bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cob(I)alamin Differentiating Alkenes During Saturation
Authors: Schönholzer Peter , Süss Daniel , Wan Terence S. , Fischli Albert 
Published: December 2004

AbstractThe olefins 2, 7, 11, and 19, have been reduced using catalytic amounts of cob(I)alamin(I(I)). During a slow saturation, the catalyst is able to differentiate the two diastereotopic faces of the endocyclic double bonds in 11 (t1/2 4 h,. cf. Scheme 3) are reduced much faster. A rationalization of the data can be obtained formulating tertiary alkylcobalamins as intermediates. Of the oxime 6 (cf. Scheme 2) and the p‐ bromobenzoate 23 (cf. Scheme 5) the structures have been determined by X‐ray analysis.
Absolute Configuration of Gilmaniellin
Authors: Snatzke GÜNther , Tamm Christoph 
Published: December 2004

AbstractThe absolute configuration of dechlorogilmaniellin (2) could be determined from its chiroptical data by applying coupled‐oscillator theory to the CD couplet around 272 nm and from the sign of its n →π* Cotton effect. Gilmaniellin (1) has the same absolute configuration.
Oxygenation of Dimethylsulfoxide and Copper‐Catalyzed Autoxidation of Substituted Benzoins
Authors: Gampp Harald , Haspra Doris , Spieler Walter , Zuberbühler Andress D. 
Published: December 2004

AbstractThe catalytic activity of autoxidized copper (I) in the oxidation of para‐disubstituted benzoins in dimethylsulfoxide by O2 was studied both kinetically and by product analysis. Stoichiometry (1), accounts for more than 80% of the reaction. The catlytic oxydation was followed by monitering th consumption of O2 manometrically by a fully automatic apparatus.
equation image
(X = H, CH3, OCH3, C6H5 CI)A redox shuttle mechanism is proposed, where the rate‐determining step is the autoxidation of Cu(I) followed by a rapid oxidation of the substrate by an oxocupric species. The redox stiochiometry (I) corresponds to that found for external monooxy‐genases (or mixed‐function oxidases), and the significance of our results with respect to analogous catalytic systems is discussed.
Ein neuer Zugang zu Bicyclo[4.1.0]heptan‐Derivaten
Authors: Spreitzer Helmut , Buchbauer Gerhard 
Published: December 2004

A New Approach to Bicyclo[4.1.0]heptane DerivativesThe reaction of the dienone 1 with ethyl α‐bromoacetate does not furnish the expected glycidic acid ester 2 but leads to the bicyclo[4.1.0]heptenone derivative 3. The structure of this new compound has been proved by means of spectroscopic methods (1R, 1H‐NMR, 13C‐NMR, MS). The elucidation of the configuration at C(7) could be realized by measuring a NOE effect. Other α‐alkylated α‐bromoacetates react with 1 in the same manner.
8α,9α‐Epoxy‐7‐oxoroyleanon, ein Diterpen‐Epoxychinon aus einer abessinischen Plectranthus‐Art (Labiatae)
Authors: Rüedi Peter 
Published: December 2004

8α,9α‐Epoxy‐7‐oxoroleyanone, a Diterpenoid Epoxyquinone from an Abyssinian Plectranthus Species (Labiatae)Reexamination of the title plant, in additon to the previously identified abietanoid hydroxy‐1,4‐benzoquinones 1a, 1b, 1c, 1e, 1f, 1g, and 1h, yielded the known 7α‐acetoxyroleanone ( = 7‐O‐acetylhorminone; 1d) and the novel 8α, 9α‐epoxy‐7‐oxoroyleanone (2a). Spectroscopic methods, partial synthesis by epoxidation of 7‐oxoroyleanone (1h), and chiroptical correlation establish the structure 2a. Royleanone 2a is the first diterpenoid epoxyquinone isolated so far. Moreover, a detailed 13C‐NMR analysis of the royleanones 1b, 1c, 1e, 1g, and 1h lead to the complete assignment of their spectra.
3‐Lithiopyrroles by Halogen‐Metal Interchange of 3‐Bromo‐1‐(triissopropylsilyl)pyrroles. Synthesis of Verucarin E and Other 3‐Substituted Pyrroles. Preliminary Communication
Authors: Muchowski Joseph M. , Naef Reto 
Published: December 2004

Abstract3‐Lithio‐1‐(trimethylsilyl)pyrrole (7, Schem 2), obtained by halogen‐metal interchange from the 3‐bromo compound 2, reacted with various electrophilic reagents to provide products, which on fluoride ion desilylation, gave 3‐substituted pyrroles in good overall yields. One such pyrrole 13 (Schem 3), was converted into 2‐formyl‐3‐octadeclpyrrole (14), reputed to be a metabolite of the marine sponge Oscarella lobularis.3,4‐Dibromo‐1‐(triisopropylsityl)pyrrole (5) was efficiently transformed, by a process involving two consecutive bromine‐lithium exchange reactions (Scheme 4), into the antibiotic verrucarin E 17.
New Carbonyl Compounds in the High‐Boiling Fraction of Lavender Oil. 3rd Communication
Authors: Kaiser Roman , Lamparsky Dietmar 
Published: December 2004

AbstractThe occurrence of a series of new constituents which can be considered as Diels‐Alder adducts of methyl vinyl ketone and ocimene (→1–4), myrcene (→9, 10) or β‐far‐nesene ( →11, 12), respectively, was reported. Furthermore, the structures of four isomeric cyclohexene derivatives could be established as adducts 21–24 of (E, Z)‐ and (E, E)‐1,3,5‐undecatrience and methyl vinyl ketone. Another series of constituents having the norbornane skeleton represents adducts 25–32, and 33–40 of methyl cyclopentadiene and 1‐octen‐3‐one or methyl vinyl ketone, respectively. In accordance with Alder's endo‐rule the endo‐isomers are preponderant in the natural as well as in the synthetic mixtures. Most of these constituents could also be identified in a lavender absolute as well as in a freshly prepared hexane extract of lavender flowers (Lavandula officinalis CHAIX).
Stoffwechselprodukte von Mikroorganismen 227. Mitteilung. Isolierung und Strukturaufklärung von Rutamycin B
Authors: Wuthier Damian , Keller‐Schierlein Walter , Wahl Barbara 
Published: December 2004

Isolation and Structure of Rutamycin BBotrycidin was found to be identical with rutamycin. From the cultures of the actinomycete producing botrycidin and the venturicidines. A and B, a fourth antifungal antibiotic, rutamycin B, was isolated. Through a series of degradation products its structure could be correlated to that of rutamycin, which had been determined before by an X‐ray structural analysis. Rutamycin B has been identified as 12‐deocy‐rutamycin.
Model Compounds for Rhodospin and Bacteriorhodopsin: Synthesis, and 1H‐ and 13C‐NMR Study
Authors: Rabiller Claude , Danho Doubou 
Published: December 2004

AbstractThe reaction of all‐trans‐retinal and 5‐(2,6,6‐trimethylcyclohexeyl)‐3‐methyl‐2,4‐pentadienal with amino acids, amino esters and their salts was studied. The structure of the polyenic imines and iminium salts thus prepared was elucidated with the aid of 1H‐and 13C‐NMR spectroscopy. The condensation results in an equilibrium between the imine and its zwitterionic form as shown by variable‐temperature 13C‐NM measurements. Addition of an inorganic salt (LiClO4) favours the zwitterionic form. Comparison of the 13C chemical shifts of these species with those obtained from the protonation of the corresponding imino‐ester gave the percentage of the two forms. The species prepared from the amino acids constitute model compounds, and rhodopsin and bacteriorhodopsin are believed to exhibit similar behaviour.
Eine thermische, intramolekulare [2 + 2]‐Cycloaddition eines Allenyl‐benzols; Synthese von Allenylbenzolen durch säurekatalysierte Dienol‐Benzol‐Umlagerung
Authors: Summematter Walter , Heimgartner Heinz 
Published: December 2004

A thermal Intermolecular [2 + 2]‐Cycloaddition of an Allenyl‐Allyl‐Benzene; Synthesis of Allenylbenzenes via Acid‐Catalyzed Dienol‐Benzene RearrangementA few years ago, it has been shown that the acid‐catalyzed dienol‐benzene rearrangement of 2‐propinyl‐substituted cyclohexadienols is a convenient synthesis for allenyl‐substituted benzene derivatives. The cyclohexadienols 20 and 21 were prepared via C‐alkylation of the corresponding phenols with 2‐propinylbromide (Scheme 3), followed by reduction of the cyclohexadienone 13 and 17 with LiAlH4. Treatment of 20 and 21 with p‐toluenesulfonic acid in ether at −15°) yielded the desired allenyl benzenes 8 and 9, respectively, via [3,4]‐sigmatropic rearrangements (Scheme 4). The 2‐propinylbenzenes 22–24, formed via [1,2]‐sigmatropic shift of the 2‐propinylgroup, were found as by‐products. Thermolysis of allenyl benzene 8 in decane yielded two bicyclic (25 and 26) and two tricyclic products (27 and 28; Scheme 5). For the formation of 25 and 26, a pericyclic reaction mechanism (Scheme 6) as well as a mechanism via biradical intermediates (Scheme 7) is discussed. A [2 + 2]‐cycloaddition of the α,β‐allenic and the allylic C,C‐double bound of 8 led to the tricyclic products 27 and 28 (Scheme 9). All attempts to realize a [1,7]‐sigmatropic H‐shift in the allene 9 failed so far, and the starting material underwent a rapid polymerisation.
Improved Synthesis of Oligodeoxyribonucleotides by Solid‐Phase Phosphotriester Method Utilizing O6‐[2‐(p‐Nitrophenyl)ethyl]‐2′‐deoxyguanosine Derivatives
Authors: Chollet André , Ayala Edgar , Kawashima Eric H. 
Published: December 2004

AbstractThe synthesis of oligodeoxyribonucleotides on a cross‐linked polystyrene solid support utilizing stable mono‐ and dinucleotide phosphotriester building blocks is presented. The use of O6[2‐(p‐nitrophenyl)ethyl]‐2′‐deoxyguanosine derivatives yields cleaner DNA fragments by suppressing side reactions. Modifications improving the phosphotriester methodology are presented. The purification methods and analysis of synthetic oligodeoxyribonucleotides are described.
Water‐Exchange Mechanism of Tetraaquapalladium(II). A Variable‐Pressure and Variable‐Temperature Oxygen‐17 NMR Study
Authors: Helm Lothar , Elding Lars I. , Merbach André E. 
Published: December 2004

AbstractWater exchange of square‐planar Pd(H2O)24+ has been studied as a function of temperature (240 to 345 K) and pressure (0.1 to 260 MPa, at 324 K) by measuring the 17/O‐FT‐NMR line‐widths of the resonance from coordinated water at 27.11 and 48.78 MHz. The following exchange parameters were obtained: k298ex = (560 ± 40) s−1, ΔH* = (49.5 ± 1.9) kJ mol−1, ΔS* = – (26 ± 6) J K−1 mol−1 and ΔV* = – (2.2 ± 0.2) cm3 mol−1. The values refere to an aqueous perchlorate medium with an ionic strength between 2.0 and 2.6 m and a perchloric‐acid concentration between 0.8 and 1.7 m, and are interpreted in terms of an associative (a) activation for the exchange. The exchange rate for Pd(H2O)24+ is 1.4 × 106 times faster than for Pt(H2O)24+ at 298 K. A comparison with reactions between other nucleophiles and Pd(H2O)24+ is also made.
Etudes sur les composés organométalliques partie XX Sélectivité de l'addition 1,4 de composés benzyliques du titane IV avec la benzylidéneacétone
Authors: Roulet Daniel , Capéros José , Jacot‐Guillarmod André 
Published: December 2004

AbstractStudies of Organometallic Compounds, XX. Selectivity of 1,4‐Addition of Benzyltitanium Compounds with BenzylildenacetoneTetrabenzyltitanium and dialkoxydibenzyltitanium compounds give essentially 1,4‐ addition with trans‐4‐phenyl‐3‐buten‐2‐one.
Drüsenfarbstoffe aus tropischen Labiaten: Parviflorone aus Plectranthus strigosus BENTH.
Authors: Alder Aldredo Carlos , Rüdi Peter , Eugster Conrad Hans 
Published: December 2004

AbstractRed‐Coloured Abietanoids from Leaf‐Glands of Plectranthus strigosus BENTH.Chromatographic examination of the red‐coloured diterpenoids from the South‐African title plant yielded the following compounds: parviflorone A(1), parviflorone B (2), parviflorone C(3), parviflorone E (4) parviflorone D (5), parviflorone F (6), parviflorone G (7), and parviflorone H (8). Compounds 7 and 8 represent new variants of these quinone methides.
Synthese von neuen Morphin‐Teilstrukturen des Typs 15,16‐Secomorphinan
Authors: Révész László 
Published: December 2004

AbstractSynthesis of New Morphine Partial Structure 15,16‐SecomorphinanThe synthesis of a new morphine partial structure, 15,16‐secomorphinan, is described. One of the series, (±)‐15, 16‐secocyclorphan (5), has the analgesic potency of morphine and exhibits good binding to the opiate receptor.
Monoolefin and Diene Cycloaddition Induced by Transition‐Metal Carbonyls. Cyclodimerization of 5,6‐Dimethylidene‐7‐oxabicyclo[2.21]hept‐2‐ene Catalyzed by Dodecacarbonyltriosmium
Authors: Vioget Philippe , Bonivento Massimiliano , Roulet Raymond , Vogel Pirre 
Published: December 2004

AbstractThe products generated by heating 5,6‐dimethylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene (1) with Fe2(CO)9, Ru3(CO)12, Os3(CO)12, Cr(CO)3(MeCN)3, (or W(CO)5(MeCN) or by treatment with Fe‐atoms have been characterized by spectroscopic methods. Apart from the expected η2‐ and η4‐complexes of the triene 1, condensation products are formed which arise from the formal [4 + 2]‐cyclodimerization of 1 involving the endocyclic double bond of one molecule and the diene moiety of a second. The [4 + 2]‐cyclodimerization is catalyzed by Os3(CO)12 in MeOH and gives 1,4‐epoxy‐7‐methoxy‐2,3‐dimethylidene‐1,2,3,4,4a,9,9a,10‐octahydroanthracene (15)). Fe‐Atoms induce a stereoselective [2 + 2]‐cyclodimerization pf 1 which involves its endocyclic double bond and produces the dimer 8.
Photochemical reactions. 139th Communication. Photochemistry of acylsilanes: 1. Siloxcarbene formation versus γ‐H‐abstraction
Authors: Scheller Markus E. , Frei Bruno 
Published: December 2004

AbstractThe Syntheses and the photolyses of the acylsilane 1 and the corresponding methyl ketone 2 are described. On n,π*‐excitation, the silyl ketone 1 as well as the methyl ketone 2 undergo a Norrish type II reaction involving γ‐H‐abstraction and fragmentation to the diene 12, and acetone (20) or the acylsilane 26, respectively. The methyl ketone 2, but not the acylsilane 1, isomerizes to cyclobutanols (21A‐D). Additionally, compound 1 shows photochemical behavior typical of acylsilanes undergoing rearrangement to the siloxycarbene intermediate c. Insertion of c into the OH‐ond of the enol 28 leads to compound 13. Initial trapping of the siloxycarbene c by H2O, however, gives rise to the formation of compounds 16–18. As minor photolysis products of 1, compounds 14 and (Z)‐15 were formed; however, on vapor phase thermolysis (520°) of 1, compounds 14 and (E/Z)‐15 were obtained in 92% combined yield. To a small extent the acylsilane 1 also undergoes Norrish type I cleavage leading to the acid 19.
(all‐E)‐1,3,5,7‐Octatetraene: Electron‐Energy‐Loss and Electron‐Transmission Spectra
Authors: Allan Michael , Neuhaus Louis , Haselbach Edwin 
Published: December 2004

AbstractElectron‐energy‐loss and electron‐transmission spectra of (all‐E)‐1,3,5,7‐octatetraene were recorded with a trochoidal electron spectrometer. The energy‐loss spectra reveal two triplet states at 1.73 and 3.25 eV (0,0‐transitions), the UV‐active 11Bu state at 4.40 eV, and a higher‐lying singlet state at 6.04 eV. The 21Ag state recently reported to be the lowest excited singlet state in this polyene, could not be observed. This failure is probably de to a small excitation cross section under the scattering conditions used and the presence of the second triplet sate in the pertinent energy region. The electron‐transmission spectrum revealed three resonances (i.e. short‐lived anion states) at 1.5, 2.5, and 4.15 eV.
Bonding Capabilities of the Biochemical Buffer TRIS toward Copper(II) Ion. Structure and Magnetic Properties of Binuclear and Tetranuclear Systems
Authors: Masi Dante , Mealli Carloo , Sabat Michal , Sabatini Antonio , Vacca Alberto , Zanobini Fabrizio 
Published: December 2004

AbstractFollowing X‐ray crystal structure studies, the products of the reaction between Cu(II) halides and tris(hydroxymethyl)methylamine (TRIS) can be formulated as [Cu(TRISH−1)(TRIS)]2X2 and [Cu(TRISH−1)X]4 (X  Cl, Br). TRISH−1 is the deprotonated ligand. Initial metal‐ligand stoichiometric ratios of 1:2 and 1:1 are required to obtain the former and the latter species, respectively. Relevant crystal data for the dimeric compound with X  Br are: monoclinic, a = 11.39(2), b = 10.049(2), c = 12.149(2) Å, β = 95.83(2)°, space group P21/c, Z = 2. The tetramer with X  Cl crystallizes in teh triclinic space group P 1 with a 9.182(1), b = 9.120(2), c = 8.817(1) Å, α = 88.95(1), β = 87.01(1), γ = 84.13(1), Z = 1. In the dimer, two square planar Cu(II)‐units are held together by two H‐bonds of the type OH …︁ O, which involve the O‐atoms coordinated to the metals. The formation of an eight‐membered cycle containing two metal ons ensues. The tetramer contains two dinuclear units formed by two metal centers, square planar in first approximation, which share one edge; the arrangement is significantly puckered at this vector. One of these bridging O‐atoms has μ3 character as it serves as a weak apical donor for a Cu‐atom of another binuclear unit. Thus a step‐like geometry of the central core is obtained. Both compounds have constant magnetic moments at least down to the liquid N2 temperature. In this respect, they differ from other complexes of Cu(II) having comparable geometries, but temperature‐dependent magnetic moments.
Synthese von optisch aktiven Carotinoiden mit 3,5,6‐Trihydroxy‐5‐6‐dihydro‐β‐Endgruppen
Authors: Buchecker Richard , Marti Urs , Eugster Conrad Hans 
Published: December 2004

AbstractSyntheses of Optically Active Carotenoids with 3,5,6‐Trihydroxy‐5,6‐dihydro β‐End GroupsFor the specification of the relative and absolute configuration in carotenoids with 3,5,6‐trihydroxy‐5‐6‐dihydro β‐end groups, several ionone derivatives and carotenoids bearing this end group were synthesized. Acid‐catalyzed hydrolysis of (3S,5S,6R)– acetoxy‐5,6‐epoxy‐5,6‐dihydro‐β‐ionone (7) and of its (3S,5R,6S)‐isomer (13) gave the diols 8 and 15, respectively, with exclusive inversion at c(5) (Scheme 2). Compared to this, mild acid hydrolysis of caroten‐5‐6‐expoxides in the presence of H2O resulted in the formation of 5,6‐diols with either inversion or retention of the configuration at C(6) (Scheme 3). Spectroscopic data allowed us to distinguish the relative configurations (3R*,5S*,6S*) (see A), (3R*,5R*,6R*) (see B), (3R*,5S*,6R*) (see C), and (3R*,5R*,6S*) (see D), of the 3,5,6‐trihydroxy‐5‐6‐dihydro β‐end groups. Syntheses of the optically active carotene‐hexols 20 and 21 and comparison with published data led to a revision of the structure of mectrazanthin (now formulated as 20), heteroxanthin (now formulated as 28), and further carotenoids with 3,5,6‐trihydroxy end groups.
Structure Revision of the Rauwolfia Alkaloid Raucaffricine
Authors: Schübel Helmut , Treiber Arno , Stökigt Joachim 
Published: December 2004

AbstractThe previous structure of the Rauwolfia alkaloid raucaffricine (vomilenine‐α‐D‐galactoside) has been revised to be vomilenine‐β‐D‐Glucoside by enzymatic and NMR studies.
Comment on the Estimation of the Dimerisation Constant of Caffeine
Authors: Stamm Helmut , Timeus Friedrich 
Published: December 2004

AbstractReasons for the low reliability of the Compare e.g. former results cited in [3][4] with our results in [3].
H‐NMR estimation of the dimerisation constant of caffeine in D2O are discussed. The main reasons are (1) strong influence of small variations in the monomer shifts δ0 which are to be determined by extrapolation, and (2) disturbance by the formation of higher oligomers. The dilemma ist that attempts to minimize errors from (1) increase the influence of (2) and vice versa.
Conformational Equilibria in trans‐1,2‐Diarylethylenes Manifested in their Emission in Solution. Part VI. Heterocyclic Analogues, their Triplets and Exciplexes
Authors: Wismontski‐Knittel T. , Das P. K. , Fischer E. 
Published: December 2004

AbstractSolutions of heterocyclic analogues of 2‐styrylnaphthalene (2‐St‐N), with benzo[b]thiophene and benzo[b]furan groups replacing the 2‐naphthyl group, exhibit emission anomalies similar to those reported for 2‐St‐N, the most prominent one being a variation of the emission spectra with the excitation wavelength. The exciplexes formed when emission is quenched by N,N‐dimethylaniline (DMA) show a smaller variation of their emission maxima. Ground‐state rotamers may be responsible for the anomalies. The lifetimes of regular fluorescence in toluene are ≤ 2 ns, and our equipment did not allow to determine whether or not the decay is mono‐exponential. Exciplex lifetimes in toluene are 20‐30 ns. The triplets (λ  500‐520 nm) are characterized by short lifetimes (180‐190 ns) and appear to have substantial contributions from twisted configurations.
Bond Angles in Lactones and Lactams
Authors: Nørskov‐Lauritsen Leif , Bürgi Hans‐Beat , Hofmann Peter , Schmidt Helmut R. 
Published: December 2004

AbstractThe carbonyl group in lactones and, to a lesser extent, in lactams tends to show a CCO angle that is larger than the OCO or NCO angle, the difference increasing in magnitude as the ring size decreases. The observed trend provides information on ratios of force constants characterising the flexibility of the s‐cis‐ester group and may be interpreted in terms of incipient chemical reaction to −O(CH2)nCO+. Molecular orbital calculations (MINDO/3, MNDO, EH) for model compounds provide an electronic interpretation of this angle difference in terms of an anomeric interaction between the p‐type lone pair on the carbonyl O‐atom and the antibonding C‐O or C‐N orbital.
Stereoselective Double Functionalization of Iron‐Carbonyl Complexes of 5,6,7,8‐Tetramethylidenebicyclo[2.2.2]oct‐2‐ene. Crystal Structure and Absolute Configuration of (–)‐trans‐μ‐[(2S,5R,7S)‐C,5,6,C‐η:C,7,8,C‐η‐(6,7,8‐trimethylidene‐5‐((Z)‐2‐oxopropylidene)‐2‐bicyclo[2.2.2]octyl acetate)]‐bis(tricarbonyliron)
Authors: Tagliaferri Enrico , Campiche Philippe , Roulet Raymond , Gabioud Raphy , Vogel Pierre , Chapuis Gervais 
Published: December 2004

AbstractThe Friedel‐Crafts monoacylation of trans‐η‐[(1RS,2RS,4SR,5SR,6RS,7SR,8SR)‐C,5,6,C‐η:C,7,8,C‐η‐(5,6,7,8‐tetramethylidene‐2‐bicyclo[2.2.2]octyl acetate)]‐bis(tricarbonyliron) ((±)‐5) is highly stereoselective and yields trans‐η‐[(1RS,2RS,4RS,5SR,6RS,7RS,8SR)‐C,6‐η,oxo‐σ:C,7,8,C‐η‐(6,7,8‐trimethylidene‐5‐((Z)‐2‐oxopropylidene)‐2‐bicyclo[2.2.2]octyl acetate)]‐bis(tricarbonyliron) ((±)‐8) which equilibrates with the trans‐η‐[(1RS,2RS,4RS,5SR,6RS,7RS,8SR)‐C,5,6,C‐η:C,7,8,C‐η‐(6,7,8‐trimethylidene‐5‐((Z)‐2‐oxopropylidene)‐2‐bicyclo[2.2.2]octyl acetate)]‐bis(tricarbonyliron) ((±)‐9) on heating. Optically pure (–)‐9 has been prepared from the corresponding optically pure alcohol (+)‐4. The structure and absolute configuration of (–)‐9 was established by single‐crystal X‐ray diffraction.