Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 621-624 
    ISSN: 0170-2041
    Keywords: 6H-1,2-Oxazines ; γ-Lactams ; Lewis acids ; Ring contraction ; Phosphite, trimethyl ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unexpected Formation of γ-Lactams from 6H-1,2-Oxazines Promoted by Lewis AcidsThe reaction of 6H-1,2-oxazine 1 with trimethylsilyl cyanide in the presence of titanium tetrachloride provides α,β-unsaturated γ-lactam 3. Similarly, Lewis acid-promoted addition of trimethyl phosphite towards 1 affords a mixture of γ-lactams 8 and 9. The structure of 9 was established by X-ray analysis. A plausible mechanism for the formation of these γ-lactams by Lewis acid-induced ring contraction is proposed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 0170-2041
    Keywords: Cyclopropanes ; Enolate alkylation ; Michael addition ; Cyclization, acid catalyzed ; Reduction, ionic ; Steroids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthese of Estrone Derivatives from Siloxycyclopropanecarboxylic Acid EstersSyntheses of new rac-estrone analogues such as 10, 19, 21 and 22 are reported. Key intermediate 3 has been efficiently prepared by alkylation of the lithium enolate of the methyl cyclopropanecarboxylate 1 employing 2 as electrophile. One-pot ring opening/Michael addition procedures have been developed to convert 1 and 3 into polyfunctionalized compounds 5, 7, 8, and 9. Diketo diester 8 can be cyclized with acid to give tetracyclic dienes which are immediately reduced by triethylsilane under acidic conditions providing steroid derivatives 10 and 11. Depending on the purification method, in addition to 10/11 the isomer 12 and the oxidized products 13/14 have been isolated. The structures of 10 and 13 have been confirmed by X-ray analyses. Acid-induced cyclization of precursor 9 affords the tetracyclic diene 19 and the pentacyclic lactone 20. Catalytic hydrogenation of the diene 19 provides the estrone derivative 21 in good yield, but with the unnatural cis-C/D-ring junction. Ionic reduction of 19 gives the steroid derivative 22 together with the alcohols 23.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1988 (1988), S. 997-1000 
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycosyl bramides and selenides 1 react with hexamethylditin to give coupling products 2-4 in 32% yield. The reactions occur by dimerization of glycosyl radicals, the radical 8 in the 4C1 chair conformation being slightly more stereoselective than the glucosyl radical 7 in the B2,5 boat conformation.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective Formation of Oxaspiropentanes and of Spiropentyl Ketones. On the Stereochemistry of Nucleophilic Substitution at CyclopropanesIn an intramolecular SN2-type substitution with formation of the spiro[2.2]-pentane skeleton, the highly strained transition state 2 with one three membered ring in an equatorial/equatorial and one in an apical/equatorial position of a pentacoordinated carbon atom ought to be - at least formally - involved. Yet, several examples of such processes are known. With the endo/exo isomeric bromohydrines 4 and 5 and bromoketones 13 and 14 this reaction is now shown to occur with clean inversion of configuration at the cyclopropane carbon atom. Unambiguous configurational assignments are made by X-ray crystal structure determinations of the 7′exo-bromo-benzoate 6 (from the bromohydrine 4), of the endo-sulfonate 12 (from oxaspiropentane 7, formed from 4), of the 7exo-bromonorcarane 13, and of its cyclization product 15. - A comparison of the qualitatively measured rates of epoxide ring formation from the closely related systems 18 and 20 proves the expected slower substitution at the cyclopropane carbon atom as compared to the open chain analogue.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 60 (1977), S. 1151-1154 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New results concerning the mechanism of retentive substitution at the three membered ring of propellanesThe reaction of the endo- and exo-bromide 1a and 1b with acetate ion in aprotic polar solvents carried out at high concentrations of 1 furnishes the dimeric dehydro-halogenation products 3a and 3b, the structures of which are determined by x-ray crystallography (Fig. 1). The formation of 3a and 3b as well as of the products 2 of a retentive substitution process can be explained by assuming that the strained benzo-tropones 4 are intermediates. Their high barrier to inversion is confirmed by π-SCF-molecular mechanics calculations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 0170-2041
    Keywords: Chasmanthin ; Palmarin ; Palmatoside A and B ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of palmarin (1) has been determined by X-ray diffraction. The ring C conformation was confirmed to be that of a half chair, and the same result was obtained from 1H-NMR spectrometry. The ring C of chasmanthin (2) and glucosides of 1 and 2 (palmatoside A, and B) was also decided as a half boat by analysis of the 1H-NMR spectra.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1989 (1989), S. 527-531 
    ISSN: 0170-2041
    Keywords: Dehydroalanine esters, N-(arylmethylene)- ; Tetrahydropyridines ; 3,6-Diazabicyclo[3.2.1]oct-2-enes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: On the Dimerization Reaction of N-(Arylmethylene)dehydroalanine Methyl EstersN-(Arylmethylene)dehydroalanine esters are highly reactive compounds. They dimerize in a [4 + 2] cycloaddition reaction (Diels-Alder reaction) yielding rac-3,4,5,6-tetrahydropyridine derivatives 2 Which can be isolated under suitable conditions. In solution the dimers 2 tautomerize to give the enamines 3 which subsequently undergo a fast intramolecular cyclization reaction yielding the bicyclic compounds. 4. These 3,6-diazabicyclo[3.2.1]oct-2-ene derivatives 4 are formed diastereoselectively. The structure of 4 was established by X-ray analysis. The bicyclic diaminodicarboxylic esters 4 represent the stable final products of this series of transformations.
    Notes: N-(Arylmethylen)dehydroalaninester sind hochreaktive Verbindungen. Sie dimerisieren unter [4+2]-Cycloaddition (Diels-Alder-Reaktion) zu rac-3,4,5,6-Tetrahydropyridin-Derivaten 2, die unter geeigneten Bedingungen isoliert werden können. In Lösung tautomerisieren die Dimeren 2 zu Enaminen 3, die schnell intramolekular zum Bicyclus 4 reagieren. Diese 3,6-Diazabicyclo-[3.2.1]oct-2-en-Derivate 4 werden diastereoselektiv gebildet. Ihre Struktur wurde durch Röntgenstrukturanalyse geklärt. Die bicyclischen Diaminodicarbonsäureester 4 stellen die stabilen Endprodukte der gesamten Reaktionsfolge dar.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cyclic Conjugated 5- and 7-Membered Ring Systems,. - Synthesis and Structure of α-(6-Fulvenyl)dibenzo[a,e]heptafulveneSynthesis, physical properties, and the results of an X-ray analysis of the title compound are reported. The hydrocarbon has a boat-shaped 7-membered ring and a pronounced alternance of bond lengths.
    Notes: Es werden Synthese, physikalische Eigenschaften und Ergebnisse der Röntgenstrukturanalyse der im Titel genannten Verbindung beschrieben. Der Kohlenwasserstoff weist einen bootförmigen 7 gliedrigen Ring und deutliche Bindungsalternanz auf.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...