ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

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
    ISSN: 0947-3440
    Keywords: Bicyclopropylidene ; Spiro compounds ; Cycloadditions ; Amino acids ; Cuprates ; Tetrahydropyridines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of ethyl 2-acetoxy-2-diphenylmethyleneaminoacetate (1) with organocopper reagents derived from bicyclopropylidene (2) and methylenecyclopropane (3) are accompanied by an unusual mode of opening of one three-membered ring to give 4-methylene-1,2,3,4-tetrahydropyridine derivatives 8a, 9 in good yields. The cuprate derived from methylenespiropentane (4) reacts with 1 to yield both the normal substitution product 14 (37%) as well as the rearrangement product 15 (34%), while the simple cyclopropylcuprate undergoes substitution to give the protected cyclopropylglycine 16 (75%) without rearrangement. The tetrahydropyridine 8a shows an interesting tautomerism in solution. The 4-cyclopropylidenetetrahydropyridine 15 undergoes an unusual dehydrodimerization to produce two separable rotamers, C2-19 and C1-19, via 18.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1434-193X
    Keywords: Amino acids ; Bicyclopropylidene ; Methylenecyclopropane ; Palladium catalysis ; Zinc reagents ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Palladium-catalyzed cross-coupling reactions of bromo(methylenecyclopropanes) 1c, 2c with the sodium enolate of dimethyl malonate 4a and the chlorozinc enolates of the glycine equivalent (diphenylmethyleneamino)acetate 4c and diethyl malonate 4d, respectively, have been found to proceed with opening of the three-membered ring in each case, to give the corresponding dienyl-substituted CH-acidic compounds 5-7 in moderate to good yields. On the other hand, coupling of bicyclopropylidenylzinc chloride (2d) with diethyl bromomalonate (4e) and the electrophilic glycine equivalent ethyl 2-acetoxy-2-(diphenylmethyleneamino)acetate (4f) gave 7 and 6 in 27 and 29% yield, respectively.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1434-193X
    Keywords: Radical reactions ; Spiro compounds ; Additions ; Sulfides ; Amino acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of thiols 8a-h onto the double bonds of bicyclopropylidene (1) and methylenespiropentane (2) proceeds quantitatively in benzene at 20 to 75 °C in the absence of catalysts or radical initiators to give products 9, 10 with complete retention of both three-membered rings. Methylenespiropentane (2) yields exclusively the anti-Markovnikov adduct 10. The unsubstituted methylene-cyclopropane (3) gives 9% of the ring-opened compound 12 in addition to the anti-Markovnikov adduct 11. The addition of thiols to n-heptylbicyclopropylidene (13), methylenecyclopropylacetic acid (15), and the amino acids 17, 19 containing bicyclopropylidene or methylenespiropentane fragments, does not proceed stereoselectively, though in all cases the mercapto function adds to the double bond with retention of the cyclopropane ring to give interesting new amino acids containing bicyclopropyl and spiropentyl fragments, respectively. The probable mechanism of this thiol addition is discussed in the light of a test with the cyclizing intramolecular addition of 2-(2-methylenecyclopropyl)ethanethiol 27.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1434-193X
    Keywords: Amino acids ; Spiro compounds ; Michael addition ; Copper reagents ; Curtius degradation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic spiropentylglycine (8) has been synthesized by sodium borohydride reduction of benzyl (E/Z)-2-chloro-2-spiropentylideneacetate (5-Bn), nucleophilic substitution of the chlorine in the product 6 with azide and hydrogenolytic deprotection of the resulting 7 (overall yield 15%). An alternative approach to 8 consisted of the coupling of the higher-order cuprate 10, generated by halogen-metal exchange from bromospiropentane (9), with the electrophilic glycine equivalent 11 followed by deprotection (overall yield 47%). Enantiomerically pure (1′-aminospiropentyl)acetic acid [(R)-16] (overall yield 16% from 5-Me) and 1-aminospiropentanecarboxylic acid [(R)-23] (29% from 5-Me) were obtained from the Michael adduct 14-Me of (4R,5S)-4,5-diphenyloxazolidin-2-one (13) and methyl (E/Z)-2-chloro-2-spiropentylideneacetate (5-Me). Racemic 1-aminospiropentanecarboxylic acid (R/S-23) was prepared by rhodium-catalyzed addition of dimethyl diazomalonate to methylenecyclopropane and subsequent Curtius degradation of the halfester 28 via the azide 29 (overall yield 14%). Upon standing in aqueous solution, 23 underwent complete rearrangement to the new 1-amino-2-methylenecyclobutanecarboxylic acid (24). The interesting derivative of azabicyclo[3.1.0]hexane-1-carboxylate 34 with an annelated spiropentane moiety and a β-amino acid fragment was incidentally obtained in a one-step intermolecular domino reaction starting with the addition of lithium benzylamide to methyl 2-chloro-2-cyclopropylideneacetate (32, 41% yield).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 1434-193X
    Keywords: Amino acids ; Bicyclopropylidene ; Methylenespiropentane ; Spiro compounds ; Organolithium derivatives ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic bicyclopropylidenyl- (rac-11) and methylenespiropentyl- (rac-17) substituted alanines have been synthesized by iodination of bicyclopropylidenyl- and methylenespiropentylmethanols 7, 13, nucleophilic substitution of the iodine in 8, 14 with the enolate of ethyl α-(diphenylmethyleneamino)acetate (O'Donnell's glycine equivalent) and deprotection of 9, 15 in 24 and 18% overall yield, respectively. N-Methylbicyclopropylidenylalanine rac-22, was obtained from the Michael adduct of (bicyclopropylidenyl)magnesium bromide 18 to enamine 19 and deprotection of the carbamate 20 (23% overall yield). Racemic (1-amino-2-methylenespiropentane)- (37), (1-amino-2-methylenecyclopropane)- (3), and (1-aminobicyclopropylidene)carboxylic acid (39) were prepared as hydrochlorides by tert-butoxycarbonylation of the lithiated methylenespiropentane (6), methylenecyclopropane (4), or bicyclopropylidene (5) intermediates with di-tert-butyl pyrocarbonate (Boc2O), repeated lithiation of the tert-butyl esters 29, 30, and 33 with LDA and subsequent carboxylation, Curtius degradation of the half esters 31, 32, and 34 followed by deprotection in 11, 45, and 4% overall yields, respectively. Compound 37 was also prepared from bicyclopropylidene (5) following the same procedure, but with rearrangement in the last but one step, in 19% overall yield. An attempted Hofmann degradation of the bicyclopropylidenecarboxamido ester 40 with NBS failed and gave only bromohydrin 44 (27%), but with bis(acetoxy)iodobenzene provided carbamate 46a, b in 76 amd 79% yield, respectively. Along this route with subsequent deprotection of 46b, the amino acid 39 could be prepared in up to 10% overall yield from bicyclopropylidene.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...