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  • 1
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die bevorzugte Durchführung organischer Synthesen bei möglichst tiefen Temperaturen beruht auf der an vielen Beispielen bestätigten und auch theoretisch begründeten Annahme, daß die Selektivität häufig mit sinkender Temperatur zunimmt. Mangelnde Selektivität ist nicht das einzige Problem von Hochtemperaturreaktionen, hinzu kommt unter anderem die oft begrenzte thermische Stabilität der an der Umwandlung nicht direkt beteiligten funktionellen Gruppen und Strukturelemente. Trotz dieser Einschränkungen lassen sich die Vorteile hoher Temperaturen, vor allem dank der in den letzten Jahren stark erweiterten Kenntnisse der Mechanismen dynamischer Gasphasenprozesse, für die gezielte organische Synthese nützen. In diesem Fortschrittsbericht wird das Synthesepotential der „Gasphasen-Strömungsthermolyse“ aus der Sicht des präparativ arbeitenden Chemikers anhand typischer Anwendungsbeispiele beschrieben.
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  • 3
    ISSN: 0570-0833
    Keywords: Gas-phase flow thermolysis ; Thermolysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preference for carrying out synthetic organic reactions at the lowest possible temperature is due to the expectation that the selectivity often increases with decreasing temperature, as is confirmed by many examples and also theoretically justified. Selectivity, however, is not the only problem at high temperatures; further factors include the frequently limited thermal stability of the functional groups and structural elements not directly involved in the transformation. In spite of these limitations, the advantages of high temperatures and the greatly improved knowledge of the mechanisms of dynamic gas-phase processes accumulated in recent years can be exploited in directed organic synthesis. In this review the synthetic potential of gas-phase flow thermolysis will be described from the viewpoint of the synthetic chemist with the aid of typical examples of application.
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Synthesis of Bicyclo[10.3.0]pentadec-1(12)-en-13-one and its 14-Methyl Derivative.A new route to bicyclo[10.3.0]pentadec-1(12)-en-13-one (2) and its 14-methyl derivative 3 - useful intermediates in the synthesis of cyclopentadecanone (4 = exaltone®) and rac-muscone (5) - is described.
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  • 5
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azimines. IITeil I, siehe [1]. . Preparation and Thermal Fragmentation of cis- and trans-2,3-Diphenyl-1-phthalimido-2,3-di[15N]-azimine Teilweise vorgetragen in der Versammlung der Schweizerischen Chemischen Gesellschaft am 8./9. Oktober 1976 in Genf und als Autoreferat veröffentlicht [2].cis- and trans-2,3-Diphenyl-1-phthalimido-2,3-di[15N]-azimine (11 and 12) wer synthesized from cis-di[15N]-azobenzene (10) and phthalimido-nitrene (2), the latter generated by lead tetraacetate oxidation of N-aminophthalimide (1). Useful information was obtained from the comparison of several data of 11 and 12 with those of the unmarked diphenyl-azimines 5 and 6 (R = C6H5).The 15N- and 13C-NMR. spectra of 11 and 12 were interpreted to furnish additional evidence for the azimine structure and for the indicated configurations. The IR. spectra permitted identification of two bands in the 1200 to 1450 cm-1 region, probably characteristic for the functionality of diaryl-phthalimido-azimines. Comparison of the mass spectrum of 11/12 with that of the unmarked analogues 5/6 (R = C6H5) permitted the interpretation of the fragmentation path of 1-phthalimidoazimines. The major path may be the purely thermal decomposition to 13 and 7 (R = C6H5), respectively. Two other competing fragmentation paths are discussed.Prolonged thermolysis of 11 at 61° in solution gave 83% of N,N′-diphenyl-N N′-phthaloyl-di[15N]-hydrazine (13) of 98% isotope purity, which means that the imide nitrogen atom and N(1) of the azimine function are removed in this reaction. A mechanism passing through an intermediate cyclic tetrazene 16 is considered.Benzocyclobutenedione (14) added to trans-azobenzene (4, R = C6H5) under the influence of a high pressure lamp in a quarz apparatus to give N,N′-diphenyl-N,N′-phthaloyl-hydrazine (7, R = C6H5). This reaction was found not to take place in the dark, even after prolonged heating in trichloromethane.
    Additional Material: 2 Tab.
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  • 6
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azimines. I. Synthesis and Stereoisomerism of 2, 3-Diaryl- and 2, 3-Dialkyl-1-phthalimido-aziminesTeilweise vorgetragen in der Versammlung der Schweizerischen Chemischen Gesellschaft in Lausanne am 7./8. Mai 1971 und als Autoreferat veröffentlicht [1].Special examples of a new class of compounds, the open-chain azimines (1), have been prepared and their properties examined.Addition of phthalimido-nitrene (4), generated by lead tetraacetate oxidation of N-aminophthalimide (3), to cis- and trans-azobenzene (6 and 5), -azo-p-toluene (8 and 7), and to trans-azomethane (9), -azoethane (10) and -azo-α-phenylethane (11) afforded the separable cis- and trans-isomers of 2, 3-diphenyl- (12 and 13), 2, 3-di-p-toyl- (14 and 15), 2, 3-dimethyl- (16 and 17), 2, 3-diethyl- (18 and 19) and 2, 3-di-(α-phenylethyl)-1-phthalimido-azimines (20 and 21) in different ratios (see Scheme 1).The constitution of the nitrene azo compound adducts as azimines was derived from their properties, especially from the conjugation effect (visible in the UV. spectra) of the aryl-substituted compounds and from the non-equivalence (shown by the 1H-NMR. spectra) of the substituents on the two nitrogen atoms derived from the azo compounds. This evidence excluded the triaziridine 22 and an alternative azimine constitution 23 for the adducts.Of the two stereoisomers obtained for each of the azimines, the aryl-substituted examples 12/13 and 14/15 were readily interconverted by warming in solution, the cis-isomers 12 and 14 exceeding the trans-isomers 13 and 15 in the equilibrium. The dialkyl-azimines appear to be configurationally more stable, since interconversion of the dimethyl-azimines 16 and 17 was not possible under the same conditions, and also not before another thermal reaction took place (see below).The identification of the N(2)-N(3) bond as the stereogenic center, i.e. that the stereoisomerism of the azimines is due to the difference in relative position at N(2) and N(3) of the substituents derived from the azo compounds, as well as a configurational assignment was possible in the aryl-substituted examples on the basis of the UV. spectroscopic comparison of the isomeric azimines with the corresponding stereoisomeric azoxy compounds: The cis-azimines 12 and 14 showed absorptions similar to those of cis-azoxybenzene and cis-azoxy-p-toluene, and the trans-azimines 13 and 15 showed absorptions similar to those of the respective trans-azoxy compounds. With respect to the configuration of the alkyl-substituted azimines, it was observed that the isomers 17 and 19, which from their formation and chromatographic behaviour are likely to be the trans-isomers, show a visible coupling (∽ 1 Hz) between the two H (α)'s in the 1H-NMR. spectrum, whereas the dimethyl isomer 16 (cis) does not exhibit such a coupling.Thermal treatment of four azimines, namely 12, 14, 16 and 17, in solution for a longer time afforded the corresponding N, N′-disubstituted N, N′-phthaloyl-hydrazines 27, 28 and 29. The order of velocity of this fragmentation with nitrogen extrusion was 12/13 ≍ 14/15 〉 16(cis) 〉 17(trans).
    Additional Material: 1 Ill.
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  • 7
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
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  • 8
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Mechanism of the α-Alkynone Cyclization: Synthesis and Thermolysis of 1-(1-Methylcyclopentyl)[3-13C]prop-2-ynoneThe relative migratory aptitude of two acetylenic substituents in the α-alkynone cyclization, a thermal conversion of α-acetylenic ketones A to 2-cyclopentenones C, was investigated by isotope-labeling experiments. The α-alkynone [β-13C]-1, specifically labeled with 13C at the β-acetylenic C-atom C(3), was synthesized by an intramolecular Witting reaction (230-300°) of the diacylmethylidenephosphorane [13C]-7. The latter resulted from acylation of methylidenetriphenylphosphorane with the acid chloride 4 to yield the acylmethylidenephosphorane 5, which in turn was formylated with acetic [13C]formic anhydride ([13C]-6.) Upon thermolysis of [β-13C]-1, its label at C(β) was transferred almost exclusively to C(β) of the 2-cyclopentenone moiety in the resulting cyclization product [13C]-2. We conclude that there is a distinct preference for hydrogen migration in the acetylene → alkylidene carbene isomerization (A → B) which precedes the cyclization step (B → C). No evidence was found for a fast reversibility of this isomerization (A ⇄ B) involving both acetylenic substituents.
    Additional Material: 1 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1163-1171 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (1RS, 5SR)-2,2,5-Trimethylcyclopentane-1-carboxylic acid (17) and (1r, 2RS, 5SR)-1,2,5-trimethylcyclopentane-1-carboxylic acid (19) are the starting materials for the α-alkynone routes to (±)-capnellene and for similar efforts towards ptychanolide. Since 17 and 19 have, so far, been available only by a branching reaction from the same precursor, the cyanohydrin mixture 2/3, a modified synthesis for 17 and a new one for 19 was developed (Scheme 1). The common precursor 2/3 was treated with POCl3 which effected normal dehydration to 6 (47%, major path) in competition with Me migration to 8 and 9 (17%). The minor path to 8 and 9 could be reduced to 3% when SOCl2 was used for the dehydration of 2/3. This reaction was the basis for an improved synthesis of 17 from 1, using the steps b, e, i, r, and v see Scheme 1 in an overall yield of 35%. The POCl3 reaction was also studied with the pure cyanohydrins 2 and 3, the configurations of which were determined by an X-ray analysis of 2. Me migration did not occur form 2 but only from 3 (25%), which has HO—C(1) and H—C(5) in a cis position. With SOCl2, 3 underwent only 5% Me migration. The new synthesis of 19 started with 4 using the steps h, n, p, and s (see Scheme 1) in an overall yield of 68%.
    Additional Material: 1 Ill.
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  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Butanolides and Butenolides by Intramolecular Ene-Reaction during Thermolysis of Propargyl PropiolatesGas-phase flow thermolysis of 2-butynyl propynoate (1) and 2-propynyl 2-butynoate (2) at 550° afforded 3-ethynyl-2-methyl-2-buten-4-olide (4, 85%) and 2-ethynyl-3-methyl-2-buten-4-olide (5, 80%), respectively. Their formation presumably entails an ene reaction between the methylacetylenic and the acetylenic functions of the diyne esters 1 and 2 to give the two methyliden-vinyliden-butanolides 10 and 11 as intermediates, followed by a [1,5]-H shift to 4 and 5. At 400-450°, the gas phase flow thermolysis of 1 and 2 led to the dimers 16 (77%) and 17 (6%), respectively. These products resulted from the Diels-Alder dimerization of the above mentioned intermediates 10 and 11. The regioselectivity of this dimerization is determined by a ‘head-to-head’ approach, with the double bond conjugated to the carbonyl group acting as the dienophile in both cases. The low yield of 17 from 2 is probably due to a further Diels-Alder reaction of the dimer 17 with its precursor 11, yielding a trimer 18 (8% isolated). This process is not possible when starting with 1, which explains the higher yield of 16. The gas phase flow thermolysis of 2-butynyl 2-butynoate (3) at 550° afforded a mixture of four isomeric products, namely the two monocyclic ethynyl-butenolides 6 and 7 and the two bicyclic vinyl-butenolides 8 and 9. The formations of 6-9 are also rationalizable by initial ene-reactions, in this case two alternative ones, each involving one of the two CH3 groups of 3. This leads to two alkylidene-vinylidene-butenolides, namely 12 and 13. A [1,5]-H shift converts 12 into 6 and 13 into 7. A competing alternative [1,5]-H shift transforms both 12 and 13 to the triene 14, which electrocyclizes to the cyclohexadiene 15. The latter undergoes two alternative [1,5]-H shifts to yield 8 and 9.
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