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  • Chemistry  (2)
  • 33.80.Eh
  • 1990-1994  (2)
  • 1990  (2)
  • 1
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of New Heptafulvenes; X-Ray Analysis of ‘8,8-(1′,4′-Dioxotetramethylene)heptafulvene’ (2-(Cyclohepta-2,4,6-trien-1-ylidene)cyclopentane-1,3-dione)Experimental procedures for the synthesis of heptafulvene (3a), 8,8-tetramethylene heptafulvene (3c) and ‘8,8-(1′,4′-dioxotetramethylene) heptafulvene’ (2-(cyclohepta-2,4,6-trien-1-ylidene)-cyclopentane-1,3-dion; 3d) are described. The most important sequences include a low-temperature reaction of tropylium salts with lithium or Grignard carbenoids (Scheme 1) to give 3a and 3b as well as hydride abstraction from substituted cycloheptatrienes followed by deprotonation to give 3c and 3d. Limitations of these sequences are discussed. Two other heptafulvenes 3h and 3i are available by silylation of heptafulvenolates according to well-known procedures. NMR-Spectroscopic evidence as well as an X-ray analysis of 3d are presented. Compound 3d is a relatively polar heptafulvene with a planarised seven-membered ring as well as a partly delocalized π system.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0009-2940
    Keywords: Polymethine dyes, chiral / Indocarbocyanines / Cyanines ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis, Structure, and Properties of Novel Chain-Substituted and Chiral Trimethine Cyanine Dyes with Indoline End GroupsSynthesis and spectroscopic properties of the trimethine cyanine dyes 3, 8a, b, and 13a, b as well as 14a-c with new substitution patterns are described. Constitutions and configurations of 3, 8a, b and 14c have been determined by X-ray analyses (Figures 1, 2, and 6). Dye 3 exists in the previously unknown di-cis (E, E, Z, Z) configuration along the methine chain. Attempts to prepare 3 in a base-catalysed reaction unexpectedly led to the rearranged trimethine cyanine dyes 8a, b with a centre of chirality in one of the indoline end groups. Using this Wagner-Meerwein rearrangement after resolution, the chiral heterocyclic quaternary salts (S)-12a- c have been prepared, from which the optically active trimethine cyanine dyes (S,S)-14a-c have been obtained for the first time. The UV/VIS spectra of 3, 8a and 13a (Figure 7) as well as the CD spectra of 12a and 14a (Figures 3 and 4) are compared and discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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