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Pyrylium salts azulenes

Azulene, 4,b,8-trimethyl-from pyrylium salts, 3, 660 Azulenes... [Pg.532]

Trimethylpyrylium perchlorate is a very versatile and useful starting material. Thus its reaction with cyclopentadienyl-sodium has made 4,6,8-trimethylazulene 12 easily available for general studies of the properties of azulenes 18 and for the synthesis of related compounds.14 In addition, pyrylium salts are readily converted to a variety of pyridine derivatives 9 15 as well as to derivatives of nitrobenzene16 and phenol.9 17,18 It is clear that its value as a starting material is such that it is receiving wide use. [Pg.122]

Triphenylpyrylium tetrafluoroborate is a versatile and useful stable starting material. Its reaction with nitromethane under basic conditions has made 2,4,6-triphenylnitrobenzene easily available. In addition, pyrylium salts are readily converted to a variety of pyridine derivatives i i . 20 including alkyl- and arylpyridinium salts, to thiopyrylium salts," and to substituted azulenes. ... [Pg.144]

The original literature456,463 should be consulted for alkylation by pyrylium salts and the subsequent reactions then observed (formation of aromatic compounds and azulenes). Cyclizations that occur on intramolecular alkylation have been reviewed by Bestmann.456... [Pg.926]

The formation of azulenes by cyclocondensation of cyclopentadienyl anions is a prime example of a synthesis with pyrylium salts (Hafner 1973 [8], cf 307). Thus, 4,6,8-trimethylazulene 46 is produced by the reaction between 2,4,6-trimethylpyrylium salts and sodium cyclopentadienide, resulting in ring-opening at C-2 (45) followed by ring closure of the cyclopentadienyl system 47 which is a probable intermediate. [Pg.229]

The photophysical properties of polyacene molecules depend markedly on the number of rings and the fluorescence behaviour of hexacene has now been compared with that of earlier members of the series. A similar comparison has been made of the photophysical properties of catacondensed aromatic poly-cycles. Fluorescence from an upper-excited singlet state has been described for benz[a]azulene derivatives while the fluorescence properties of some antiaromatic molecules have been described in detail. Several thiopyrylium and pyrylium salts have been studied and the effects of various substituents attached to the heterocycle have been examined in terms of the triplet yield. A full evaluation of the photophysical properties of 4-aminonaphthalimide, and its... [Pg.19]

A further modification [20] uses a pyrylium salt instead of a pyridinium salt as starting material. For example 4,6,8-trimethyl-azulene was prepared in 65% yield from cyclopentadiene and 2,4,6--trimethylpyrylium perchlorate ... [Pg.187]

The reaction proceeds readily at room temperature and intermediates can only be isolated if the reaction is carried out below -20°. The reaction is not successful starting from unsubstituted pyrylium perchlorate. Pyrylium salts havealso been converted into azulenes by opening the heterocyclic ring with methylaniline and letting the resultant product react with sodium cyclopentadienide [21]. [Pg.187]

Using one or other of these methods starting from pyridinium or pyrylium salts a large number of azulene derivates has been readily prepared.(See for example, [15].)... [Pg.187]

In the Hafner azulene synthesis, pyrylium salts are subjected to cyclocondensation with cyclopentadienyl anions thus 4,6,8-trimethylazulene (50) is obtained from 2,4,6-trimethyl pyrylium salts and Na-cyclopentadienide via intermediates 48/49 (cf also p. 379). [Pg.304]

A close study of deuteriated azulenes showed that, in the mass spectrometer, 72% of ions suffer complete hydrogen scrambling prior to expulsion of —CH2—. The rearranged ions are the same as those in the spectrum of naphthalene. The reaction of sodium cyclopentadienide with pyrylium salts has been used to make several more azulenes, e.g. (24), and chlorination of 4,6,8-trimethylazulene in H2SO4 has been studied. ... [Pg.222]


See other pages where Pyrylium salts azulenes is mentioned: [Pg.244]    [Pg.25]    [Pg.660]    [Pg.208]    [Pg.660]    [Pg.208]    [Pg.122]    [Pg.244]    [Pg.415]    [Pg.583]    [Pg.441]   
See also in sourсe #XX -- [ Pg.14 ]




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