bluuebunny/crossref_metadata_2025 huggingface dataset:
Sannamycin‐type aminoglycoside antibiotics of natural and non‐natural (mirror‐image) configuration — total syntheses and biological activity
Authors: Ludin Christian , Weller Thomas , Seitz Bernhard , Meier Walter , Erbeck Silke , Hoenke Christoph , Krieger Richard , Keller Manfred , Knothe Lothar , Pelz Klaus , Wittmer Annette , Prinzbach Horst
Published: July 2007

Sets of variously protected purpurosamine/2‐epi‐purpurosamine‐type glycosyl donors (O‐acetates) and sannamine‐type glycosyl acceptors were coupled as racemates and pure enantiomers, according to a modified Koenigs‐Knorr procedure with TMSOTf as promotor. The α anomers isolated from the respective mixtures of glycosides (yields varying between 51% and 91%, α:β anomeric ratios between 1.5:1 and 13:1, α:α′ diastereomeric ratios between 1:1 and 1:1.5) were transformed through standard protection/deprotection and glycidation measures into 6′‐des(N‐methyl)sannamycins A (1, 1′, 2, 2′) and B (37, 37′), 2′‐epi‐6′‐des(N‐methyl)sannamycins (3, 3′), the enantiomeric sannamycins A and B (ent‐4)/ (ent‐40), the diastereomers (ent‐4′)/(ent‐40′), and the enantiomeric 2′‐epi‐sannamycin A (ent‐5)/(ent‐β‐5). For one of the fluorinated glycosides (α‐26′), featuring a somewhat unusual aglycon conformation, an X‐ray structural analysis was performed. In explorative biological tests, the naturally configurated glycosides1and3showed limited,2a rather broad activity against a number of pathogenic microorganisms. Yet, none of the glycosides with non‐natural configuration was found to be active.
Chiral polymethine dyes, IV. Synthesis, absolute configuration, spectroscopic and chiroptical properties of chiral tri‐ and pentamethinium cyanine dyes with 1,2,3,4‐tetrahydro‐6‐methylquinolyl end groups
Authors: Reichardt Christian , Harms Klaus , Kinzel Manuela , Schäfer Gerhard , Stein Jörg , Wočadlo Sigrid
Published: July 2007

We have repeated and significantly improved the syntheses of the symmetrical tri‐ and pentamethinium cyanine dyes 10 and 11 in their monochiral forms (10a, b; 11a, b) and in the meso form (11d) as well as of the unsymmetrical monochiral pentamethinium cyanine dye 14a, first realized by König and Langbein in 1928. Their spectroscopic properties have been studied for the first time. The monochiral starting compounds 4a, b, and hence all related monochiral polymethine dyes, have been obtained with high enantiomeric excess (e.e. >99%) by recrystallization of their diastereomeric 3‐bromocamphor‐8‐sulfonates 6a, b. The absolute configuration of 4a, b, and thus the absolute configuration of all monochiral polymethine dyes derived from 4a, b, has been determined by X‐ray structural analyses of the tetrahydroquinolinium perchlorate 7a and the pentamethinium bromide 11a. Partial hydrolysis of the monochiral pentamethinium dye 11a gave the monochiral pentamethine merocyanine dye 12a, which was allowed to react either with 13 to yield the unsymmetrical monochiral pentamethinium dye 14a or with monochiral 7b to afford the symmetrical achiral meso‐pentamethinium dye 11d. The pentamethinium cyanine dyes 11a, b, d and 14a were used to examine the proposed additivity in calculating the overall molecular optical rotation of 11a, b (Table 1).
Phosphanalkylene, 54. Synthese und Eigenschaften von Bis(trimethylsilyl)keton
Authors: Bestmann Hans Jürgen , Haas Wolfgang , Witzgall Konrad , Ricci Alfredo , Lazzari Dario , Degl'Innocenti Alessandro , Seconi Giancarlo , Dembech Pasquale
Published: July 2007

Phosphane Alkylenes, 54, – Synthesis and Properties of Bis(trimethylsilyl) Ketone

The synthesis of the bis(trimethylsilyl) ketone (1b) by oxydation of [bis(trimethylsilyl)methylene]triphenylphosphorane (3) is described. The IR, UV, NMR, and PE spectra as well as the cyclovoltagram of this compound are discussed and compared with those of di‐tert‐butyl ketone (13) and tert‐butyl‐trimethylsilyl ketone (10).
Electrophile‐induced cyclizations of silyl‐substituted 4‐alken‐1‐ols
Authors: Adiwidjaja Gunadi , Flörke H. , Kirschning A. , Schauman Ernst
Published: July 2007

Silyl‐substituted 4‐alken‐1‐ols cyclize in the presence of a wide range of electrophilic reagents to give substituted tetra‐hydrofurans. The silyl group accelerates ring closure by its β‐effect and its position determines the efficiency of stereo‐control. Thus, a vinylic silyl group as in 1, 3‐9 gives mixtures of 2,5‐disubstituted tetrahydrofurans 2, 10‐21, favoring formation of the trans isomer. In contrast, an allylic silyl group as in 28‐30 exerts a high degree of stereocontrol, generally affording 2,3‐trans‐disubstituted tetrahydrofurans 31‐36.
Synthesis of bridgehead polycyclic 1,2‐diamines and 2‐amino alcohol derivatives as Rigid acetylcholine analogs
Authors: Camps Pelayo , Font‐Bardia Mercè , Muñoz‐Torrero Diego , Solans Xavier
Published: July 2007

Oxidation of dioxime 2a with NBS gave 3 and 4. A chair‐boat conformation has been established for 3 by X‐ray diffraction analysis, while 4 seems to exist in a chair‐chair conformation on the basis of NMR data. m‐Chloroperbenzoic acid oxidation of dioximes 2 gave polycyclic dinitro compounds 7. In some oxidations of 2a, nitroso dimer 8 was isolated, its structure being established by X‐ray diffraction analysis. Reduction of 7 with aluminium amalgam gave in good yields diamines 6, that were also obtained by reductive coupling from dioximes 2. Amino alcohols 14 were obtained by reductive coupling from monooximes 11. While 11a could be obtained in pure form from diketone 1a via 9a and 10a; hydrolysis of 10b to 11b failed. Azapolycyclic compounds 12 were obtained by hydrolysis of 10. Amino alcohol 14b was more appropriately prepared by reduction of nitro alcohol 15 obtained together with 7b by m‐chloroperbenzoic acid oxidation of a mixture containing monooxime 11b and dioxime 2b. From the oxidation of a mixture containing 11a, nitro ketone 16 was isolated in low yield. Amino alcohols 14 and diamines 6 were also characterized as cyclic carbamates 13 or ureas 5. Rigid analogs of acetylcholine 20 and 21 were obtained from 14 by standard procedures, compounds 17 and 18 being detected as intermediates. Neither muscarinic nor antiacetyl‐cholinesterase activity has been observed for compounds 20 and 21.
Synthese und Konformation von Hexahydro‐isochino[3,2‐a][2]benzazepinen des B‐Homoberbin‐Typs
Authors: Meise Werner , Zlotos Darius , Jansen Martin , Zoche Nicola
Published: July 2007

Synthesis and Conformation of Hexahydro‐isoquino[3,2‐a][2]benzazepines of the B‐Homoberbine Type

The two‐step synthesis of the hexahydro‐isoquino[3,2‐a][2]‐benzazepines („B‐homoberbines”︁) 4b‐e is described. The main and some further products of the Bischler‐Napieralski reaction of hydroxyamide 3c were isolated and identified. The conformation of the B‐homoberbines was investigated by X‐ray analysis, spectroscopic methods and dehydrogenation with mercury(II) acetate.
Maravuic acid, a new seco‐labdane diterpene from Croton matourensis
Authors: Schneider Christiane , Breitmaier Eberhard , de C. Bayma Joaquim , de Franca Luiz F. , Kneifel Helmut , Krebs Hans‐Christoph
Published: July 2007

A new seco‐labdane diterpene, maravuic acid, has been isolated by supercritical fluid extraction using CO2 from the bark of Croton matourensis Aubl. (Euphorbiaceae). Its structure was elucidated by one and two dimensional NMR methods as (12E)‐3,4‐seco‐labda‐4(18),8(20),12,14‐tetraen‐3‐oic acid 2.
Syntheses and structures of 3,7‐substituted barbaralanes
Authors: Quast Helmut , Witzel Martina , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg
Published: July 2007

Short and efficient syntheses of the barbaralanes 2e‐h are reported. Meerwein's diketone 9 is converted into the bis(vinyl sulphide) 10 by the action of 4‐chlorothiophenol in the presence of titanium(IV) chloride and triethylamine. Oxidation of 10 with sodium perborate in acetic acid affords the bis(vinyl sulphone) 11 which is treated with potassium cyanide supported on aluminium oxide to yield the unsaturated dinitrile 8. Bromination of 8 with N‐bromosuccinimide and subsequent reductive cyclisation of the resulting exo,exo dibromodinitrile 13 with the zinc‐copper couple furnish 3,7‐dicyanobarbaralane (2e) in 53% overall yield based on 9. – Treatment of dinitrile 8 with hydrochloric acid in boiling methanol followed by hydrolysis of the intermediate Pinner salt yields the dimethyl dicarboxylate 14 which is brominated to afford the exo,exo dibromo diester 15. Reductive cyclisation of 15 gives rise to the formation of dimethyl 3,7‐barbaralanedicarboxylate (2f) in 49% overall yield based on 9. – Bicyclo[3.3.1]nonane‐3,7‐dione (7) is converted into a mixture of the bis(vinyl sulphones) C2‐ and Cs‐17 (1:1) as described for 9 → 11. Bromination of this mixture yields a single exo,exo dibromo compound 18 which is cyclised by the zinccopper couple to afford 3,7‐bis(phenylsulphonyl)barbaralane (2g) in 56% overall yield based on 7. – The known phenyl‐2‐oxaadamantanol 21a is cleaved by the action of boron trifluoride and acetic anhydride to yield the bicyclo[3.3.1]none‐none 22. The difluoroboron complex 23 is obtained under more rigorous conditions. Addition of phenylcerium(III) chloride to 22 followed by dehydration of the endo alcohol 24 yields the diphenyldiene 25. Bromination of 25 and subsequent reductive cyclisation of the exo,exo dibromodiphenyldiene 26 furnish 3,7‐diphenylbarbaralane (2h) which is isolated by preparative reversed‐phase chromatography in 50% overall yield based on 7. – The configurations and conformations in the crystals are elucidated by X‐ray diffraction analyses for the bicyclo[3.3.1]nonane derivatives 7, 13, 15, 18, 22–24, and 26 and the barbaralanes 2e‐g. In the solid state, 2e and f exist as pairs of rapidly rearranging nonequivalent valence tautomers while the atomic distances observed for 2g indicate the presence of a single nonrearranging valence tautomer.
Antibiotics from gliding bacteria, LXV. Synthesis of soraphen analogues by substitution of the phenyl‐C‐17 ring segment of soraphen A1α
Authors: Schummer Dietmar , Jahn Thorsten , Höfle Gerhard
Published: July 2007

The partial synthesis of 11 analogues of soraphen A1α (1) is described. Reductive lactone ring cleavage, transformation into (17R,S)‐soraphenic acid 10 and cyclization provided unnatural 17‐epi‐soraphen A1α (12). Removal of the phenyl‐C‐17 ring segment of 1 by cleavage of the lactone moiety and the C‐16/C‐17 bond gave the aldehyde 16 as central intermediate. After homologation of 16, introduction of a new C‐17 substituent R or H, and cyclization of the lactone ring, the soraphen analogues butyl‐, thienyl‐, and tolylsoraphen 2b, d, e and 22b, d, e and the desphenylsoraphen 2a were obtained. The ring‐contracted soraphen analogues norsoraphen 29 and 30 and desphenylnorsoraphen 31 were synthesized by introduction of a phenyl group or reduction of the intermediate aldehyde 23 followed by cyclization to the lactone. The biological activity of the soraphen analogues against Candida albicans was determined. Compared to the natural product, all analogues exhibit reduced activity. The activity of the analogues strongly depends upon the nature of the substituent R, the configuration at C‐17, and the ring size.
Halogenated indocyanines: Synthesis, conformational behavior, and light absorption
Authors: Grahn Walter , Johannes Hans‐Hermann , Rheinheimer Joachim , Knieriem Burkhard , Würthwein Ernst‐Ulrich
Published: July 2007

The reactions of the indocyanine 1a and its corresponding 1,3‐diaminoallene 2a with N‐halodiorganosulfonimides 3 or molecular halogen result in the formation of the four chain‐halogenated monomethine cyanines 5a‐d. With an excess of the halogenating agent not only the chain but also the end groups are halogenated affording the monomethines 6 and 7. The preferred conformations, UV/Vis absorptions, and electron densities of the cyanines were calculated by AM1 and PPP methods and experimentally investigated using NMR (DNMR, NOE) as well as UV/Vis spectroscopy.
Marine bacteria, VIII. Maremycin A and B, new diketopiperazines from a marine Streptomyces sp.
Authors: Balk‐Bindseil Wiebke , Helmke Elisabeth , Weyland Horst , Laatsch Hartmut
Published: July 2007

In the culture broth of the marine Streptomyces sp. B 9173 the two novel diketopiperazines maremycin A (1) and B (2) were detected by chemical screening. Their structures were elucidated and confirmed by the synthesis of the oxindole derivative 4.
Spiro units as building blocks in thermotropic liquid crystals: Synthesis and physical properties of terminally substituted spiro[5.5]undecanes
Authors: Schmidt Wolfgang , Vögtle Fritz , Poetsch Eike
Published: July 2007

A number of terminally substituted spiranes were prepared from 9‐pentyl‐3‐spiro[5.5]undecanone (7), which was obtained in a five‐step synthesis starting from 4‐pentylcyclohexanone (1), using an intramolecular cyclisation with 4‐toluenesulfonylmethyl isocyanide (TosMIC) as a key step. By a comparison of the physical data of the new spiro[5.5]undecane derivatives I with those of several well‐known, analogous substituted compounds – solely differing in their central building unit – conclusions regarding the effects of the spiro ring system on its mesogenic potential are drawn.
Synthesis of some naturally occurring drimane and dinorlabdane derivatives
Authors: Weyerstahl Peter , Schwieger Ralf , Schwope Ina , Hashem Md. Abul
Published: July 2007

The naturally occurring (ex Hedychium acuminatum) compounds drim‐8(12)‐ene (1), albicanal (4), (E)‐15,16‐dinorlabda‐8(17), 11‐dien‐13‐one (5), and (E)‐15, 16‐dinorlabda‐8(17), 12‐dien‐14‐al (9), were prepared as racemates by starting from the synthetically available rac‐albicanol (2). – The Nozaki reaction of the trimethyldecalone 10 yields 11‐nordrim‐8‐en‐12‐al (11) and its Δ7 regioisomer 12.
Tetra(2,6‐dichlorophenyl)porphyrin — a superior sensitiser for the singlet‐oxygen ene reaction (Schenck reaction)
Authors: Quast Helmut , Dietz Thomas , Witzel Alexander
Published: July 2007

The very useful singlet‐oxygen ene reaction of reluctant alkenes, e.g.1, 5, 7, 8, and, in particular, the mono(allyl hydroperoxides)10and11, is handicapped by the instability of the sensitiser TPP. A comparative study of TPP, TPFPP, and TDCPP in the singlet‐oxygen ene reaction of these alkenes shows that 1) the persistence increases in the order TPP < TPFPP < TDCPP, rendering TDCPP the sensitiser of choice for the generation of singlet‐oxygen in non‐polar solvents, 2) the persistence of the tetraarylporphyrins decreases in the presence of an alkene, 3) this decrease strongly depends on the nature of the alkene, being most pronounced in the case of cyclohexene. These results are interpreted in terms of unknown substrate‐derived species which induce oxidative destruction of the tetraarylporphyrins. Alternatively, abstraction of allylic hydrogen atoms from the alkenes by the excited sensitisers may give rise to the observed substrate‐dependent photobleaching. – Because the singlet‐oxygen ene reaction is the key step of a 1,2‐carbonyl transposition with concomitant dehydrogenation, the scope and usefulness of this sequence are distinctly improved.
Enzymes in organic synthesis, 25. Lipase‐catalyzed sequential esterification of (±)‐2‐methylbutanedioic anhydride — a biocatalytical access to an enantiomerically pure 1‐monoester of (S)‐2‐methylbutanedioic acid
Authors: Ozegowski Rüdiger , Kunath Annamarie , Schick Hans
Published: July 2007

The preparation of enantiomerically pure 1‐(2‐methylpropyl) 4‐hydrogen (S)‐2‐methylbutanedioate (ent‐3) by an enzyme‐catalyzed sequential esterification of (±)‐2‐methylbutanedioic anhydride (rac‐1) demands two different enzymes. Lipozyme, a lipase from Mucor miehei, was used for the alcoholysis of rac‐1 to a mixture of the isomeric monoesters 2/ent‐2 and 3/ent‐3, whereas Novozym 435, a lipase from Candida antarctica, was required for the enantioselective conversion of a mixture of 3 and ent‐3 into the easily separable neutral diester 4 and the acidic monoester ent‐3, which thus was obtained in a yield of 26% with an enantiomeric excess of 99%. ent‐3 was reduced by LiBH4 to (S)‐3‐methylbutan‐4‐olide (ent‐10), a versatile chiral intermediate.
Ethyl N‐(diphenylmethylene)glycinate as anionic glycine equivalent transition metal mediated preparation of bicyclic and tricyclic α,α‐disubstituted α‐amino acids and derivatives
Authors: Moreno‐Mañas Marcial , Pleixats Roser , Roglans Anna
Published: July 2007

Synthetic approaches to bicyclic and tricyclic α,α‐disubstituted α‐amino acids and derivatives 6, 8, 10, 12, 13, 21, 22, 23, 24, 28, 30, and 31 are presented. Methyl acetoacetate, ethyl nitroacetate, and ethyl N‐(diphenylmethylene)glycinate are compared as anionic glycine equivalents. Palladium‐induced reductive couplings, Diels‐Alder and Pauson‐Khand reactions are used in the cyclisation steps.
Electron‐transfer‐catalyzed reactions, 7. Aminium salt‐initiated oxygenation of ketenes — formation of succinic anhydrides
Authors: Schmittel Michael , von Seggern Heinke
Published: July 2007

The aminium salt‐initiated oxygenation of ketenes 1a and 1b with molecular oxygen afforded in an unprecedented reaction mode the succinic anhydrides 2 and 3 within a few minutes at 0°C. From mechanistic investigations it is inferred, that the regioselective 1,3‐dipolar cycloaddition of an intermediate α‐lactone, independently trapped by cycloaddition to hexafluoroacetone, to the ketene constitutes the final step of the reaction sequence. Surprisingly, the oxygenation reaction occurred even when the reaction was carried out with rigorous exclusion of atmospheric oxygen. Evidence is presented that aminium salts are capable of both storing and activating molecular oxygen with remarkable efficiency, and that the reaction does not proceed via free ketene cation radicals.
Structure‐odor correlation, XXI. Olfactory properties and convenient synthesis of furans and thiophenes related to rose furan and perillene and their isomers
Authors: Weyerstahl Peter , Schenk Anja , Marschall Helga
Published: July 2007

Starting from 3‐bromofuran (1) or 3‐bromothiophene (2) via alkylation in 2‐position (→ 3–8) followed by the corresponding second alkylation in 3‐position, we obtained rose furan (9), rose thiophene (10), and their analogs 11–16. From the α,β‐unsaturated esters 17–20 by hydrogenation (→ 21–24), DIBAH reduction (→ 25–28), and Wittig reaction, perillene (29), thioperillene (30), and their analogs 29–36 were obtained. Olfactory evaluation showed that the difference between the furans and thiophene derivatives is remarkably small, particularly for perillene (29) compared with thioperillene (30), and their analogs. Also the influence of position and structure of the side chain is lower than expected within the compared compounds 9–36.
Synthesis of 5,8‐dimethoxy‐2(1H)‐quinolinones by intramolecular Wittig reaction
Authors: Ferrer Pedro , Avendaño Carmen , Söllhuber Mónica
Published: July 2007

The title compounds 12, which are key intermediates for antitumoral diazaquinomycin A analogues, are obtained by intramolecular Wittig reaction of 1‐[3′,6′‐dimethoxy‐2′‐(α‐oxoacylamino)phenyl]alkyltriphenylphosphonium salts 11, which are prepared via lithiation of 2′,5′‐dimethoxy‐N‐pivaloylaniline 6. The applicability of this route to polysubstituted 2(1H)‐quinolinones 12 and 17 is examined.
Molecular modeling of saccharides, 8. Selective 2‐O‐benzylation of sucrose: A facile entry to its 2‐deoxy‐ and 2‐keto‐derivatives and to sucrosamine
Authors: Lichtenthaler Frieder W. , Immel Stefan , Pokinskyj Peter
Published: July 2007

Generation of the molecular electrostatic potential (MEP) profiles, in color‐coded form, on the solvent‐accessible contact surfaces of the two main conformations that sucrose adopts in vacuo as well as in aprotic solvents (e.g. DMF), clearly shows the secondary glucosyl‐2‐OH to be the most electropositive of the altogether eight hydroxyl groups–conceivably due to the persistence of an intramolecular hydrogen bond of the 2g‐O…︁HO‐1f type. The notion that the 2g‐OH is accordingly the hydroxyl group most readily deprotonated in aprotic solvents, and that the resulting sucrose 2g‐O‐alkoxide is the one best stabilized by intramolecular hydrogen bonding, received ample substantiation by smoothly achieving a highly regioselective (>80%) 2g‐O‐benzylation in DMF with NaH/benzyl bromide. The resulting 2g‐O‐benzyl‐sucrose (2)– minor products being the 1f‐O‐ (3) and 3f‐O‐isomers (4)– was converted, by acetylation and hydrogenolysis into the 2g‐OH‐free sucrose heptaacetate 6, isolable in crystalline form in 42% yield based on sucrose, thus opening up a ready entry to 2g‐O‐modified derivatives: 2‐deoxy‐sucrose (12) via radical deoxygenation of a 2g‐O‐thiocarbamate, 2‐keto‐sucrose perbenzoate 7 via PDC oxidation, or N‐acetyl‐sucrosamine 14 and its manno‐analog 16 through oximation of 7 and subsequent borane reduction.
Asymmetric synthesis of chiral, nonracemic dialkyl α‐hydroxyarylmethyl‐and α‐, β‐ and γ‐hydroxyalkylphosphonates from keto phosphonates
Authors: Meier Chris , Laux Wolfgang H. G. , Bats Jan W.
Published: July 2007

The enantioselective synthesis of α‐hydroxyarylmethylphosphonates 2a‐p by the oxazaborolidine‐catalyzed reduction of α‐keto phosphonates 1a‐p using different boranes 4a–c was studied in detail. Moderate to good enantioselectivities are found (up to 80% ee) by using the borane‐dimethyl sulfide complex 4a as reducing reagent and the 2‐n‐butyl derivative of the (S)‐5,5‐diphenyl‐3,4‐trimethylene‐1,3,2‐oxazaborolidine catalyst 3b. In contrast, excellent enantiomeric excesses (up to 99% ee) as well as high chemical yields are obtained when catecholborane 4c in combination with low temperature is introduced. Substituent effects on the starting material 1 are discussed with the help of structural information obtained by X‐ray analyses of the benzoylphosphonates 11fγ, 1jγ, and 1nγ. A slight decrease in enantioselectivity was found within the series of α‐, β‐, and γ‐hydroxyalkylphosphonates 6, 8, and 10, respectively. Nevertheless, even these compounds are reduced with enantioselectivities ranging from 68% (10) to 95% (6) by using catecholborane 4c and catalyst 3b. On the other hand, we synthesized the allylic α‐hydroxyphosphonate 12 in 75% chemical yield and with 56% enantiomeric excess by means of this methodology. The reaction has subsequently been applied to the synthesis of α‐hydroxyalkylphosphonates 14a–c, which were obtained with ee values up to 90%. Compounds 14 are useful precursors for the synthesis of the P‐amino acids 15.
α‐Thiotetronic Acids, II. Reactions of γ‐Alkylidene‐α‐Thiotetronic Acids
Authors: Stachel Hans‐Dietrich , Zeitler Klaus
Published: July 2007

The α‐thiotetronic acid 1 reacts with amines predominantly with ring opening to give polyfunctionalized ketones (2) which readily cyclize to α‐tetramic acid amides (4a, b). The reaction of α‐thiotetronate 6 with nucleophiles is more complex, leading to either an open‐chain derivative (8) or formation of an α‐thiotetronic acid amide (3b) or an α‐tetramate (4f). Treatment of 6 with sodium sulfide in air furnishes the salt of the 1,2‐dithiole 10. The dibrominated α‐thiotetronate 13a reacts with N and S nucleophiles predominantly by substitution, leading finally to the bisthiolactones 14 or the thieno‐1,2‐dithioles 17.
Studies on ketoses, 10. Acylation and carbamoylation of D‐fructose: Acyclic, furanoid and pyranoid derivatives and their conformational features
Authors: Lichtenthaler Frieder W. , Klotz Jürgen , Flath Franz‐Josef
Published: July 2007

Acylations of D‐fructose are complicated at several levels. The product distribution is determined not only by the rate of equilibration of the crystalline β‐p‐form in pyridine to the α‐p, β‐f, and α‐f‐tautomers, but also by the distribution of these forms at a given temperature, as well as their individual hydroxyl group. A detailed study of these parameters resulted in the elaboration of new or improved procedures for the practical, straightforward preparation of either acyclic, furanoid, or pyranoid benzoyl and pivaloyl derivatives, as well as cyclocarbamates with 1,2‐spiro‐annelated and 2,3‐bridging oxazolidinone rings. Accordingly, a variety of simple, tautomerically fixed fructose derivatives, most notably those of the α‐p, α‐f and β‐f forms, are now easily accessible for exploitation as versatile enantiopure building blocks. The structures, anomeric configurations and conformations of the various products obtained were determined on the basis of their 1H and 13C NMR data. The furanoid cases required the support of two X‐ray structures: the pentabenzoyl‐α‐D‐fructofuranose (9) which has an E2 conformation, and the 2,3‐cyclocarbamate 25, in which the β‐furanose ring adopts a 5E geometry.
Trapping reactions of sulfenes generated from sulfonic acid derivatives and bases, 1. Cyclopentadiene, methylcyclopentadiene and 1,2,3,4‐tetraphenylcyclopentadiene used as sulfene scavengers. [4 + 2] cycloaddition reactions and sulfonylations
Authors: Opitz Günter , Deißler Michael , Ehlis Thomas , Rieth Karlheinz , Irngartinger Hermann , Ziegler Manfred L. , Nuber Bernhard
Published: July 2007

The bulky sulfenes generated in situ from (+)‐10‐camphor‐, 10‐camphane‐, and 2‐methyl‐2‐phenylpropanesulfonyl chloride (1a–c) and Et3N can be trapped by cyclopentadiene to give the [4 + 2] cycloadducts 6a–c. The mixture of endo‐6a and exo‐6a (no other diastereomers) is formed by complete asymmetric induction. In MeCN solution additionally the 1,3‐di‐ and 1,2,4‐trisulfonylated cyclopentadienides 4a–c and 5a (X‐ray analysis) + 5c were obtained. On acidification, 4a and 5a were transformed into the pentafulvenoid derivatives 8a, 9a, 10a. The reaction of (+)‐10‐camphorsulfonyl chloride (1a)/Et3N with 1,2,3,4‐tetraphenylcyclopentadiene afforded the sulfonylated product 11a, with 2‐methylcyclopentadiene 50% endo‐12a (X‐ray analysis) and 10% exo‐12a. From cyclopentadiene and the more electrophilic cyanosulfene (2e) and mesylsulfene (2f, X = Me), generated in situ from cyanomethanesulfonyl chloride (1e)/Et3N and from mesyl chloride/Et3N, the [4 + 2] cycloadducts 6e and 6g were obtained. Similarly, methanedisulfonyl dichloride (1f, X = Cl)/Et3N afforded stereospecifically by two subsequent [4 + 2] cycloadditions the spirodisulfone 16 (X‐ray analysis).
Cascade reactions with chiral michael acceptors; synthesis of enantiomerically pure tricyclo[3.2.1.02,7]‐ and bicyclo[3.2.1]octanes
Authors: Braun Norbert A. , Klein Iris , Spitzner Dietrich , Vogler Bernhard , Braun Siegmar , Borrmann Horst , Simon Arndt
Published: July 2007

Starting from the easily accesible chiral aldehyde 2, we obtained enantiomerically pure (Z)‐ and (E)‐α,‐chloro‐α,β‐unsaturated esters 4c in good yields by olefination reactions. (Z)‐and (E)‐4c were allowed to react with the kinetically controlled generated lithium dienolate Li‐7 to give the enantiomerically pure tricyclo[3.2.1.02,7]octanes 8 and 9, respectively. The „push‐pull”︁ substituted cyclopropane moiety of 8 was opened to give solely bicyclo[3.2.1]octane 10.
5′,5′‐di‐O‐nucleosyl‐O′‐benzylphosphotriesters as potential prodrugs of 3′‐azido‐2′,3′‐dideoxythymidine‐5′‐monophosphate
Authors: Meier Chris , Habel Lothar W. , Balzarini Jan , De Clercq Eric
Published: July 2007

The synthesis of 5′,5′‐O‐di‐(3′‐azido‐2′,3′‐dideoxythymidinyl)‐O′‐benzylphosphotriesters 1 as potential prodrugs of nucleoside monophosphates is described. The concept is applied to the antiretroviral nucleoside analog 3′‐azido‐2′,3′‐deoxythymidine (AZT) 4. All derivatives 1 were synthesized by reaction of the tetra‐n‐butylammonium salt of di‐AZT‐phosphate 2b with different benzyl bromides or ‐chlorides 9. Compound 2b was obtained by a combination of phosphoamidite/H‐phosphonate chemistry, subsequent oxidation to 2a, and cation exchange. The partition coefficients of 1 in an 1‐octanol/water mixture show that all compounds exhibit a much higher lipophilicity than the parent nucleoside AZT (4). It was also shown, that 1 decomposes spontaneously under mild aqueous basic conditions (phosphate buffer (pH 7.5) and RPMI culture medium containing heat‐deactivated fetal calf serum) releasing selectively the di‐AZT phosphate anion 2. The half‐lives of 1 could be adjusted within a wide range by changing the ring substituents of the benzyl group. Additionally, the mechanism of hydrolysis varies if the substituent is changed from a donor to an acceptor one. The described phosphotriesters 1 exhibit considerable antiviral activity in HIV‐1‐ and HIV‐2‐infected CEM/O cells, whereas no activity was detected in the HIV‐2‐infected thymidine kinase‐deficient CEM cell line. On the other hand, we could not detect any cytotoxicity of the described phosphotriesters. Consequently, compounds 1 should act as prodrugs or depot forms at least of antiviral nucleoside analogs.
EPR Study of the Radical Ions of Aryl‐Substituted Propellanes
Authors: Crockett Rowena , Gescheidt Georg , Dyker Gerald , Körning Jutta
Published: July 2007

The radical anions and the radical cations of 1–3 in which three π systems are connected in three dimensions by a strained propellane spacer were studied by ESR/ENDOR/TRIPLE spectroscopy. The hyperfine data of acenaphthene (4) are compared with those of the fused π systems 5–10. In the relatively persistent radical anions of 1–3, the spin is mainly confined to the two naphthalene moieties. Whereas the radical cation of 2 resembles a naphthalene trimer, the radical cations of intact 1 and 3 cannot be detected. The ESR spectra recorded upon one‐electron oxidation of 1 and 3 are assigned to the radical cations of 9 and 10, respectively, formed by the loss of one naphthalene moiety from the parent molecules.
Zwitterions as Intermediates in 1,3‐Dipolar Cycloadditions of Electrophilic Azides to 2‐Alkylidenetetrahydroimidazoles and 2‐Alkylidenedihydrobenzimidazoles
Authors: Quast Helmut , Ach Manfred , Ivanova Svetlana , Peters Eva‐Maria , Peters Karl , von Schnering Hans Georg
Published: July 2007

Cyclic ketene N,N‐acetals derived from imidazolidine (4a, c) and 2,3‐dihydrobenzimidazole (6a–c) add methanesulphonyl azide (2a) or picryl azide (2f) to afford the zwitterions 5 and 7, respectively. The structure of 7d is elucidated by X‐ray crystallography. Reversibility of formation and thermal stability of the N‐sulphonyl zwitterions depend on the substitution pattern at the carbon atom to which the triazenide moiety is attached: In the case of a pair of geminal methyl groups (5a, 7a) formation is irreversible and decomposition by cyclisation and subsequent reactions occurs above −20°C, while in presence of a single alkyl group (7c, d) these processes require heating to 80°C and are accompanied by partial reversion to 2a and ketene N,N‐acetals (6b, c). Cyclisation of the zwitterions yields intermediate spirocyclic [3 + 2] cycloadducts, which may undergo [3 + 2] cycloreversion into N‐sulphonylimine 13 and diazo compound 14 or extrude molecular nitrogen to furnish ring‐expanded 2‐(sulphonylimino)piperazine derivatives (9, 11).
A Practical Synthesis of Enantiopure (R)‐4‐Hydroxy‐2‐cyclohexen‐1‐one
Authors: Gebauer Olaf , Brückner Reinhard
Published: July 2007

The title compound R‐4a was prepared from (–)‐quinic acid (1) in 6 steps in 18% overall yield (Scheme 3) and with 100% enantiomeric purity (Figure 1). The initiating step is the regio‐ and stereoselective acetalization of the trans‐oriented vicinal OH groups of 1 (+ 5 → 8). Alcohol R‐4a can be protected as the 2‐ethoxyethyl ether R‐4e (78%).
Photochemical Behavior of Doubly Bridged Dewar Benzenes – Synthesis of Prismanes
Authors: Gleiter Rolf , Ohlbach Frank , Haberhauer Gebhard , Irngartinger Hermann , Oeser Thomas
Published: July 2007

In this paper we report on the photochemistry of Dewar benzenes bridged at the 1,4‐ and 5,6‐positions and substituted at the 2,3‐positions. It was found that simple alkyl substitution leads to prismanes only to a minor extent. Introduction of phenyl groups into the 2‐ or 2,3‐positions gives the corresponding doubly bridged prismanes in yields up to 80% Pentamethylene‐bridged bis‐Dewar benzenes 19 rearrange upon irradiation to 22. Irradiation of the doubly bridged Dewar benzene derivatives with one ester group at the 5‐position does not yield isolable products. However, introduction of one tert‐butylsulfonyl group such as 30–33 gives almost quantitative yields of isolable prismanes if pentamethylene or hexamethylene bridges are used. The nonbridged species, 2‐tert‐butylsulfonyl‐1,4,5,6‐tetramethylbicyclo[2.2.0]hexa‐2,5‐diene (44), aromatizes upon irradiation into 1‐(tert‐butylsulfonyl)‐2,3,4,5‐tetramethylbenzene (45). In contrast to the pentamethylene‐bridged monosulfone 47, the corresponding disulfone 38 undergoes no photochemical reaction. This could be explained by the X‐ray structure, which reveals a strong interaction between one of the tert‐butyl groups and the pentamethylene chain bridging the double bond in 38.
Conformations and Rotational Barriers of (Z)‐1,2‐α‐Naphthostilbene Crown Ethers and Their Alkali Metal Complexes
Authors: Merz Andreas , Gromann Lutz , Karl Andreas , Burgemeister T. , Kastner F.
Published: July 2007

The synthesis of 2,3‐didehydro[15]crown‐5 and −[18]crown‐6 derivatives 4a, b with vicinal α‐naphthyl groups at the double bonds starting from α‐naphthoin (3) is described. The barriers to rotation of the naphthyl groups were probed by MM2 and by dynamic 1H‐NMR spectroscopy. An achiral syn and a chiral anti conformation were experimentally observed at −90°C for the free ligands and at −40°C for the complexes. The experimental ΔG≠ and the calculated ΔH≠ values are in fair agreement. The barriers are substantially higher in the alkali metal complexes than in the free ligands. In the presence of racemic and potassium S‐(+)‐mandelate non‐equilibrating ion pairs with 4b were observed by low‐temperature 1H‐NMR spectroscopy for the anti conformation.
A Conformational Study of [3.3](2,6)Pyridinophane by the Dynamic NMR Method and X‐ray Structural Analysis
Authors: Sako Katsuya , Tatemitsu Hitoshi , Onaka Satoru , Takemura Hiroyuki , Osada Satoshi , Wen Gang , Shinmyozu Teruo , Rudziński Jerzy M.
Published: July 2007

A variable‐temperature 1H‐NMR study and X‐ray structural analysis show that the most stable conformational isomer of [3.3](2,6)pyridinophane 2 is the syn(boat‐boat) conformer, and the relative stability order of the three stable conformers is syn(boat‐boat) > syn(chair‐boat) > syn(chair‐chair). This is in sharp contrast to the relative stability order of the parent [3.3]metacyclophane 1: syn(chair‐chair) > syn(chair‐boat) > syn(boat‐boat). The high stability of the syn(boat‐boat) conformer 2c is primarily attributed to weak attractive interactions via intramolecular hydrogen bonds between nitrogen lone pairs (N‐1, N‐2) and the axial hydrogen atoms (2A‐H, 11A‐H) on the central carbon atoms of the bridges, as suggested by their short transannular distances (2.50 Å).
Synthesis of 4′,7‐Dihydroxy‐6‐methoxyisoflavone 7‐O‐β‐d‐Glucopyranoside (Glycitin)
Authors: Nógŕdi Mihály , Szöllosy Áron
Published: July 2007

The aglycone glycitein (1) of the title glucoside glycitin (2) was prepared by oxidative rearrangement of the fully protected chalcone 4 by Tl(NO3)3 in MeOH into 5 followed by deprotection and ring closure. Its glucosylation with α‐acetobromoglucose and subsequent saponification gave 2 as the main product.
2‐Chloro‐4,5‐dihydroimidazole, 8. Syntheses of Novel Fused Heterocyclic Systems by Reactions of 1,2‐Dihydro‐2‐(4,5‐dihydroimidazol‐2‐yl)phthalazin‐1‐ol with Active Methylene Compounds
Authors: Saczewski Franciszek , Gdaniec Maria
Published: July 2007

Three‐component reactions of 1 with pyridazine or phthalazine afforded the 1,2‐dihydro derivatives 2a and 2b, respectively. A similar reaction of 1 with phthalazine performed in aqueous NaOH led to the formation of pseudobase 3. The latter compound proved to be an excellent substrate for the preparation of a series of novel 1,2‐dihydrophthalazine derivatives 4a–c, 5 as well as 6a–b by reactions with a variety of active methylene compounds.
A New Assay For Sialyltransferases Using Fluorescein‐Labelled Acceptors
Authors: Limberg Gerrit , Slim George C. , Furneaux Richard H. , Compston Catharine A. , Stangier Peter , Palcic Monica M.
Published: July 2007

A novel HPLC assay system for sialyltransferase activity based on the use of fluorescein‐labelled acceptor oligosaccharides is described. The fluorescein‐labelled disaccharides βGal‐(1→4)‐βGlc‐OR (4), βGal‐(1→4)‐βGlcNAc‐OR (17), and βGal‐(1→3)‐βGlcNAc‐OR (22) where OR consists of a six carbon spacer with fluorescein attached, were synthesised. Synthetic standard products were produced chemo‐enzymatically on a preparative scale to yield fluorescein‐labelled trisaccharides. The use of reverse phase HPLC with an ionpairing agent allowed the separation of starting materials from products and separation of the two isomeric trisaccharides αNeu5Ac‐(2→3/6)‐βGal‐(1→4)‐βGlcNAc‐OR (24 and 25), so that the assay could be used to measure the different silalyltransferase activities in a mixture. The assay was successfully applied to the detection of sialyltransferase activity of commercially available enzymes and a crude preparation of bovine colostrum. The predominant sialyltransferase activity in bovine colostrum adds sialic acid α(2–6) to 17.
Synthesis of Protected Enantiopure Erythrulose Derivatives
Authors: Alberto Marco J. , Carda Miguel , González Florenci , Rodríguez Santiago , Murga Juan
Published: July 2007

D‐ and l‐Erythrulose derivatives 2–6 bearing protective O‐silyl and O‐benzyl groups in various positions were synthesized in enantiopure form from l‐ascorbic acid, D‐isoascorbic acid, and D‐glucose.
Pheromone Synthesis, CLXXVI. Synthesis of the Four Stereoisomers of 3,13‐Dimethylheptadecane, the Major Sex Pheromone Component of the Western False Hemlock Looper
Authors: Takikawa Hirosato , Shirai Yasuo , Kobayashi Makoto , Mori Kenji
Published: July 2007

All of the four stereoisomers of 3,13‐dimethylheptadecane (1), the female‐produced sex pheromone of the western false hemlock looper (Nepytia freemani), were synthesized by starting from the enatiomers of citronellol (2a) and 2‐methyl‐1‐butanol (4a).
Photochemistry of [2.2]Paracyclophan‐enes — a Matrix‐Isolation Study
Authors: Marquardt Ralph , Sander Wolfram , Laue Thomas , Hopf Henning
Published: July 2007

The UV photolysis of [2.2]paracyclophan‐ene (3) and benzo‐[2.2]paracyclophan‐ene (4), matrix‐isolated in argon at 10 K, results in the cleavage of the ethano bridge and formation of compounds5and8, respectively. The IR and UV/Vis spectra are compared withp‐xylylene and the benzyl radical as models for a quinoid or diradicaloid structure. The absence of an ESR signal reveals a singlet ground state for these compounds. Remarkable is a sharp absorption in the red part of the visible spectrum which is not observed in the case ofp‐xylylene or the benzyl radical. The electronic structure can be described as quinoid with a substantial amount of diradicaloid character.
Nitroalkanes as Alkyl Anion Synthons — A New Approach to the Synthesis of 2‐Substituted N‐Ethyl Succinimides and 2‐Substituted Succinate Diesters via Nitroalkanes
Authors: Ballini Roberto , Bosica Giovanna
Published: July 2007

2‐Substituted N‐ethyl succinimide and 2‐substituted succinate diesters were obtained by two key steps: (i) Michael addition of a nitroalkane to the appropriate enedione derivative under basic conditions (DBU), with the concomitant elimination of nitrous acid, and (ii) selective reduction of the obtained enone with nickel boride, in methanol/THF. In this context the nirtoalkane acts as an alkyl anion synthon. By this method trimethyl tricarboxylates were also synthesized.
Monolayer and Bilayer Stability of Ammonium Amphiphiles Carrying an Azobenzene Unit – Effects of Substituents at the Azobenzene Unit
Authors: Everaars Marcel D. , Marcelis Antonius T. M. , Sudhölter Ernst J. R.
Published: July 2007

Novel double‐chained ammonium amphiphiles carrying one azobenzene moiety (I) have been synthesized. The bilayer‐stabilizing effect of different azobenzenes (ABs) has been investigated by measuring the “gel‐to‐liquid crystalline” phase transition temperatures of the formed bilayers in water using differential scanning calorimetry. It is found that the stabilizing effect of the azobenzenes strongly depends on the substituents at the aromatic ring. The stabilizing effect increases in the sequence F < H < NO2 < CN < OCH3 < N=N–Ph, which cannot be correlated with the electron‐withdrawing or ‐donating properties of the substituents. It is concluded that dipole‐dipole interactions between the ABs are of minor importance for the overall stabilization of the bilayer. Instead, other factors determine the strength of the van der Waals interactions between the ABs. In the bilayers the ABs form H‐aggregates as is observed by the blue shift of the UV absorption maximum. This blue shift is not affected by the “gel‐to‐liquid crystalline” phase transition. Bilayers of I–N=N–Ph do not exchange monomers with vesicles of didodecyldimethylammonium bromide, whereas all other investigated bilayers do. Compound I–N=N–Ph forms monolayers at the water‐air interface, which are much more stable than the monolayers of the other investigated compounds.
Quantification of the Electrophilicities of Diazonium Ions
Authors: Mayr Herbert , Hartnagel Manfred , Grimm Klaus
Published: July 2007

The kinetics of the reactions of arenediazonium ions with arenes, alkenes, allylsilanes, allylstannanes, and silyl ketene acetals have been studied in acetonitrile solution. The reactions follow second‐order kinetics, and in several cases rate‐determining attack of the diazonium ion has been proven by kinetic isotope effect studies (1a + 2b), by the independence of the allylsilane reactivities of the rate of desilylation (1a + 10a, d) and by the independence of the rate constants of the diazonium counterion. A decrease of the rate constant with increasing solvent donor ability (correlation with Gutmann's donor number) was found. The reactions of diazonium ions with π‐nucleophiles roughly follow the correlation lgk (20°C) = s (E + N), previously derived for the reactions of carbocations with nucleophiles. With the E parameters derived for diazonium ions, rate constants for azo couplings with aromatic and nonaromatic π‐nucleophiles can be predicted with an accuracy of ≈102. On the basis of E, the electrophilic reactivities of diazonium ions can be compared with those of carbocations (Figure 9), and the combination with the nucleophilicity parameters N (Figure 10) gives a first clue on possible azo coupling reactions. Literature reports are discussed within this scheme.
From p‐Dimethoxybenzene to Crown‐benzenophanes, 4– Cation‐Complexing Properties of Bis(p‐phenylene‐34‐crown‐10) – A Structural and Spectrophotometric Study
Authors: Marquis Damien , Greiving Helmut , Desvergne Jean‐Pierre , Lahrahar Nacer , Marsau Pierre , Hopf Henning , Bouas‐Laurent Henri
Published: July 2007

The title compound 2, an electron‐rich macrocyclic paracyclophane of the coronand type, known to form a charge‐transfer complex with paraquat, was found to encapsulate strontium cations and to bind to magnesium cations. X‐ray analysis revealed that 2 forms a 2:1 (metal/substrate) complex with Sr(ClO4)2, in which the two benzene rings weakly overlap, whereas in the single crystals grown from Mg(ClO4)2, the metal cation prefers to lie outside the coronand (1:1 stoichiometry). In acetonitrile solution, cations were observed to trigger an hypsochromic shift of the UV absorption spectra, proportional to their size and charge density. The stoichiometries and binding constants were also determined by UV absorption titration in acetonitrile using the LETAGROP‐SPEFO program for several monovalent and divalent cations. For Na+, Ca2+, and Sr2+, 1:1 and 2:1 complexes were shown to be formed. In the free ligand, a weak interaction between the benzene rings was detected by fluorescence decay kinetic analysis, indicating the presence of two conformer populations within the nanosecond time scale. In solution, metal cations neither induce detectable excimer formation nor seem to have a strong influence on the fluorescence emission spectra, except a heavy atom quenching with Sr2+ and Ba2+, in contrast to the effect observed in absorption. However, Sr2+ and Mg2+induce a clear hypsochromic shift in the single crystal fluorescence spectra. Compound 2 was prepared by a new and efficient route which is compared to the previous procedures.
Synthetic Applications of Bis(iminophosphoranes) – Preparation of Some Derivatives of the 11H‐Quinazolino[2,3‐b]‐ and Quinazolino[4,3‐b]quinazoline Ring Systems
Authors: Molina Pedro , Conesa Carlota , de los Desamparados Velasco M.
Published: July 2007

Aza Wittig reaction of bis(iminophosphorane) 3 with two equivalents of aryl isocyanates directly provided the bicyclic guanidines 4. However, 3 undergoes intramolecular aza Wittig reaction on thermal treatment to give the iminophosphorane 6 derived from the 2‐(o‐azidophenyl)‐4(3H)‐quinazolinone. Compound 6 reacts with isocyanates, acyl chlorides and carbon disulfide to yield quinazolino[4,3‐b]quinazoline derivatives 8a–c, 9a–c, 10, and 11.
Secondary Fungal Metabolites and Their Biological Activity, VIII. – Partial Synthesis of Oosponol, an Antifungal Isocoumarin
Authors: Kovács Tibor , Sonnenbichler Johann
Published: July 2007

The partial synthesis of oosponol (4), which shows significant antibiotic activity, has been accomplished by enzyme catalyzed reactions including regioselective acetylation of (−)‐oospoglycol (1) followed by an oxidation step and hydrolysis by a lipase.
Solvolysis of Tricyclo[4.1.0.02,7]hept‐4‐en‐3‐yl and Tricyclo[4.1.0.02,7]hept‐3‐yl Methanesulfonates and p‐Nitrobenzoates – Remarkably Small Enthalpy Difference between the C7H7 Cations Tricyclo[4.1.0.02,7]hept‐4‐en‐3‐yl and 7‐Norbornadienyl
Authors: Bentley T. William , Llewellyn Gareth , Norman Simon J. , Kemmer Ralf , Kunz Ulrike , Christl Manfred
Published: July 2007

In an extension of previous work, tricyclo[4.1.0.02,7]heptan‐3‐ol (5) was synthesised in four steps from benzvalene. Methanesulfonates 12 and 6b, c, prepared from 5 and 4‐halotricyclo[4.1.0.02,7]hept‐4‐en‐3‐ols 4b, c, were too unstable to be isolated, but were unambiguously characterised by their NMR spectra. On treatment of the unsubstituted tricycloheptenol 4a with methanesulfonyl chloride, the expected mesylate 6a could not be observed. Even at −40°C, only its consecutive products 3‐chlorotricyclo[4.1.0.02,7]hept‐4‐en (7a) and 7‐chloronorbornadiene (8a) were discernible. The analogous reaction of 6b occurred only at room temperature, with formation of the dichlorotricycloheptene 7b and the dichloronorbornadiene 8b. Rearrangement products of 6b and 12 were the chloronorbornadiene mesylate 10b and anti‐7‐norbornenyl mesylate (13), respectively. – The solvolysis of 6b, c in aqueous ethanol and of 6b in 2,2,2‐trifluoroethanol (TFE) gave nonrearranged products exclusively, i.e. the alcohols 4b, c, the ethyl ethers 17b, c, and the trifluoroethyl ether 18b. In contrast, from 12 only rearranged products arose, namely anti‐7‐norbornenol (30) and its ethyl ether 31. The solvolysis of the unsubstituted tricycloheptenyl p‐nitrobenzoate 11a in 80% aqueous ethanol proceeded about equally fast in parallel reactions with cycloalkyl‐oxygen and acyl‐oxygen cleavage. In addition to the tricycloheptenol 4a, the tricycloheptenyl ethyl ether 17a, ethyl 7‐norbornadienyl ether (19), 7‐norbornadienyl p‐nitrobenzoate (20), and ethyl p‐nitrobenzoate were formed. No acyl‐oxygen cleavage took place in TFE as solvent, where the tricycloheptenyl trifluoroethyl ether 18a, 20, 7‐norbornadienyl trifluoroethyl ether (21), and the cyclopentadienylvinyl trifluoroethyl ethers 22/23 were produced. A new mechanism is proposed for the route to the major products 22/23 via the intermediate 7‐norbornadienyl cation (9a), which was attacked by TFE at the two‐membered bridge stabilising the positive charge. Thus formed, tricyclo‐[3.2.0.02,7]hept‐3‐en‐endo‐6‐yl trifluoroethyl ether (24) underwent a Diels‐Alder cycloreversion generating the cyclopentadienylvinyl trifluoroethyl ether 25, the immediate precursor of 22/23. – From kinetic data for these processes and thermochemical data for appropriate hydrocarbons, the enthalpy difference between the C7H7 cations, tricyclo‐[4.1.0.02,7]hept‐4‐en‐3‐yl (3a) and 7‐norbornadienyl (9a), was calculated to be only 8 kcal mol−1.