bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selektive Synthesen mit Organometallen I. Konfigurativ einheitliche Folgeprodukte aus Alkenylkalium‐Zwischenstufen
Authors: Schlosser Manfred , Hartmann Jürgen , David Victor 
Published: December 2004

AbstractMethyl groups in positions adjacent to an olefinic double bond can be metalated without cis/trans isomerisation. On the other hand configurational changes can be brought about via metalotropy; under equilibrium conditions the Z isomers (metal cis to an alkyl in β position) predominate overwhelmingly. This behaviour opens new stereoselective routes of high preparative utility.
Reaktionen von Glutaminsäuredimethylester im Massenspektrometer. 21. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen
Authors: Lerch Elsbeth , Hesse Manfred 
Published: December 2004

AbstractThe mass spectral fragmentation of dimethyl glutamate (1) and its deuterated derivatives 1a, 1b and 1c has been investigated. By loss of a methoxycarbonyl group from the molecular ion an ion of m/e 116 is generated. The latter splits off methanol (m*), the resulting fragment of m/e 84 giving raise to the base peak of the spectrum. Only part of the hydrogen transferred to the leaving group originates from thc amino group, as was suggested earlier [2] [3]. Basing on experiments with deuterated compounds we propose an additional mechanism for the reaction, i.e. hydrogen transfer from C(3) to methoxyl. The fragment generated by both processes is most likely to be a pyrrolinonium ion. Thermal side reactions in the mass spectrometer (formation of pyroglutamic acid ester) followed by fragmentation may lead to the same ion. – The mechanisms discussed are supported by the mass spectral fragmentation of N‐acetyl‐glutamic acid diesters 3, 3a, 3b and 3d and of the N, N‐dimethyl derivatives 4 and 4a. – The fragmentation reactions investigated are similar to some of 1,3‐trimethylenediamine derivatives [7]. This means that there are parallels in the mass spectral fragmentation of difunctional compounds irrespective of the nature of the functional groups.
Cycloadditionen von Heterocumulenen an CN‐Bindungssysteme. 3. Mitteilung. Bildung von Dihydro‐1,3,5‐oxadiazin‐ und Perhydro‐s‐triazinthionen bei der Reaktion von Iminodithiocarbonaten und Azomethinen mit Aroylisothiocyanaten
Authors: Milzner Karlheinz , Seckinger Karl 
Published: December 2004

AbstractThe iminodithiocarbonates 5a–5g and the N‐(p‐methoxybenzylidene)amines 6a–61 undergo 4 + 2‐cycloaddition with the aroyl isothiocyanates 4a–4f to yield the expected dihydro‐1,3,5‐oxadiazine‐4‐thiones 7, 8 and 14.The addition of the aroyl isothiocyanates 4a–4f to the azomethines 11a–11c and 15a–15f, however, furnishes both the 4 + 2‐cycloaddition products 12 and 16 and the perhydro‐s‐triazine‐2‐thiones 13a–13j. The mechanism of formation is discussed.
Grignard‐Addition an Pyridin‐N‐oxid
Authors: Schiess Peter , Monnier Charles , Ringele Peter , Sendi Ebrahim 
Published: December 2004

AbstractAddition of phenyl‐, alkyl‐, alkenyl‐ and alkinyl‐Grignard reagents to pyridine‐N‐oxide in THF leads to 5‐substituted (2Z, 4E)‐pentadien‐aldoximes 6 having (E) (syn)‐configuration of the C, N‐double bond. The unsaturated oximes are shown to arise through an electrocyclic ring opening reaction from the primary Grignard adducts 5. These can be trapped by protonation at low temperature.
Isolierung, Konstitution und Synthese der (R)‐(−)‐Eucominsäure
Authors: Heller Werner , Tamm Christoph 
Published: December 2004

AbstractFrom the bulbs of Eucomis punctata L'Hérit. (Liliaceae) and of a hitherto undefined species of Eucomis a new optically active phenolic carboxylic acid, eucomic acid, was isolated. Structure 1 was assigned on the basis of chemical and spectral evidence. The absolute configuration of eucomic acid was determined by its correlation with piscidic acid ((2 R, 3 S)‐2‐(4′‐hydroxybenzyl)‐tartaric acid) (8). Consequently, eucomic acid is (R)‐(−)‐2‐(4′‐hydroxybenzyl)‐malic acid (1). For the stereospecific synthesis, methyl cis‐p‐methoxybenzylidene‐succinic acid (22) was transformed into the γ‐lactone 24 which, by catalytic hydrogenolysis, yielded (±)‐2‐(4′‐hydroxybenzyl)‐malic acid 1‐methyl ester (27). Resolution with (−)‐quinine led to the enantiomeric acids 29 and 30. The methyl ester of the levorotatory enantiomer 30 was identical with the dimethyl ester 3 of 4′‐O‐methyl‐eucomic acid.
Biosynthese der Cytochalasane. Teil II Die Grundbausteine von Cytochalasin D
Authors: Lebet Claude‐René , Tamm Christoph 
Published: December 2004

AbstractA number of potential 14C‐ and 3H‐labelled precursors were fed to growing cultures of Zygosporium masonii after the rate of formation of cytochalasin D had been measured. By chemical degradation of [14C]‐ and [3H, 14C]‐cytochalasin D the distribution of the radioactivity originating from incorporated [4′‐3H, U‐14C]‐L‐phenylalanine and [CH3‐14C]‐L‐methionine was determinated. The results demonstrate that the building blocks of cytochalasin D are 1 unit of pheylalanine, 3 units of methionine and acetate units.
Silberioneninduzierte Reaktion von 3‐Chlor‐2‐pyrrolidinocyclohexen mit 1,3‐Dienen. Vorläufige Mitteilung
Authors: Schmid Rudolf , Schmid Hans 
Published: December 2004

Abstract3‐Chloro‐2‐pyrrolidinocyclohexene (3) in the presence of silver tetrafluoroborate in methylene chloride at −60° underwent cycloadditions with various 1,3‐dienes; the resulting iminium tetrafluoroborate salts 4a–8a were hydrolysed to give the bicyclic and tricyclic ketones 4b–8b. The addition reactions can be regarded as [3+4]‐cycloadditions of an intermediate 2‐aminoallyl cation.
13C‐NMR. Spectroscopy of Naturally Occurring Substances. XXXII. Vincaleucoblastine and related alkaloids
Authors: Wenkert Ernest , Hagaman Edward W. , Lal Bansi , Gutowski Gerald E. , Katner Allen S. , Miller Jean C. , Neuss Norbert 
Published: December 2004

AbstractThe total assignment of the 13C‐shifts of the complex Vinica rosea L. alkaloids vincaleucoblastine, leurosidine and leurosine and of a synthetic isomer of the latter is presented. The structure of leurosidine is corrected and a tentative structure for the acid‐catalyzed product of isomerization of leurosine is proposed.
Carotinoidsynthesen über Sulfone; Synthese von β‐Carotin
Authors: Fischli Albert , Mayer Hans 
Published: December 2004

AbstractSulfones, prepared from conjugated arylsulfonyl ylids and allylic halides, eliminate corresponding aryl sulfinates with formation of conjugated polyenes. Using this method β‐carotene (8) has been synthesized.
Über Pterinchemie 53. Mitteilung 1. Zur Konformation von 6‐Methyl‐ und 5,6‐Dimethyl‐5,6,7,8‐terahydropterin in wässeriger Lösung
Authors: Weber Rudolf , Viscontini Max 
Published: December 2004

AbstractNMR.‐Untersuchungen an 6‐Methyl‐ und 5,6‐Dimethyltetrahydropterin in wässeriger Lösung zeigen, dass der Tetrahydropyrazinring in der Halbsessel‐Konformation vorliegt, wobei die Methylgruppe von 6‐Methyl‐tetrahydropterin aus Stabilitätsgründen praktisch ausschliesslich die äquatoriale Stellung einnimmt, während die beiden Methylgruppen von 5,6‐Dimethyl‐tetrahydropterin sich etwa zu gleichen Teilen in axialer und äquatorialer Lage befinden. Durch stark Protonierung (FSO3H) lassen sich die cis‐ und trans‐Isomeren des 5,6‐Dimethyltetrahydropterins im NMR.‐Spektrum nachweisen.
Automatic Geometry Optimization and Vibrational Analysis in External Electric Field: Ethylene
Authors: Pancíř Jiří , Zahradník Rudolf 
Published: December 2004

AbstractStationary points of the INDO energy hypersurface for various orientations of ethylene in external electric fields of the strength F=0, 2, 4, 6, 8 and 10 × 1010 V m−1 were found and their characteristics studied by the force constant matrix analysis. Energies, structural parameters, charges, Wiberg indices and dipole moments are presented. The only stable orientation of the ethylene molecule is that for which the CC bond is parallel to the field direction up to F=6 × 1010 V m−1 (orientation (a) in Fig. 1). Above this value the molecule is structurally unstable and it decomposes to the hydride anion and the C2H3+ cation. Rotational instability was found for two perpendicular orientations of the CC bond with respect to the field vector, in which the field vector was parallel and perpendicular to the molecular plane. Pseudorotations with negative eigenvalues of force constant matrices lead to the stable orientation (a). No stationary points were found when the angle between the CC bond and the field vector was between 0 and 90°. The five longest wavelength vibrational bands are presented for selected orientations and field strengths.
Delayed Fluorescence from Upper Excited Singlet States Sn (n > 1) of the Aromatic Hydrocarbons 1,2‐benzanthracene, fluoranthene, pyrene, and chrysene in methylcyclohexane
Authors: Nickel Bernhard 
Published: December 2004

AbstractDelayed fluorescence (DF.) spectra of 1,2‐benzanthracene, fluoranthene, pyrene, and chrysene in methylcyclohexane were measured at −80° up to the wavenumber corresponding to the energy of two triplets. With all four compounds a weak DF. Sn → S0 from the highest state Sn accessible by triplet‐triplet annihilation (TTA) was found. Lifetimes of Sn calculated (a) from the ratio of the DF's Sn → S0 and S1 → S0 and (b) from the difference in line‐width of the 0,0‐transitions Sn,0 ← S0,0 and S1,0 ← S0,0 agree reasonably well. This indicates that population of the highest accessible excited singlet state is the dominating primary process in the excited singlet channel of TTA. There is no evidence for excimer formation being the first step in TTA. DF. spectra extend up to the energy of two triplets. With pyrene the intensity distribution in the hot‐band region of the DF. S2 → S0 suggests that in TTA the same vibrational selection rules are valid as in one‐photon absorption S2 ← S0 and that vibrational relaxation within the S2 manifold is slow compared with internal conversion S2 ↝ S1. The experimental technique is described in detail and experimental difficulties arising from impurities and photoproduct formation are discussed.
What is the ‘Solvent’ effect on the electronic spectra of a solute in a polymer matrix?
Authors: Schmidt Erika , Loeliger Hans , Zürcher René 
Published: December 2004

AbstractThe theory of solvent‐induced shifts of the absorption and fluorescence band spectra of a solute is well known and has been tested for a multitude of systems. However, there are only few applications to polymers. By a direct comparison of the spectral shifts in liquid solvents with those in polymers it is possible to determine the microenvironment of the solutes in polymers within the frame of this theory. Polyethylene terephthalate as fabric and film was chosen as model polymer. The spectral shifts of 15 fluorescing solutes in this polymer as well as in 10 solvents with widely differing refractive indices n and permittivities ϵ were measured and fitted to the equations given by the theory of the solvent effect. It is found that interactions with the permanent dipoles of polyethylene terephthalate may be neglected within the limits of accuracy attainable for this polymer and the chosen solutes. Dispersion forces dominate the solvent effect. The refractive indices effective at the site of the solute molecules are n = 1.66 for the fabric and n = 1.70 for the film.
Umwandlung der diastereomeren 12‐ und 6‐gliedrigen 1‐Acetyl‐2‐methyl‐1‐cycloalkanole in 1‐Äthinyl‐2‐methyl‐1‐cycloalkene
Authors: Karpf Martin , Walton David , Dreiding André S. 
Published: December 2004

Conversion of the Diastereoisomeric 12‐and 6‐membered 1‐Acetyl‐2‐methyl‐1‐cycloalkanols to 1‐Ethynyl‐2‐methyl‐1‐cycloalkenesThis paper is concerned primarily with a derivation of the E‐configuration of 1‐ethynyl‐2‐methyl‐1‐cyclododecene (10), which plays a role in mechanistic considerations on a method for ring expansion by 3 carbon atoms described in apreceding paper [1]. The derivation is based on an argument using the results of the dehydration of trans‐1‐acetyl‐1‐2‐methyl‐1‐cyclododecanol (4) to 10 with phosphorus oxychloride and pyridine. That this dehydration is stereospecific can be concluded from its regiospecificity since the cis‐hydroxyketone 3 dehydrates mainly to 1‐ethynyl‐12‐methyl‐1‐cyclododecene (mixture of stereoisomers 11 and 12). An x‐ray analysis shows the indicated configurations of the two hydroxyketones 3 and 4.The direction (anti) of the stereospecificity of the double bond introduction during the 4→10 conversion is deduced from the similarity of the behaviour of the two stereoisomeric 1‐acetyl‐2‐methyl‐1‐cyclohexanols 8 and 9 under the same conditions and from mechanistic considerations, which make it likeley that the anti‐elimination behaviour observed in the 6‐membered system has not changed over to a syn‐elimination behaviour in the 12‐membered system. The configurations of the two 6‐membered hydroxyketones 8 and 9 correspond to those of the precursor1‐ethynyl‐2‐methyl‐1‐cyclohexanols 6 and 7, which were clarified with the help of 13C‐NMR.‐spectral coupling observations.It is of interest that the hydroxyketones 3, 4, 8 and 9 react with phosphorus oxychloride and pyridine so as to introduce both a double and a triple bond. It is probable that the double bond is introduced first, inasmuch as the triple bond is not introduced in the absence of activation of the hydroxyl group, as for instance in acetylcyclohexane. This can be used as an argument that the conversion of the acetyl to an ethynyl group in 3, 4, 8 and 9 does not affect the stereospecificity of the dehydration which introduces the ring double bond.1‐Acetyl‐2‐methyl‐1‐cyclododecene (24), a previously isolated compound with pleasant odor, was synthesized by hydration of 10. This furnishes an argument for the E‐configuration of 24.
The stereospecific synthesis of all four stereoisomers of 2‐amino‐6‐phenoxy‐cyclohexanol,
Authors: Lier Edouard , Berthold Richard , Troxler Franz 
Published: December 2004

AbstractEpoxidation of 3‐phenoxycyclohexene 5 with m‐chloro‐perbenzoic acid gave 6 and 7 in a ratio of 9:1. These two epoxides were heated with a series of amines to give the aminophenoxycyclohexanol derivatives 1 and 2 respectively; in all cases the reaction was regio‐ and stereospecific. Two methods based on the principle of neighbouring group participation were developed to synthesize the cis‐amino alcohols 3 and 4. In the first, the hydroxy group was used to introduce an amine function at the vicinal carbon atom. In the second method, the amino group served as the point of reference and the configuration of the adjacent alcohol function was inverted.
Der massenspektrometrische Zerfall isomerer Diacetamido‐cyclo‐hexane, ihrer N‐Phenäthyl‐Derivate und Bis (acetamidomethyl)cyclohexane. 32. Mitteilung über massenspektrometrische Untersuchungen,,
Authors: Süess Hans , Hesse Manfred 
Published: December 2004

The Mass Spectral Decomposition of Isomeric Diacetamido‐cyclohexanes, their N‐Phenethyl‐Derivatives and Bis(acetamidomethyl)cyclohexanesIn the mass spectra of the six isomeric diacetamidocyclohexanes 2‐‐4 (cis and trans each, Scheme 2) as well as of the six isomeric bis(acetamidomethyl)cyclohexanes 6‐‐8 (cis and trans each, Scheme 5) are clear differences between the constitutional isomers, whereas cis/trans isomers show very similar spectra. The lack of stereospecific fragmentations is explained by loss of configurational integrity of the molecular ion before fragmentation.However, the mass spectral fragmentation of epimeric diamidocyclohexanes becomes very stereospecific by the introduction of a phenethyl group on one of the nitrogen atoms: this group avoids epimerization of the molecular ion prior to fragmentation. In the N‐phenethyl derivatives 10, 11, 13 and 14 (Scheme 8) the typical fragmentations of the cis‐isomer after loss of ·C7H7 from the molecular ion are the elimination of CH2CO by formation of cyclic ions, and the loss of p‐toluenesulfonic acid or benzoic acid, respectively, with subsequent elimination of CH3CN (Scheme 9). In the trans‐isomer the typical fragmentations are the loss of the side chain bearing a tertiary nitrogen atom, and the elimination of the tosyl or benzoyl radical, respectively, with subsequent loss of CH3CONH2 (Scheme 10).
Rhodium‐Catalyzed Deuterioformylation of 3‐Methyl‐1‐pentene
Authors: Stefani Annibale , Tatone Dante , Pino Piero 
Published: December 2004

Abstract3‐Methyl‐1‐pentene was deuterioformylated in the presence of rhodium‐catalyst. The extent of attack on each face of the olefin was evaluated from the diastereomeric composition of both positional isomers obtained as the products. An overall preferred attack on the si‐si face of the (S)‐enantiomer, and on the re‐re face of the (R)‐enantiomer was found.
Azimine. III. Kristallstruktur von (1E, 2Z)‐ und (1Z, 2E)‐2, 3‐Dimethyl‐1‐phthalimido‐azimin,
Authors: Moor Robert , Grieb Rita , Niggli Alfred , Hoesch Lienhard , Dreiding André S. 
Published: December 2004

Azimines. III.Teilweise vorgetragen in Bern an der Jahresversammlung der Schweizerischen Gesellschaft für Kristallographie, 7.Oktober 1977, und als Autoreferat veröffentlicht [2].

Crystal structure of (1E,2Z)‐ and (1Z,2E)‐2,3‐dimethyl‐1‐phthalimido‐azimine

Teilweise aus der Diplomarbeit von R. M., ETH Zürich 1977.
The structures of two diastereoisomeric 2,3‐dimethyl‐1‐phthalimido‐azimines, obtained by addition of phthalimido‐nitrene to (E)‐azomethane, have been determined by X‐ray analysis. The major adduct 2a forms rhombic (space group Cmc21), the minor one 2b triclinic crystals (space group Pl). The molecular structures of 2a and 2b in the crystal exhibit several interesting features: (1) The azimines 2a and 2b are true dipolar systems with a coplanar skeleton and with bond angles of about 120°. Thus both azimine N,N bonds are potentially stereogenic centers; (2) 2a and 2b differ in configuration at both of these centers: 2a has
Sterols with Cyclopropane‐Containing Side Chains: Synthesis and Acid Isomerization
Authors: Tarchini Claudio , Rohmer Michel , Djerassi Carl 
Published: December 2004

AbstractTo test the eventual involvement of sterols with a cyclopropane containing side chain in bio‐methylation processes, 24,25‐methanocholest‐5‐en‐3β‐ol (5) and 24,25‐methano‐26‐methylcholest‐5‐en‐3β‐ol (6) were synthesized. Together with the naturally occurring cyclopropane petrosterol (1), they were submitted to acid isomerization to provide chemical models for some of their potential metabolites.
Heterocyclic Spiro‐naphthalenones. Part III. Synthesis and reactions of some spiro [naphthalene‐1,2′‐pyrrolidin]‐2‐ones and spiro [naphthalene‐2,2′‐pyrrolidin]‐1‐ones
Authors: Berney Daniel , Schuh Karlheinz 
Published: December 2004

AbstractThe spironaphthalen‐2‐ones 2, 10 and 18 were prepared by N‐bromosuccinimide (NBS) oxidation of 1, 9 and 17 respectively, whereas spironaphthalen‐1‐ones 24 and 25 were obtained by treating 23 with NBS.The stereoisomeric reduction products 29, 30 and 32 obtained from 24 and 25, gave the pentacyclic compound 33 on treatment with polyphosphoric acid.
Application de la réaction de Wittig à la synthèse de dérivés de bromoénosuloses et d'esters bromoénuroniques. Note de laboratoire
Authors: Tronchet Jean M. J. , Martin Olivier R. , Zumwald Jean‐Bernard 
Published: December 2004

Use of the Wittig reaction for the synthesis of derivatives of bromoenosuloses and bromoenuronic estersTreatment of 3‐O‐benzyl (or 3‐O‐methyl)‐1, 2‐O‐isopropylidene‐α‐D‐xylo‐pentodialdo‐1, 4‐furanoses (2 or 1) with acetylbromomethylidenetriphenylphosphorane (3), benzoylbromomethylidenetriphenylphosphorane (4) or bromoethoxycarbonylmethylidenetriphenylphosphorane (5) gave in good to excellent yields the expected enose (6‐‐11). In all cases but one (8 where some 10% of the E‐isomer was formed) the reaction led to the exclusive formation of the Z‐isomer whose configuration was established by NMR.
Photochemische Reaktionen 113. Mitteilung [1]. Zur Photospaltung konjugierter γ, δ‐Epoxyenone: UV.‐Bestrahlung von 5, 6‐Epoxy‐3,4‐didehydro‐5,6‐dihydro‐β‐jonon
Authors: Murato Kazuo , Wolf Hans Richard , Jeger Oskar 
Published: December 2004

The Photoinduced Cleavage of Conjugated γ, δ‐Epoxyenones: UV.‐Irradiation of 5,6‐Epoxy‐3, 4‐didehydro‐5,6‐dihydro‐β‐iononeOn 1n, π*‐excitation (λ ≥ 347 nm) in pentane or CClF2CFCl2 (E)‐1 is isomerized to the dihydrofurane (E/Z)‐2 as well to the ethers 3 and 5. Besides these products the isomeric cyclopropane derivative (E)‐4 and the acetal 6 are obtained in methanol. The detection of 6 indicates the formation of an intermediate ketoniumylide a which may give 6 by addition of methanol. − On 1π, π*‐excitation (λ=254 nm) in acetonitrile‐d3, CClF2CFCl2 or pentane (E)‐1 yields almost exclusively (E)‐2. In methanol 6 is obtained in addition to (E/Z)‐2, but no (E)‐4 and 5 is formed.
Action du cyanure mercurique sur quelques halogénures de désoxy‐3‐trifluoroacétamido‐3‐D‐ribofurannosyle. Note de laboratoire
Authors: Tronchet par Jean M. J. , Grouiller Annie , Martin Olivier R. 
Published: December 2004

Reactions of Some 3‐Deoxy‐3‐trifluoroacetamido‐D‐ribofuranosyl Halides with Mercuric CyanideThe expected 2,5‐anhydro‐D‐allononitrile 11 was obtained when the 2‐O‐benzoyl‐3‐deoxy‐3‐trifluoroacetamido‐D‐ribofuranosyl bromide reacted with mercuric cyanide, whereas the isomeric 1,2‐O (1‐cyanoethylidene) derivative was formed from the 2‐O‐acetylated halide; no reaction occurred when the halide was 2‐O‐p‐nitrobenzoylated.
Zur Synthese sulfonierter Derivate von 4‐ und 5‐Aminoindan
Authors: Courtin Alfred 
Published: December 2004

On the Synthesis of Sulfonated Derivatives of 4‐ and 5‐AminoindanBaking the hydrogensulfate salt of 4‐aminoindan (1) and 5‐aminoindan (2) led, respectively, to 4‐aminoindan‐7‐sulfonic acid (3) and 5‐aminoindan‐6‐sulfonic acid (4). Acid 4 was also obtained by direct sulfonation of 2. 4‐Aminoindan‐6‐sulfonic acid (5) and 6‐aminoindan‐4‐sulfonic acid (6) were prepared by sulfonation of 4‐nitroindan (7) and 5‐nitroindan (9), respectively, to 4‐nitroindan‐6‐sulfonic acid (8) and 6‐nitroindan‐4‐sulfonic acid (10), followed by a Béchamp‐reduction. Treatment of 1 with amidosulfuric acid gave 3, whereas the same reaction with 2 led to a mixture of 4 and 5‐aminoindan‐4‐sulfonic acid (11). Independent synthesis of 11 was achieved by the following sequence of reactions: sulfur dioxide treatment of the diazonium chloride derived from 4‐amino‐5‐nitrodan (13) gave 5‐nitroindan‐4‐sulfonyl chloride (14); hydrolysis to 5‐nitroindan‐4‐sulfonic acid (15), and final reduction. The 4‐aminoindan‐5‐sulfonic acid (16) was synthesized by treatment of 4‐amino‐7‐bromoindan (18) with amidosulfuric acid to give 4‐amino‐7‐bromoindan‐5‐sulfonic acid (19) followed by hydrogenolysis. Sulfonation of 4‐acetyl‐amino‐7‐bromoindan (17) with oleum followed by hydrolysis led to 7‐amino‐4‐bromoindan‐5‐sulfonic acid (20), the structure of which was confirmed by reductive dehalogenation to 5.