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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of Medium- and Large-Ring Compounds Initiated by Photochemical Decarboxylation of ω-PhthalimidoalkanoatesDedicated to Prof. Waldemar Adam and Prof. Dieter Seebach on the occasions of their 60th birthdays on July 26th and October 31st 1997, respectively (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 912-933 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a variety of hydroxylactams from ω-phthalimidoalkanoates using a triplet-sensitized photodecarboxylation reaction initiated by intramolecular photo electron transfer is described. Ring sizes available by this method span from 4 (benzazepine-1,5-dione 7) to 26 (cyclodipeptide 26e). Ground-state template formation is proposed as the explanation for the high efficiency of this reaction and for the decrease in reactivity in the presence of organic bases instead of metal carbonates. The crucial step in this macrocyclization reaction seems to be the protonation of the intermediary ketyl radials (Scheme 4). Spacer groups investigated were alkyl chains (C3-C11: 5c-h, 11a, 12), ether (16, 18), ester (20, 22), and amide (26a-f) linkages. Within the detection limits, no dimeric (= decarboxylative coupling) products were observed, indicating the high preference for intra-vs. intermolecular photoelectron transfer. The C,C radical combination step proceeds with low stereoselectivity (cf, products 11 and 12) in contrast to comparable singlet reactions. Except for the lactones 22, all products were stable under the photolysis conditions. Prolonged irradiation of 22 led to the formation of the spiro compounds 23, probably via an intermediary acyliminium betaine (Scheme 8). One serious limitation of the decarboxylative macrocyclization is its incompatibility with the glycine spacer (as in 27a and 27b), probably the consequence of a strong intramolecular H-bond (Scheme 10).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800324
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  • 2
    Electronic Resource
    Electronic Resource
    Synthese mittlerer und großer Ringe, XXXI[1] Die [6](3,6)Oxepinophan-[6](2,5)Furanophan-Ringverengung mit Rutheniumtetroxid (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 1485-1494 
    Details
    ISSN: 0009-2940
    Keywords: Oxepines ; Furans ; Ruthenium tetroxide ; Iron complexes ; Heterophanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Medium and Large Rings, XXXI[1] - The [6](3,6)Oxepinophane-[6](2,5)Furanophane Ring Contraction with Ruthenium TetroxideA one-pot synthesis of the furanophanes 2a and 2b by ring contraction of the oxepinophanes 1a and 1b is described. Evidence is presented that the reaction proceeds by subsequent oxidation of two double bonds via the intermediates 3 and 4. On treatment with hydrochloric acid cis-4 gives 2a by 1,4-elimination of hydrogen peroxide. The oxidation of the [7](3,6)oxepinophane 1c leads to a complex mixture of the products 2d and 6-10. 2a undergoes Diels-Alder reactions with benzyne and 2,3-naphthalyne to give 11 and 12. The latter forms the stable iron tricarbonyl complex 13. The structures of 2c, 4, 10, 11, and 13 have been established by X-ray analyses.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250626
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of α-amino-3-chloro-4,5-dihydro-5-methyl-5-isoxazoleacetic acid, a ring-methylated analogue of the antitumor agent acivicin (AT-125) (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 619-623 
    Details
    ISSN: 0947-3440
    Keywords: Acivicin ; Photochemistry ; 1,3-Dipolar cycloadditions ; Nitrile oxides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α-Amino-3-chloro-4,5-dihydro-5-methyl-5-isoxazoleacetic acid (8), a ring-methylated analogue of the potent antitumor agent acivicin (AT-125), is synthesized in a 6-step procedure in 63% overall yield from (S)-valine. Key step is the 1,3-dipolar addition of bromonitrile oxide to the N,C-protected (S)-isodehydrovaline (6) available from (S)-valine in four steps involving the photoisomerization of N-phthaloylvaline methyl ester (1). The stereochemical course of the 1,3-dipolar cycloaddition is proven by means of a X-ray structure analysis of the major diastereoisomer 7a formed in the chloronitrile oxide cycloaddition. The absolute configuration of the major (u) diastereomer 7a and the bromo derivative 7b is (αS,5R).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950486
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  • 4
    Electronic Resource
    Electronic Resource
    Ring Expansion of Heterocyclic Ketene N,X-Acetals and 2-Alkylidenedihydroindoles with Methanesulphonyl Azide by [3 + 2] Cycloaddition and Subsequent Extrusion of Molecular Nitrogen (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1541-1549 
    Details
    ISSN: 0947-3440
    Keywords: [3 + 2] Cycloaddition ; Ketene N,X-acetals, cyclic ; Azides, electrophilic ; Amidines, cyclic N-sulphonyl- ; Ring expansion of heterocycles ; 1,2-Shift of carbon, nitrogen, sulphur, or selenium ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methanesulphonyl azide (2) reacts readily with isolated cyclic ketene N,X-acetals of type 1, viz. 10a, d, 15b, d, and 22a-c, or those that are generated in situ by deprotonation of the corresponding 2-alkylbenzazolium tetrafluoroborates, i.e. 14a → 15a, 14b → 15b, and 18 → 19. Ring-expanded products are formed by extrusion of molecular nitrogen from intermediate labile [3 + 2] cycloadducts 3 with concomitant 1,2-shift of N (route A1 → 12, 24) or X (route A2 → 16, 20, 21). In addition, 3 may undergo [3 + 2] cycloreversion into N-sulphonylimine 5 and diazoalkane 6 (route B → 13, 17, 25). The configurations of the cyclic N-sulphonylamidines 16b and 21b, the N-sulphonylimine 24 and the N-sulphonylamine 27 are elucidated by means of X-ray diffraction analyses. The ratio of the (useful) ring-expansion reactions vs. the unwanted formation of 5 + 6 is hardly influenced by the solvent employed and temperature of the experiment but strongly by the nature of the potential migrating atom and the substituents at the α-carbon atom.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961008
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  • 5
    Electronic Resource
    Electronic Resource
    Zwitterions as Intermediates in 1,3-Dipolar Cycloadditions of Electrophilic Azides to 2-Alkylidenetetrahydroimidazoles and 2-AlkylidenedihydrobenzimidazolesDedicated to Professor Günter Szeimies on the occasion of his 60th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1551-1558 
    Details
    ISSN: 0947-3440
    Keywords: Ketene N,N-acetals, cyclic ; Imidazole, derivatives of ; Benzimidazole, derivatives of ; Azides, electrophilic ; Cycloaddition, 1,3-dipolar, nonconcerted ; Zwitterions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961009
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  • 6
    Electronic Resource
    Electronic Resource
    An Attempted Synthesis of 2,6-Bis(phenylazo)barbaralane (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1733-1738 
    Details
    ISSN: 0947-3440
    Keywords: Azo compounds ; Cyclizations ; Hydrazones ; Michael additions ; Nitrogen heterocycles ; Oxidations ; Polycycles ; Rearrangements ; Strained molecules ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of the unsaturated ketone 6 with phenylhydrazine fails to afford the unsaturated phenylhydrazone 3 but gives the tricyclic phenylhydrazoketone exo-8, which is oxidised with iron(III) chloride to yield the phenylazoketone exo-9. The configuration of exo-9 is elucidated with the help of an X-ray diffraction analysis. The unsaturated phenylazo compound 14 is obtained from Meerwein's diketone 10 in two ways. Iodination of the phenylhydrazone 11 in the presence of pyridine followed by elimination of pyridinium iodide from the bispyridinium salt 13 with aqueous sodium hydroxide in dimethyl sulphoxide furnishes 14 in low yield. A somewhat better yield is more conveniently achieved when the dibromodiketones exo,exo- and exo,endo-12 are allowed to react with phenylhydrazine in the presence of pyridine. Bromination of 14 with N-bromosuccinimide in cyclohexane as solvent affords the labile dibromide 15. Both reagents employed, viz. the zinc/copper couple in refluxing tetrahydrofuran and butyllithium at low temperature, fail to convert 15 into the hoped-for bis(phenylazo)barbaralane 1 but instead give rise to the formation of the isomer 17, either by cyclisation of the intermediate anion 16 or by rearrangement of 1.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970815
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  • 7
    Electronic Resource
    Electronic Resource
    A Novel Synthesis and the Autoxidation of 2,4,6,8-TetraphenylbarbaralaneDedicated to Professor Waldemar Adam on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 685-698 
    Details
    ISSN: 0947-3440
    Keywords: Autoxidation ; Copolymerisations ; Cyclizations ; Diradicals ; Epoxidations ; Liquid Chromatography ; Oxygen ; Peroxides ; Polycycles ; Radical Reactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Addition to the diphenyldiketone 11 of the reagent prepared from rigorously dried cerium(III) chloride and phenyllithium yields the tetraphenyldiol endo,endo-13 after extended periods of time. The configuration of this diol, which was previously assigned the (incorrect) configuration exo,exo-13, is established by an X-ray diffraction analysis. Dehydration of endo,endo-13 with sulphuric acid in acetic acid affords a mixture of the oxatwistane 16 and the tetraphenyldiene 17 (3:1). Only the latter is obtained from endo,endo-13 by the action of boron trifluoride-diethyl ether in dichloromethane solution. While attempts at allylic bromination of 17 with N-bromosuccinimide in conventional solvents inevitably lead to complete decomposition, use of cyclohexane as solvent allows to obtain solutions of allylic dibromides that can be cyclised with the zinc-copper couple to afford tetraphenylbarbaralane 9 in 58% yield based on 17. Thus, 9 is now available from the diphenyldiketone 11 in only three steps with an overall yield of 42%. - The autoxidation of 9, studied in various solvents, yields mixtures of products of which the epoxyendoperoxides 20 and 21, the unsaturated ketone 22, and a labile, probably oligomeric or polymeric product C are isolated in pure form. The structures 21 and 22 are elucidated by X-ray diffraction analysis and independent synthesis, respectively. On warming, 20 rearranges into 21. Traces of acid convert the unknown autoxidation product A instantaneously into the unsaturated ketone 22. - Rate studies show that the autoxidation of 9 starts after a short initiation period. 2,6-Di-tert-butyl-4-methylphenol exhibits powerful inhibitory effects. These results demonstrate the free radical nature of the autoxidation of 9. - The results are interpreted in terms of a mechanistic scheme involving initiation of the radical chain by addition of triplet oxygen to 9 to generate the diradical 28 followed by a radical chain 1:1 copolymerisation of 9 and oxygen to produce diradical 29. Eventually, endo addition of oxygen to 29 gives rise to the formation of the epoxyendoperoxides 20 and 21. Intramolecular hydrogen abstraction from the methylene group (C9) is accompanied by cleavage of a bridgehead bond (C1-C2) and the adjacent O-O bond to afford the extremely labile product A (perhaps 32 or 33) which undergoes acid-catalysed elimination to furnish ketone 22.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970409
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of Medium and Large Rings, XLIVPart XLIII: W. Tochtermann, L. Rodefeld, H. Dreeskamp, S. M. Sage, Liebigs Ann. 1996, 1959-1961.. Synthesis of Optically Active Bridged Bicyclobutane DerivativesDedicated to Professor Hans Paulsen on the occasion of his 75th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1125-1129 
    Details
    ISSN: 0947-3440
    Keywords: Oxepines ; Photoisomerization ; s-cis-Butadiene conformation ; Small ring systems ; Enantiomeric resolution ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of the dihydrooxepine monoester (+)-4 gives the bridged bicyclobutane (+)-5 in 77% yield. On the other hand, the corresponding diester 1 yields the cyclobutene 2. Possible explanations for this differing behaviour are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970611
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  • 9
    Electronic Resource
    Electronic Resource
    Optimised preparation of 1,5-dialkylsemibullvalenesDedicated to Professor Paul von Ragué Schleyer on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1159-1168 
    Details
    ISSN: 0947-3440
    Keywords: Semibullvalenes ; Tricyclo[3.3.0.02,8]octa-3,7-dienes ; Barbaralane ; [3.3.3]Propellanes ; [4.3.3]Propellanes ; Bicyclo[3.3.0]octadienes, dibromo-, configuration of ; Allylic bromination ; Reductive cyclisation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Askani's synthesis of the 1,5-dialkylsemibullvalenes 1a and c was optimised on a gram scale. The as yet unknown trimethylenesemibullvalene 1b was obtained according to the same protocol which also greatly improved a recent synthesis of barbaralane (2). Allylic brominations of the dienes 5 + 6 with N-bromosuccinimide yielded complex mixtures of 7-10. Depending on the substitution pattern at the apical carbon atoms C-1 and C-5 of the bicyclo[3.3.0]octadiene system, the intermediate allylic radicals are attacked preferentially either from the exo (R = Me) or from the endo face [R, R = (CH2)3, (CH2)4]. Reductive cyclisations of the dibromides 9 and exo,exo-15 were carried out with a sonicated suspension of an activated zinc-copper couple in tetraglyme. Sweeping of the volatile products from the reaction mixtures with nitrogen at elevated temperatures allowed the convenient isolation of the semibullvalenes 1 and barbaralane (2) in reasonable purities (92-97%) and yields (57-82%).
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507157
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  • 10
    Electronic Resource
    Electronic Resource
    Cycloallenes, 11.Part 10: Ref. [1] 1-Phenyl-1,2-cyclononadiene: Preparation and Dimerisation (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1791-1796 
    Details
    ISSN: 0947-3440
    Keywords: Allenes ; Carbenoids ; Cycloadditions ; Dimerisations ; Rearrangements ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1-Phenyl-1,2-cyclononadiene (10) was prepared by addition of dibromocarbene to 1-phenylcyclooctene and treatment of the resulting 9,9-dibromobicyclo[6.1.0]nonane 7 with methyllithium. In addition to 10, the 9-bromo-9-methylbicyclononanes cis- and trans-8 as well as the bicyclopropylidene 9 were formed. The dimerisation of 10 proceeded slowly already at room temperature and gave rise to the 1,2-bismethylenecyclobutane derivatives cis- and trans-11. From the complex mixture that resulted on thermolysis at 200°C of cis- and trans-11 only their isomer 12 could be isolated. Heating of a benzene solution of tetracyanoethylene and cis- and trans-11 afforded the Diels-Alder adduct 13 of cis-11, which rearranged to the benzodicyclononene derivative 14 on thermolysis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970825
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