bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Crystal Structure of Tricaesium Heptaphosphide–Ammonia(1/3) Cs3P7·3 NH3
Authors: Korber Nikolaus , Daniels Jörg 
Published: December 2004

AbstractRecrystallization of Cs3P7 from liquid NH3 yields the triammoniate Cs3P7·3 NH3, which loses the weakly bound NH3 of crystallization below 253 K. A low‐temperature crystal‐structure analysis shows that Cs3P7· NH3 consists of a framework of heptaphosphanortricyclane anions P and Cs+ cations with NH3 molecules completing the coordination of the cations. The framework is built from Cs3P7 layers connected by only few Cs…︁P interactions, the interlayer gap being filled by a two‐dimensional network of NH3. The Cs7P7 part of the structure completes a family of alkali‐metal‐polyphosphide substructures which range from [RbP7]2− or [CsP11]2− chains over [Cs2Pn]− layers (n = 7, 11) to now [Cs3P7] frameworks.
Synthesis and Structure of Functionalized Cyclododecadiynes and ‐dienes
Authors: Boss Christoph , Keese Reinhart 
Published: December 2004

AbstractThe cyclododecadiynes 3b–d, 8b–d, and 10b–c with functionalities in two propargylic positions, as well as the monofunctionalized diyne 13b have been prepared from simple open‐chain building blocks. In the DMPU ( = N,N'‐dimethylpropyleneurea)‐assisted ring‐closing alkylation of 1,7‐diynes, the twelve‐membered ring compounds have been prepared in yields of 16–55%. The preparation of the diene‐diyne 15 and the cyclododeca‐5,11‐diyne‐1,4‐dione 18 are described.
A Tricyclic Template Derived from (2S,4R)‐4‐Hydroxyproline for the Synthesis of Protein Loop Mimetics
Authors: Beeli Reto , Steger Mathias , Linden Anthony , Robinson John A. 
Published: December 2004

AbstractA tricyclic diketopiperazine, formally derived by coupling (2S,4S)‐4‐aminoproline (Pro(NH2)) and (2S,4R)‐4‐(carboxymethyl)proline (Pro(CH2COOH)), is synthesized starting from readily available (2S,4R)‐4‐hydroxyproline. The resulting tricyclic template has carboxy and amino groups to which a peptide chain may be attached. The Fmoc‐protected template 5 is incorporated into the cyclic molecule cyclo(‐Ala1‐Asn2‐Pro3‐Asn4‐Ala5‐) (6) where Pro(NH2)7 = Pro(CH2COOH)8 represents the template, using solid‐phase peptide synthesis with cyclization in solution. The molecule is shown by NMR and dynamic simulated annealing methods to adopt a preferred conformation in aqueous solution, which includes an extended backbone at the residues Asn2‐Pro3‐Asn4, and a type‐Iβ‐turn at . These studies show that this novel template may be used in the synthesis of cyclic peptide and protein mimetics having defined secondary structure in aqueous environments.
Naphthopyranquinone Antibiotics: Novel enantioselective syntheses of frenolicin B and some of its stereoisomers
Authors: Masquelin Thierry , Hengartnerb Urs , Streith Jacques 
Published: December 2004

AbstractTwo new enantioselective syntheses of the naphthopyranquinone antibiotic frenolicin B (1), of its enantiomer 2, and of its diastereoisomers 3 and 4 were accomplished using two different routes from optically active β‐Hydroxy esters (R)‐ and (S)‐11 and 18. β‐Hydroxy esters (R)‐ and (S)‐11 were prepared stereoselectively from optically active sulfenylacetates (S)‐ and (R)‐10, respectively (Scheme 2, Method A). Alternatively, compound 18 was obtained in excellent yield by enantioselective hydrogenation of the corresponding β‐keto ester 17, using a chiral ruthenium‐complex catalyst (Scheme 3, Method B). Subsequently, compounds (S)‐11 and 18 were transformed into frenolicin B (1). In analogy, Stereoisomers 2–4 were prepared from (S)‐ and (R)‐11 in good yields.
Synthesen neuer Phosphono‐Analoga von Pantethein‐derivaten
Authors: Neidlein R. , Li S. 
Published: December 2004

Syntheses of New Phosphono Analogues of Pantetheine DerivativesThe phosphono analogues 5 and 13 of pantothenate 4′‐(dibenzyl phosphate) and pantetheine 4′‐(dibenzyl phosphate), respectively, are prepared as intermediates for the synthesis of a coenzyme‐A phosphono analogue (Schemes 1 and 2). The synthesis of phosphono analogues 20 and 21 of oxapantetheine, which are structurally similar compounds to the phosphono analogue of pantetheine, is also described (Scheme 3).
Nucleotides. Part L. Aglycone protection by the (2‐dansylethoxy)carbonyl (= {2‐{[5‐(dimethylamino)naphthalen‐l‐yl]sulfonyl}ethoxy}carbonyl; dnseoc) group a new variation in oligodeoxyribonucleotide synthesis
Authors: Wagner Thomas , Pfleiderer Wolfgang 
Published: December 2004

AbstractThe (2‐dansylethoxy)carbonyl (= {2‐{[5‐(dimethylamino)naphthalen‐l‐yl]sulfonyl}ethoxy}carbonyl; dnseoc) group was employed for protection of the amino functions of the aglycone residues. The lactam function of 2′‐deoxyguanosine was on the one hand unprotected and on the other hand alkylated at O6 of the aglycone with the 2‐(4‐nitrophenyl)ethyl (npe) and 2‐(phenylsulfonyl)ethyl (pse) group, respectively. The syntheses of monomeric building blocks, both phosphoramidites and nucleoside‐ functionalized supports, are described for the three common 2′‐deoxynucleosides (2′‐deoxycytidine, 2′‐deoxyadenosine, 2′‐deoxyguanosine). As kinetic studies with the tritylated nucleosides showed, the dnseoc group is more labile towards DBU cleavage than the corresponding 2‐(4‐nitrophenyl)ethyl‐(npe) and [2‐(4‐nitrophenyl)ethoxy]carbonyl(npeoc)‐protected analogues (see Table 2). These results were confirmed by the very fast deprotection rate of the dnseoc groups at some oligonucleotides.
The Absolute Configuration of 3‐Methylpyrrolidine Alkaloids from Poison Glands of Ants Leptothoracini (Myrmicinae)
Authors: Koob Robert , Rudolph Christiane , Veith Hans Jiirgen 
Published: December 2004

AbstractThe absolute configuration of 3‐methylpyrrolidine alkaloids isolated from the poison gland of ants Leptothoracini was determined as (3R). The enantiomeric separation by chiral gas chromatography and unambiguous structural assignment of the target compounds are described.
An Unexpected Isomerization of N‐Aryl‐3‐amino‐4‐nitroisothiazol‐5(2H)‐imines to 2‐(Benzothiazol‐2‐yl)‐2‐nitroethene‐l, l‐diamines
Authors: Argilagos Dally Moya , Trimiño María I. García , Cabrera Arturo Macías , Linden Anthony , Heimgartner Heinz 
Published: December 2004

AbstractThe syntheses of several N‐aryl‐3‐amino‐4‐nitroisothiazol‐5(2H)‐imines 12 from 3, 3‐diamino‐2‐nitro‐thioacrylamides 11 are reported (Scheme 3). In polar solvents, a spontaneous isomerization of some of the prepared isothiazol‐5(2H)‐imines 12 yielded benzothiazoles 13 (Scheme 4). In the case of 2‐alkyl‐substituted derivatives of type 12, the isomerization occurred only at higher temperatures. Electronic influences of different substituents on the rate of the isomerization were studied, and a polar reaction mechanism is proposed in Scheme 6. The structures of 12e and 13e were established by X‐ray crystallography. Conformational analyses of 3‐(methylamino)‐2‐nitro‐N‐phenyl‐3‐(pyrrolidin‐1‐yl)thioacrylamide (111) by NMR and X‐ray methods were performed with the aim of explaining the distinct behavior of this amide towards Br2 or diethyl azodicarboxylate.
Isolation, Structure, and Biological Activities of Long‐Chain Catechols of Plectranthus sylvestris (Labiatae)
Authors: Juch Mathias , Rüedi Peter 
Published: December 2004

AbstractAntioxidant activity guided fractionation of extracts of the aerial parts of the title plant and HPLC separation yielded a series of oxygenated long‐chain alkylcatechols. Their structures were inferred by spectroscopic methods and chemical transformations to be the novel 4‐[(2S,4R,6S)‐4‐(acetyloxy)tetrahydro‐6‐pentyl‐2H‐pyran‐2‐yl]benzene‐1,2diol (1a), 4‐[(2S,4R6S)‐tetrahydro‐4‐hydroxy‐6‐pentyl‐2H‐pyran‐2‐yl]benzene‐1,2‐diol (1b), 4‐[(3S,5S)‐5‐(acetyloxy)‐3‐hydroxydecyl]benzene‐1,2‐diol (2a), 4‐[(3S,5S)3‐(acetyloxy)‐5‐hydroxydecyl]benzene‐1,2‐diol (2b), (3S,13Z)‐1‐(3,4‐dihydroxyphenyl)‐3‐hydroxydocos‐13‐en‐5‐one (3a), (Z)‐1‐(3,4‐dihydroxyphenyl)docos‐13‐en‐5‐one (4), besides the known l‐(3,4‐dihydroxyphenyl)icosan‐5‐one (5). The absolute configurations of the optically active compounds which are structurally related to the [n]‐gingerols (6) and ‐diols (7) were established by the high‐field 1H‐NMR application of Mosher's method. All compounds are in vitro potent antioxidants, inhibiting the Fe2+‐catalysed autoxidation of linoleic acid in the same order of magnitude as the commercial antioxidant 2,6‐di(tert‐butyl)‐4‐methylphenol (BHT). The dose‐dependent inhibitory effects on soybean‐lipoxygenase are in the μmol range, that of the most effective compound (3a) in the nmol range, hence being significantly more potent than the Known anti‐inflammatory and analgesic drugs indomethacin and nordihydroguaiaretic acid.
Variants of Solid‐State and Solution Structures of (η3‐Allyl)‐ {2‐[2′‐(diphenylphosphino)phenyl]‐4,5‐dihydrooxazole‐P,N}palladium(II) hexafluorophosphates and tetraphenylborates
Authors: Schaffner Silvia , Macko Ludwig , Neubufger Markus , Zehnder Margareta 
Published: December 2004

AbstractCrystal and solution structures of the enantiomerically pure and the racemic pairs of (η3‐allyl) {2‐[2′‐(diphenylphosphino)phenyl]‐4,5‐dihydro‐4‐phenyloxazole}palladium(II) hexafluorophosphates (1, and rac‐1, resp.) and tetraphenylborates (2, and rac‐2, resp.) as well as (η3‐allyl){2‐[2′‐(diphenylphosphino)phenyl]‐4,5‐dihydro‐4‐isopropyloxazole}palladium(II) tetraphenylborate (3) were characterized by X‐ray crystallography and 1H‐NMR spectroscopy. In the solid state, rac‐1 and rac‐2 proved to be disordered with both diastereoisomeric complexes in the crystal. The complexes 2 and 3 exist only in the ‘exo’ form. The X‐ray structures show that the [PdII(η3‐allyl)] moiety may adopt different configurations between a nearly symmetrical three‐electron PdII(π3‐allyl) system and an asymmetrical allyl group with a η1‐ and a η2‐bonding to the metal center. The [PdII(η3‐allyl)] system of rac‐1 and of ‘endo’ rac‐2 is closer to the former, and that of 2, ‘exo’‐rac‐2, and 3 closer to the later geometry. The 1H‐NMR spectra of the hexafluorophosphates 1 and rac‐1 show two sets of signals of the allylic protons in an ‘exo’/‘endo’ ratio of 2:3. The tetraphenylborates 2, rac‐2, and 3 give only one set of broad signals of the allylic protons.
Synthesis and Structure of a Macrocyclic Europium Complex and its possible role as a catalyst for phosphodiester transesterification
Authors: Haner Robert , Hall Jonathan , Rihs Grety 
Published: December 2004

AbstractThe synthesis and X‐ray crystal structure of a europium macrocyctic complex 1, an important catalyst used for the sequence‐specific cleavage of RNA, is reported. The role of this metal complex in facilitating phosphate transesterification is discussed.
Photochemistry of Tetraalkyl‐2H‐thietes
Authors: Mergenhagen Thomas , Margaretha Paul 
Published: December 2004

AbstractThe 3‐alkyl‐2,2‐dimethyl‐4‐(tert‐butyl)‐2H‐thietes 9a–c were obtained in several steps from the corresponding, newly synthesized, 3‐alkyl‐2‐(tert‐butyl)thiophenes 5a–c. Irradiation (254nm) of these tetraalkylated four membered S‐heterocycles leads to a photostationary equilibrium with enethiones 10a–c (thiete/enethione 3:1).
Some Unusual Products from the Thermal Reaction of Azulenes with Dimethyl Acetylenedicarboxylate
Authors: Magnussen Anette , Hansen Hans‐Jürgen 
Published: December 2004

AbstractThe thermal reaction of azulene‐1‐carbaldehydes 5 and 6 with excess dimethyl acetylenedicarboxylate (ADM) in decalin leads mainly to the formation of (1 + 1) and (1 + 2) adducts arising from the addition of ADM at the seven‐membered ring of the azulenes (cf. Schemes 2 and 4). The (1 + 2) adducts are formed in a homo‐Diels‐Alder reaction of ADM and isomeric tricyclic carbaldehydes which are derived from the primary tricyclic carbaldehydes by reversible [1s5s]‐C shifts (cf. Schemes 3 and 5). The thus formed pentacyclic carbaldehydes seem to undergo deep‐seated skeletal rearrangements (cf. Scheme 7) which result finally in the formation of the formyl‐tetrahydrocyclopenta[bc]acenaphthylene‐tetraesters 12 and 19, respectively. In other cases, e.g., azulene‐1‐carbaldehydes 7 and 8 (cf. Scheme 8), the thermal reaction with excess ADM furnishes only the already known tetracycfic (1 + 2) adducts of type anti‐26 to ‘anti’‐29. The thermal reaction of 1,3,4,8‐tetramethylazulene (9) with excess ADM in decalin resulted in the formation of two (1 + 2) and one (1 + 3) adduct in low yields (cf. Scheme 9). The latter turned out to be the 2,6‐bridged barrelene derivative 32. There are structural evidences that 32 is formed by similar pathways as the formyl‐tetrahydrocyclopenta[bc]acenaphthylene‐tetraesters (cf. Schemes 7 and 11). [2H3]Me‐Labelling experiments are in agreement with the proposed mechanisms (cf. Scheme 13).
Photoreduction of Triplet Benzophenone by Tertiary Amines: Amine molecular structure and ketyl radical yield
Authors: Raumer Markus Von , Suppan Paul , Haselbach Edwin 
Published: December 2004

AbstractThe photoreduction of triplet benzophenone by 14 tertiary amines was investigated. The ketyl radical yields do not correlate with the quenching rate constants, nor with the electron donor propensity of the amines. Individual structural features of the amines seem to determine the photoreduction yields.
Molecular Recognition of NADP(H) and ATP by Macrocyclic Polyamines Bearing Acridine Groups
Authors: Fenniri Hicham , Hosseini Mir Wais , Lehn Jean‐Marie 
Published: December 2004

AbstractThe macrocyclic polyamine‐based receptor BA bearing two acridine units makes use of combined electrostatic and stacking interactions for the binding of nucleotide polyphosphates and for the recognition of ATP and of NADPH (ka > 3 · 108 M), with a high selectivity for NADPH vs. NADP (ca. 103) and NAD(H) (> 106). The binding properties of this receptor towards a variety of substrates led to its in vitro application as a fluorescent probe for ATP. BA also interacts strongly with nucleic acids as shown by spectrophotometric, spectrofluorimetic, and electrophoretic mobility methods.
Selective N3‐ and 5′‐O‐Alkylation of 2′,3′‐O‐isopropylideneuridine with methyl iodide
Authors: Hovinen Jari 
Published: December 2004

AbstractThe 2′,3′‐O‐isopropylideneuridine (1) reacts with MeI in the presence of an excess of NaH in THF giving 2′,3′‐O‐isopropylidene‐5′‐O‐methyluridine (2). Prolonged reaction time gives rise to 2′,3′‐O‐isopropylidene‐3,5′‐O‐dimethyluridine (4). The use of an equimolar amount of base and alkylating agent results predominantly in methylation at N(3) (→ 3).
Metal Complexes with Macrocyclic Ligands. Part XLIV Kinetics of the Cu2+ incorporation into a macrocyclic ligand conjugated to proteins: Model studies for the d‘post‐labeling’ technique
Authors: Manzetti Matthias , Macko Ludwig , Neuburger‐Zehnder Margareta , Kaden Thomas A. 
Published: December 2004

AbstractThe kinetics of the Cu2+ complexation by macrocycles 1 (4‐[(l,4,8,11‐tetraazacyclotetradec‐1‐yl)methyl]‐benzoic acid) and 2 (N‐propyl‐4‐[(1,4,8,11‐tetraazacyclotetradec‐1‐yl)methyl]‐benzamide) as well as by macrocycle 1 conjugated to bovine serum albumin (bsa) and to ribonuclease A (rnase) were studied by stopped flow techniques. For 1 and 2, the kinetics were followed in the mM range monitoring the d‐d* absorption band of the Cu2+ complex. From the pH dependence of kobs, the rate law is v = [Cu2+] (kLH[LH] + k[LH2]), where kLH and k are the bimolecular rate constants for Cu2+ with the diprotonated (LH2) and monoprotonated (LH1) form of the ligand, respectively. The values are k = 1.7(1) M−1s−1 and kLH = 2.3(1) 105 M−1s−1 for 1, and k, = 0.28(9) M−1s−1 and kLH = 2.0(1) 105 M−1s−1 for 2. The kinetics of the Cu2+ incorporation into 1,2 and 1 conjugated to bsa and rnase, i.e., 3 and 4, respectively, were also followed using nitroso‐R salt as a metal indicator in the μM range, i.e., under conditions typical for the ‘post‐labeling’ technique to give radiolabeled monoclonal antibodies. In these cases, the reaction takes place between the 1:1 complex of Cu2+ with nitroso‐R‐salt and the macrocycle. At pH 6.5, the rates are very similar to each other indicating that the complexation properties of the macrocycle attached to a protein are not very different from those of the free ligand under comparable conditions.
Nucleotides. Part LII. Synthesis and biological activity of new base‐modified (2′–5′)oligoadenylate trimers
Authors: Kvasyuk Evgeny I. , Kulak Tamara I. , Tkachenko Olga V. , Sentyureva Svetlana L. , Mikhailopulo Igor A. , Suhadolnik Robert J. , Horvath Susan E. , Henderson Earl E. , Guan Ming‐Xu , Pfleiderer Wolfgang 
Published: December 2004

AbstractSome new (2′–5′)oligoadenylate trimers, i.e., 22–28, containing the antiviral nucleoside ribavirin (= 1‐(β‐D‐ribofuranosyl)‐1H‐1,2,4‐triazole‐3‐carboxamide; 7) and the synthetic cytokine 6‐(benzylamino)purine riboside (= N6‐benzyladenosine; 1) in different positions of the trimer, have been synthesized by the phosphotriester method. The selectively blocked nucleosides 2–6 and 8–11 and the 2′‐phosphodiesters 13 and 14, used for the oligonucleotide syntheses, were synthesized from the corresponding unprotected ribonucleosides 1 and 7, and isolated by silica‐gel column chromatography. The fully deblocked trimers 22–28 were purified by ion‐exchange chromatography on DEAE‐Senacell 23‐SS. The newly synthesized compounds were characterized by physical means. The ability of synthesized trimers to inhibit HIV‐1 replication and to improve RNase L activation were investigated. Some of the synthesized trimers showed also biological inhibition of HIV‐1 reverse transcriptase and HIV‐1‐induced syncytia formation. It was shown that AdoBn‐containing trimers inhibited HIV‐1‐induced syncytia formation > 1500‐fold, independently of the position of the AdoBn residue in the oligomer chain.
Glyconothio‐O‐lactones. Part III. Thermolysis of a 4,5‐Dihydro‐1,2,3‐ and a 2,5‐Dihydro‐1,3,4‐thiadiazole
Authors: Bernet Bruno , Mäder Thomas , Vasella Andrea 
Published: December 2004

AbstractAddition of CH2N2to 2,3:5,6‐di‐O‐isopropylidene‐1‐thio‐mannono‐1,4‐lactone (1) gave the 2,5‐dihydro‐1,3,4‐thiadiazole2and the 4,5‐dihydro‐1,2,3‐thiadiazole3. First‐order kinetics were observed for the thermolysis of3(Scheme 3) at 80–110° in C6D5Cl solution and of 2 (Scheme 3) at 20–35° in CDC13, respectively. The 1,2,3‐thiadiazole3led to mixtures of the thiirane9, the starting thionolactone1, the thiono‐1,5‐lactone8, and the enol ether7, while the isomeric 1,3,4‐thiadiazole2led to mixtures of the anomeric thiiranes9and12, the O‐hydrogenS,O,O‐ortholactone α‐D‐14, theS‐methyl thioester15, theS,S,O‐ortholactone13, and the 2,3:5,6‐di‐Oisopropylidene‐mannono‐1,4‐iactone (16). Pure products of the thermolysis were isolated by semipreparative supercritical fluid chromatography (SFC), whereas preparative HPLC led to partial or complete decomposition. Thus, the β‐D‐mannofuranosyl β‐D‐mannofuranoside10, contaminated by an unknown S species, was isolated by preparative HPLC of the crude product of thermolysis of3at 115–120° and partially transformed in CD3OD solution into the symmetric di(α‐D‐mannofuranosyl) tetrasulfide11. Its structure was evidenced by X‐ray analysis. Similarly, HPLC of the thermolysis product of2gave the enethiol17, the sulfide19, and the mercapto alcohol18as secondary products. Thermolysis of the thiirane9at 110–120° (Scheme 4) led to the anomeric thiirane12which was transformed into mixtures of the enethiol17and the enol ether7.Addition of H2O to17and7gave the corresponding hemiacetals18and20.The mechanism of the thermolysis of the dihydrothiadiazoles2and3, and the thiiranes9and12is discussed.
Rate Constants for the Addition of 2‐Hydroxy‐2‐propyl Radicals to Alkenes in Solution studied by laser flash photolysis
Authors: Martschke Rainer , Farley Robert D. , Fischer Hanns 
Published: December 2004

AbstractAbsolute rate constants for the addition of the highly nucleophilic 2‐hydroxy‐2‐propyl radical to eight fast‐reacting 1‐ and 1,1‐disubstituted alkenes in MeOH at room temperature have been determined by laser flash photolysis. Also the absorption spectra of the 2‐hydroxy‐2‐propyl and the benzylic and alkyl‐type adduct radicals are presented. The rate constants were obtained using various methods for the analysis of the kinetic traces and support earlier findings.
Changes in the Leaf Surface Chemistry of Apium graveolens (Apiaceae) stimulated by jasmonic acid and perceived by a specialist insect
Authors: Stanjek Volker , Herhaus Christian , Ritgen Ulf , Boland Wilhelm , Städler Erich 
Published: December 2004

AbstractTreatment of celery leaves (Apium graveolens, cv. secalinum) with Jasmonic acid (JA, 1) or analogues of amino‐acid conjugates of Jasmonic acid such as the leucine conjugate with 1‐oxoindan‐4‐carboxylic acid (IN‐ILE, 2) stimulated the biosynthesis of the furanocoumarins psoralen (6), xanthotoxin (8), bergapten (7), and isopimpinellin (9). Besides the increase of the compounds within the leaf, a significant amount (ca. 20%) of the total furanocoumarins was deposited on the surface of the leaf. The two monomethoxy furanocoumarins, 7 and 8, began to increase steadily and simultaneously within the leaf and on the leaf surface ca. 40 h after the onset of the jasmonic‐acid stimulus. Within the leaf, the ratio 7/8 was ca. 1.3:1.0, while among the surface lipids 8 dominated (7/8 0.8:1.0), indicating that the export of the compounds to the surface is not a simple diffusive translocation along the oil‐ducts. Females of the carrot fly (Diptera, Psilidae) responded with an increased oviposition to the altered leaf surface chemistry of the JA‐treated celery plants. The effect shown for total leaves was corroborated by surrogate leaves treated with leaf‐surface extracts of JA‐induced leaves. Based on the known stimulation of oviposition by furanocoumarins, we conclude that the enhanced amount of furanocoumarins on the surface can explain the insects' preference for the JA‐stimulated plants. This is the first report of a JA‐induced change of the surface chemistry of a plant and an increase of the acceptability of treated leaves for a specialist insect, like the carrot fly.
Stereoselective Ring Opening of Electronically Excited Cyclohexa‐2, 4‐dienones: Cause and effect
Authors: Quinkert Gerhard , Scherer Stefan , Reichert Dietmar , Nestler Hans‐Peter , Wennemers Helma , Ebel Andreas , Urbahns Klaus , Wagner Klaus , Michaelis Klaus‐Peter , Wiech Gerhard , Prescher Günter , Bronstert Bernd , Freitag Bernd‐Jürgen , Wicke Ilka , Lisch Dietmar , Belik Pavel , Crecelius Thorsten , Hörstermann Dirk , Zimmermann Gottfried , Bats Jan W. , Dürner Gerd , Rehm Dieter 
Published: December 2004

AbstractThe two conformers of a cyclohexa‐2, 4‐dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene‐ketenes (and descendents thereof)‐ Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring CO group. In these cases, only one of the two anticipated diene‐ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa‐2, 4‐dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene‐ketenes into a variety of compound classes. Novel compound classes accessible to diene‐ketenes are seven‐membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene‐(N, O)‐ketene acetals) and β‐lactams (by Staudinger reaction).