lactone 30 using preferably Mitsunobu conditions; completion of the peptidic side chains of 1 using Boc strategy (Scheme 4). Optically pure cis‐N‐(tert‐butoxycarbonyl)‐3‐hydroxy‐L‐proline ((–)‐14) was obtained by resolution of the racemate via an efficient reaction sequence containing a lipase‐catalyzed enantiospecific acetate hydrolysis (Scheme 3). The structure of natural 1 was confirmed by comparison with the synthetic material. The synthetic route described provides also easy access to analogues of 1, e.g., via the intermediate 30.
Donor/Acceptor‐Substituted Tetraethynylethenes: Systematic Assembly of Molecules for Use as Advanced Materials
Authors: Tykwinski Rik R. , Schreiber Martin , Carlón Raquel Pérez , Diederich François , Gramlich Volker 
Published: December 2004

AbstractA comprehensive series of tetraethynylethenes (= 3,4‐diethynylhex‐3‐ene‐1,5‐diynes, TEEs) bearing electrondonating (p‐methoxyphenyl or p‐aminophenyl) and/or electron‐accepting (p‐nitrophenyl) groups was prepared via [Pd]‐catalyzed Sonogashira cross‐coupling reactions. The electronic and photonic properties of these molecules were investigated with a special emphasis on the effects caused by degree and pattern of donor/acceptor substitution around the central TEE core. This analysis showed that intramolecular donor‐acceptor interactions, as evidenced by a long‐wavelength charge‐transfer band, are considerably more effective in TEEs 44 and 46, with trans and cis, linearly‐conjugated electronic pathways between donor and acceptor, than in 11, with a geminal, cross‐conjugated electronic pathway. UV/VIS Spectroscopy revealed a steady bathochromic shift of the longest‐wavelength absorption band (λmax) as the number of donor‐acceptor conjugation paths increased upon changing from bis‐arylated (11, 44, and 46) to tetrakis‐arylated (14, 31, and 35) TEEs. The position of the longest‐wavelength absorption was also found to be strongly dependent on the nature of the N‐substituents in the R2NC6H4‐donor groups. Electronic emission spectroscopic investigations demonstrated a considerable solvent dependency of the fluorescence of donor‐acceptor‐substituted TEEs such as 11 or 44, in agreement with the presence of highly polarized excited states in these molecules. Correspondingly, fluorescence spectra of TEEs bearing only donor or acceptor substituents showed little solvent dependency. The large majority of the donor/acceptor‐substituted TEEs are thermally and environmentally stable molecules. They can be stored for months as solids in the air at room temperature, and many decompose only upon heating to temperatures above 200°. X‐Ray analysis showed the conjugated C‐atom scaffolds of 44, 46, and 67 to be essentially planar, whereas the aryl substituents in 28 and 30 are rotated out of the plane of the TEE core by varying degrees.
Long‐Distance Effect on One‐Bond CC Scalar couplings upon introduction of a double bond in bicyclic systems
Authors: Jones Graeme R. , Caldarelli Stefano , Vogel Pierre 
Published: December 2004

AbstractAnomalous variations of one‐bond CC scalar coupling constants are observed in going from trinorbornane‐to trinorbornene‐like structures. Most notably, a 10‐Hz increase is observed in the coupling constant involving the C‐atoms of the ethano branch facing the CC bond. An effect of about half the size is characteristic of higher homologues (bicyclo[2.2.2]octenes), but no such effect is observed for monocyclic molecules.
Models for the Active Center of Pterin‐Containing Molybdenum Enzymes: Crystal structure of a molybdenum complex with sulfur and pterin ligands
Authors: Fischer Berthold , Schmalle Helmut W. , Baumgartner Markus R. , Viscontini Max 
Published: December 2004

AbstractThe first crystal structure of a molybdenum complex 9 with a hydrogenated pterin and a sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex 9 was synthesized through a redox reaction of [MoVIO2 (LN‐S2)] (8; LN‐S2 = pyridine‐2, 6‐bis(methanethiolato)) with 5, 6, 7, 8‐tetrahydropterin (7). 2 HCl (H4Ptr.2 HCl). The complex crystallizes, with a non‐coordinating Cl‐atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensions a = 22.900(5), b = 10.716(2), c = 17.551(4) Å, β = 120.36(3)°, and Z = 8. We interpret 9 as [MoIVO(LN‐S2)(H+‐q‐H2Ptr)]Cl (q = quinonoid; H2Ptr = dihydropterin), i.e., a MoIV monooxo center coordinated by a pyridine‐2, 6‐bis(methanethiolato) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S‐coordination. The slightly H2O‐soluble complex 9 reacts with the natural enzyme substrate DMSO very slowly, possibly due to the lack of easily dissociable ligands at the metal center.
6‐Azabicyclo[3.1.0]hex‐30‐en‐2‐ol Derivative, photochemically generated building blocks for bicyclic β‐lactams
Authors: Glarner Fabrice , Thornton Steven R. , Schärer Daniel , Bernardinelli Gérald , Burger Ulrich 
Published: December 2004

AbstractThe title compounds 4 are obtained by photolysis of simple N‐alkylpyridinium salts in H2O or alcohol. On reaction with [Fe2(CO)9] in THF, 4 gives bicyclic tricarbonyliron complexes 13a–d, which on oxidative decomplexation with ceric ammonium nitrate afford cis‐fused cyclopenteno‐β‐lactams 15a–d.
Metal Complexes with Macrocyclic Ligands. Part XLIII. Tetraazamacrocyclic nickel(II) and copper(II) complexes with aliphatic methylthio‐ and methoxy‐substituted pendant chains
Authors: Schmid Claudio L. , Neuburger Markus , Zehnder Margareta , Kaden Thomas A. , Bujno Krzysztof , Bilewicz Renata 
Published: December 2004

AbstractThe 14‐membered tetraazamacrocyclic Ni2+ and Cu2+ complexes of 4 (1, 4, 8‐trimethyl‐11‐[(2‐methylthio)ethyl]‐1, 4, 8, 11‐tetraazacyclotetradecane), 5. (1, 4‐dimethyl‐8, 11‐bis[2‐(methylthio)ethyl]‐l, 4, 8, 11‐tetraazacyclotetradecane), and 7 (1, 4, 8, ll‐tetrakis[2‐(methylthio)ethyl]‐1, 4, 8, 11‐tetraazacyclotetradecane), with pne, two, and four methylthio‐substituted pendant chains, respectively, and the Ni2+ complex of 6 (1, 4‐dimethyl‐8, 11‐bis (2‐methoxyethyl)‐1, 4, 8, 11‐tetraazacyclotetradecane), with two methoxy‐substituted pendant chains, were synthesized and their chemistry studied with regard to modelling F430. Solution spectra in H2O, MeCN, and DMF indicate participation of the side chain in metal coordination when the donor group is a thioether, whereas no coordination with the metal ion is observed with the ether group. Similarly the X‐ray structures of the thioether‐containing compounds [Ni(5)](ClO4)2, [Cu(5)](ClO4)2, and [Cu(7)](ClO4)2 show a coordination number of 5, whereas that of [Ni(6)](ClO4)2 with ether pendant chains, shows a coordination number of 4. Cyclic voltammetry of these complexes in MeCN reveals that Ni2+ is reversibly reduced to Ni+ between −0.64 and −0.77 V vs. SCE, the potential being influenced by the nature and number of the pendant chains. At more negative potentials, the thioether is cleaved, whereby a thiol is formed; the thiol is then oxidized at ca. + 0.8 V vs. SCE, when a glassy carbon electrode is used, or at ca. 0 V vs. SCE at a dropping Hg electrode. No cleavage of the ether bond in [Ni(6)](ClO4)2 is observed under similar conditions.
Palladium‐Catalysed Intramolecular Cyclisations of Olefinic Propargylic Carbonates and application to the diastereoselective synthesis of enantiomerically pure (−)‐α‐thujone
Authors: Oppolzer Wolfgang , Pimm Austen , Stammen Blanda , Hume W. Ewan 
Published: December 2004

AbstractIntramolecular [Pd2(dba)3]/tri(2‐furyl)phosphine‐catalysed (dba = dibenzylideneacetone, PhCHCHCOCHCHPh) cyclisations of olefinic propargylic carbonates I provided alk‐1‐enyl‐(3‐aza)bicyclo[3.1.0]‐hexanes VIII in good yields. A palladium cascade sequence I → II → III → IV → VII → VIII is proposed. Furthermore, chiral propargylic carbonates such as 23, 24 and 25 allowed diastereoselective formation of bicyclo[3.1.0]hexanes 29, 30 and 31, respectively. The first diastereoselective synthesis of the monoterpene, (−)‐α‐thujone 40 illustrates the potential of the method.
Rogioldiol A, a new obtusane diterpene, and rogiolal, a degraded derivative, of the red seaweed Laurencia microcladia from II rogiolo along the coast of tuscany: A Synergism in Structural Elucidation
Authors: Guella Graziano , Pietra Francesco , Marchetti Fabio 
Published: December 2004

AbstractThe structure of rogioldiol A ((−)‐1), isolated from the red seaweed Laurencia microcladia, was determined. Employing the exciton‐coupling technique for rogioldiol A p‐bromobenzoate (2), the absolute configuration at C(9) of (−)‐1 was assigned, and, together with extensive NMR experiments, the absolute configuration at C(10) and preferred conformations of (−)‐1 were determined. The absolute configuration of the hetero‐substituted cyclohexane ring was deduced in analogy from the X‐ray structure of 4, a derivative of the aldehyde 3, which was isolated from the same seaweed and is believed to be a degradation product of (−)‐1.
C45‐ and C50‐Carotenoids Part7 Total synthesis of (all‐E,2R,6R,2′R,6′R)‐ and (all‐E,2R,6S,2′R,6′S)‐2,2′‐Bis(4‐hydroxy‐3‐methylbut‐2‐enyl)‐γ,γ‐carotene (sarcinaxanthin)
Authors: Lanz Marc , Bartels Birgit , Pfander Hanspeter 
Published: December 2004

AbstractThe synthesis of sarcinaxanthin ((2R,6R,2′R,6′R)‐1), a symmetrical C50‐carotenoid with two γ‐end groups, isolated from Sarcina lutea and from Cellulomonas biazotea as major pigment, was based on the strategy C20 + C10 + C20 = C50 using camphoric acid as starting material for the C20‐end group 3. The key step of the synthesis is a ring enlargement of the cyclopentane derivative 10 with 2,4,4,6‐tetrabromocyclohexa‐2,5‐dien‐1‐one (TBCO) to give the cyclohexane derivative 11 (Scheme 1). The spectroscopic data of the synthetic compound are in full agreement with the data of the isolated product and give the final proof for the (2R,6R,2′R,6′R) chirality of natural sarcinaxanthin.
Synthesis of Carotenoids in the Gliding Bacteria Taxeobacter: (all‐E,2′R)‐3‐deoxy‐2′‐hydroxyflexixanthin
Authors: Bireher Christof , Pfander Hanspeter 
Published: December 2004

AbstractThe c40‐carotenoid (all‐E, 2′R)‐deoxy‐2′‐hydroxyflexixanthin (=1′,2′‐dihydroxy‐3′,4′‐didehydro‐1′,2′‐dihydro‐β,ψ‐caroten‐4‐one;(2′R)‐2) was synthesized according to a C15 + C10 + C10 = C40 strategy. The chiral centre was introduced into the C10‐end group by the enantioselective Sharpless dihydroxylation. The four building blocks were coupled by applying four consecutive Witting reactions. By comparison of the CD spectra of the synthetic (2′R)‐2 with those of 2 isolated from the gliding bacteria Taxeobacter, the configuration of natural 2 was determined as (2′R).
Biosynthesis of cis‐Jasmone: a pathway for the inactivation and the disposal of the plant stress hormone jasmonic acid to the gas phase?
Authors: Koch Thomas , Bandemer Katja , Boland Wilhelm 
Published: December 2004

AbstractFlowers of Jasminum rincospernum convert deuterium‐labeled jasmonic acid [2H5]‐4a and methyl 1,2‐didehy‐drojasmonate [2H4]‐8 into labeled cis‐jasmone [2H4]‐1. The labeling pattern of the resulting cis‐jasmone (1) is consistent with a Grob fragmentation of the didehydrojasmonic acid 8a by decarboxylation after protonation of the keto group. The pathway is also operative in leaves of several higher plants, including mono‐ and dicotyledonous specimens. In Lima beans besides cis‐jasmone (1) an equimolar mixture of trans‐ and cis‐isomers of methyl jasmonate (4) and epi‐4, is emitted after treatment with Jasmonic acid (4a). The relative ratio of 1 and 4/epi‐4 is critically dependent on the concentration of the administered jasmonic acid (4a) and the ambient temperature of the plant. Unlike 4a, the 1,2‐didehydrojasmonic acid (8a) is not able to induce volatile biosynthesis. Therefore, the transformation of 4a via 8 a into 1 appears to have a special importance for the irreversible inactivation and disposal of the plant stress hormone jasmonic acid to the gas phase and may serve, besides other modes of inactivation, as a shunt in case of high internal of the stress hormone 4a. The conversion of the biologically active jasmonic acid (4a) into the inactive and volatile cis‐jasmone (1) is the first example of a disposal of an inactive metabolite of a phytohormone to the gas phase as an infinite sink.
Investigation of the Chemo‐ and Stereoselectivity of the Ketene‐Claisen Rearrangement
Authors: Ernst Beat , Oehrlein Reinhold , Belluš Daniel , Gonda Jozef , Jeschke Rainer , Nubbemeyer Udo 
Published: December 2004

AbstractA novel type of ketene‐Claisen rearrangement in which the precursor of the rearrangement is generated in situ by reaction of optically active allyl thioethers with dichloroketene is described. A characteristic feature of this rearrangement is the excellent chemoselectivity in favor of allyl thioethers vs. allyl ethers, i.e., exclusive chirality transfer of the allylic sulfur moiety is observed with 12, 13, and 25‐‐27. The cyclic, optically active allyl thioethers (+)‐(R)‐4 and (−)‐(S)‐4 and the open‐chain allyl thioethers 11‐‐13 rearrange with in situ generated dichloroketene to the optically active thioesters (−)‐(S)‐28, (+)‐(R)‐28, and 31‐33, respectively. A chirality‐transfer of > 99% in the cyclic cases (+)‐(R)‐4 and (−)‐(S)‐4, and 96‐‐98 % in the open‐chain cases 11‐‐13 is observed. Furthermore, the dichloroketene‐Claisen rearrangement is characterized by a high asymmetric 1,2‐induction. The chiral allylic sulfides 25‐‐27 give the optically active thioesters 36‐‐38 with a 1,2‐induction > 99% as determined by NMR‐shift experiments.