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  • 1
    Electronic Resource
    Electronic Resource
    Sterically Congested Molecules, 17Part 16: Ref.[1].. - Novel Syntheses of α,α,β-Tri-tert-butyl Compounds (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 193-202 
    Details
    ISSN: 0947-3440
    Keywords: Acyloins ; Barbier reaction ; Epoxidations ; Glycols, deoxidation ; Tri-tert-butyl compounds ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pivaloin (2), prepared from ethyl pivalate (1) or from dimethyl oxalate (3), reacts with tert-butyllithium by reduction (45% of 10) and addition (45% of 9), whereas the corresponding Barbier variant takes a different course. Productive transformations of the α,α,β-tri-tert-butyl glycol 9 lead to α,β,β-tri-tert-butylethanone (17, overall 4 steps), or α,α,β-tri-tert-butylethene (20, 3 or 4 steps), or α,β,β-tri-tert-butyl-β-hydroxyethanone (19, 3 steps, also by Grignard addition to bipivaloyl 4). Steric congestion is assessed by searches for restricted internal rotation. The alkene 20 and its epoxide 27 are studied with respect to NMR assignments and chemical degradation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970128
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  • 2
    Electronic Resource
    Electronic Resource
    Cyclopropan-Derivate, 3. (1-Alkylcyclopropyl)ketone durch Acylierung von α-substituierten γ-Lactonen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2167-2172 
    Details
    ISSN: 0009-2940
    Keywords: Acylation ; Ketones ; γ-Lactones ; Butanolides ; Cyclopropyl compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclopropane Derivatives, 3.  -  (1-Alkylcyclopropyl)ketones by Acylation of α-Substituted γ-LactonesThe 2-acylation of 2-substituted 4-butanolides 2 is moderately sensitive to steric crowding, whereas the subsequent ring- opening of 2-acyl-2-alkyl-4-butanolides 4, 11 to give-chloro ketones 6, 12 by chloride-transferring acid derivatives be-comes difficult with bigger lactone substituents. Similar observations pertain to the preparation of y-chlorobutanoyl chlorides 10 from 2-alkyl-4-butanolides 2. The proper choice of the starting 4-butanolides (2a, b or 14 but not 2c) provides for an indirect coupling of two different lactones to y,y-dichloro ke-tones 12. Dicyclopropyl ketones 13 with variable patterns of substitution may thus be prepared from 4-butanolides in a direct manner with global yields exceeding 50% and without purification of intermediate products (except for acid chlorides like 10).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231113
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  • 3
    Electronic Resource
    Electronic Resource
    Cyclopropan-Derivate, 2. Selbst-Acylierung der α-Alkyl-γ-lactone zu Herstellung von Bis(1-alkylcyclopropyl)ketonen über Spiro[4.4]acetale (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2161-2166 
    Details
    ISSN: 0009-2940
    Keywords: Acetals ; Ketones ; γ-Lactones ; Butanolides ; Spiro compounds ; Cyclopropyl compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclopropane Derivatives, 2.  -  Self-Acylation of α-Alkyl-γ-lactones To Give Bis(1-alkylcyclopropyl)ketones via Spiro[4.4]acetalsHigh-yield synthetic ways are recommended for the title lactones 1.The coupling of two 2-alkyl-4-butanolides is possible in an inter-(1b, c) or intramolecular fashion (4c) to give spiro[4.4] acetals 8 or 9 respectively, in the absence of hindering substituents. Symmetrically substituted bis(1-alkylcyclopropyl)ketones 12 and 13 may be prepared by acidic cleavage of those spiro[4.4] acetals lacking 2,7-substituent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231112
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  • 4
    Electronic Resource
    Electronic Resource
    (E,Z)-Gleichgewichte, 15. Synthesen und erhöhte Konfigurationslabilität von 2-Iminoindan-Derivaten mit Vorderseitenspannung (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 2041-2049 
    Details
    ISSN: 0009-2940
    Keywords: Basicity ; Diastereotopomerization, (E/Z) ; Imines ; Steric shielding ; Steric strain ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (E,Z) Equilibria, 15[1]. - Syntheses and Lability of the Configuration of 2-Iminoindan Derivatives with Front StrainSyntheses and properties are described for sterically shielded imines R2C = NR (3c, e, g-k), which are rather inert toward nucleophiles. Nucleophilic attack at the nitrogen atom of 3k is indicated by the formation of the azine 4. (E,Z) Configurational diastereotopomerization (anti/syn) is strongly dependent on N substituents [CH3, phenyl, 1-naphthyl, acetyl, Si(CH3)3, cyano, SC6H5, SOC6H5, SO2C6H5, and nitro]. It is accelerated by front strain along the C—N bond in 3a-c, e, g, h, j, and k and provides an energetic basis (by ΔG≠ and ΔΔG≠ values) for the gauging of force-field parameters. This (E,Z) stereo-mutation is characterized by a vanishing solvent dependence and a positive volume of activation (+10.2 cm3 mol-1 for 3a). In contrast to other π acceptor substituents, the N-nitro group in 31 retards (E,Z) interconversion.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250912
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  • 5
    Electronic Resource
    Electronic Resource
    (E,Z) Equilibria, 14. Substituent-Induced Chemical Shifts along the C = N Bond of Schiff Bases (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 2033-2040 
    Details
    ISSN: 0009-2940
    Keywords: 13C NMR, SCS ; Substituent effects ; Imines ; Isomerization, (E,Z) Schiff bases ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sterically congested N-(1,1,3,3-tetraalkyl-2-indanylidene)-amines 8-11, N-(cyclopentylidene)anilines 13-17, and two of their salts are described, together with a short synthesis of 2-imino-1,1,3,3-tetramethylindan (5). Some of these imines show rapid (E,Z) equilibration. Positively and negatively charged nitrogen functions (in 6 and 7) cause opposite 1H- and 13C-NMR chemical shift effects along the C = N bond. Chemical shifts are almost equally affected by the lone electron pair and by the imino N-H bond. Substituent-induced chemical shifts (SCS) have been assigned for all syn and anti positions with respect to methyl, phenyl, and 2,6-dimethylphenyl groups at the imino nitrogen atom. The structurally well-defined, rigid imines recommend themselves as new models for the calibration of theoretical approaches to syn/anti-differentiating SCS.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250911
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  • 6
    Electronic Resource
    Electronic Resource
    (E, Z)1-Equilibria, 17 Demonstration of the Nitrogen Inversion Mechanism of Imines in a Schiff Base ModelDedicated to Professor Heinrich Nöth on the occasion of his 65th birthday. (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 747-754 
    Details
    ISSN: 0009-2940
    Keywords: Diastereotopomerization, (E, Z) ; Imines ; Inversion, nitrogen ; Permethylation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental differentiation between pure C=N double bond rotation and nitrogen inversion in N1-arylimines is possible with a single compound (13b) under the proviso of slow rotation about the N-aryl single bond. Labelling by 1H and 13C nuclei at the diastereotopic faces of the C=N moiety as well as of the N-aryl group is the clue to a successful stereodynamic analysis, as performed by variable-temperature NMR spectroscopy of 13b, a sterically congested and chiral model compound. Interpretation of similar measurements on a second model (13d) is less straightforward. The experimental observation of time-averaged Cs symmetry by NMR coalescences is only compatible with a mechanism of (E/Z) stereomutation either by pure inversion at sp2 nitrogen or by a contribution from C=N rotation together with a synchronized (geared) controtation about the N-aryl single bond. However, the latter combination is concluded to be predominantly inversion-like by comparisons with related imines.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260327
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  • 7
    Electronic Resource
    Electronic Resource
    (E,Z) Equilibria, 12. Differential NMR Shielding by Phenyl, Assigned from Chemical Labelling and (Z,E) Equilibration (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 1137-1141 
    Details
    ISSN: 0009-2940
    Keywords: Allyl anion ; Differential NMR-shielding ; Schiff's bases ; Stereoselective substitution ; Isomerization, (Z,E) ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unequivocal NMR assignments of the (E,Z) isomeric pairs 3 and 8 are possible by (Z,E) equilibration. Deprotonation of 2-methyl-1-phenylpropene (1) with n-BuLi under any conditions gives only a single allyl-metal derivative 2. Methylation of the latter gives the isomer (Z)-3, while deuteriolysis leads to the isotopically labelled derivative 6 of the olefin 1; this Proves the NMR assignments for 1 as well as the endo configuration of 2. The phenyl group gives rise to a differential shielding effect on the γ-carbon nuclei in methyl and methylene gropus along a CC double bond (ca, 7 ppm), and this effect is comparable to that along a CN double bond as in 8. The nitrile function in 5c is much less effective.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901230529
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  • 8
    Electronic Resource
    Electronic Resource
    Erschöpfende α-Alkylierung von Fünfring-Ketonen mit Natriumhydrid und Dimethylsulfat oder Ethyliodid (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 1791-1793 
    Details
    ISSN: 0009-2940
    Keywords: Cycloalkanones ; Dimethyl sulfate ; Peralkylation ; Sodium hydride ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Exhaustive α-Alkylation of Five-Membered Ring Ketones by Sodium Hydride and Dimethyl Sulfate or Ehtyl IodideCα-Permethylation may be carried out by addition of a basesensitive ketone like cyclopentanone to the inexpensive and stable mixture of sodium hydride and dimethyl sulfate. Exhaustive Cα-ethylation is exemplified with sodium hydride by simultaneous introduction of ketone 4 and ethyl iodide. The 13C-NMR absorptions of 1,3-alkylated 2-indanones 3-5 are assigned and some of the CH coupling constants reported.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891220927
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  • 9
    Electronic Resource
    Electronic Resource
    Substituent-induced chemical shifts along C=C double bondsSterically Congested Molecules, Part 8. For Part 7, see Ref. 6. (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 557-565 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; 1H NMR Olefins ; Substituent effects ; Substituent-induced chenical shifts (SCS) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H and 13C NMR signals were assigned and CH coupling constants (1J, 2J, 3J) determined for a series of α-mono-and α,α-disubstituted (1,1,3,3-tetramethyl-2-indanylidene)methanes with the following α-substituents: (mesityl)2B, n-propyl, phenyl, tert-butyl-C(=NH), cyano, (tert-butyl)2C(OH), pivaloyl, H2N-CO, PhNH-CO, carboxy, ritro, acetoxy, Me3SiO, Me3Si, PhS, PhSMe+, PhSO, PhSO2, bromo and trimethylstannyl. The 1J couplings with the olefinic proton span the range 124.3-193.7 Hz. Substituent-induced chemical shifts (SCS) of most of the nuclei with respect to the α-unsubstituted olefin obey simple additivity in the α,α-disubstituted compounds and are very similar to the SCS values along the C=N double bond in the isoelectronic (1,1,3,3-tetramethyl-2-indanylidene)amines within the error limits. The exceptions concern nuclei in the immediate vicinity of the perturbing substituent. A dominant mechanistic contribution of electric field effects appears likely for the more distant aromatic part of the indanylidene moiety. The chemical shifts of two (2,2,5,5-tetramethylcyclopentylidene)methanes are shown to be compatible with the SCS parameters from the indanylidene series.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260310608
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  • 10
    Electronic Resource
    Electronic Resource
    Substituent-induced chemical shifts (SCS) by the phenyl group in sterically congested styrene derivativesSterically Congested Molecules, Part 7. For Part 6, see R. Knorr et al., Chem. Ber. 126, in press (1993). (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 388-393 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; 1H NMR ; 9-Methylenefluorenes ; Substituent effects ; Substituent-induced chemical shifts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two 13C NMR methyl signals of the sterically congested 9-benzylidene-1,8-dimethylfluorene (1a) have the surprisingly small separation of only 0.37 ppm; for 9-benzylidene-2,7-dimethylfluorene the corresponding methyl separation is 0.04 ppm. An alternative analysis of 1a with respect to 1,8-dimethylfluorene shows that the perturbing syn-phenyl substituent has caused a downfield ( + 0.47 ppm) 13C shift but an upfield 1H shift ( - 0.97 ppm) of the compressed 1-CH3 group. For further comparisons, NMR assignments were also made for 2,7-dimethylfluorene, 1,8-dimethylfluoren-9-one and 2-(1,1-dimethylethyl)-3,3-dimethyl-1-phenylbut-1-ene.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260310415
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