Oxazolo[3,2‐<i>a</i>]pyridinium salts

Bradsher, Charles K.; Zinn, Mary F.

doi:10.1002/jhet.5570040111

Cited by 30 publications

(14 citation statements)

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“…It is also well known, that in sulfuric acid the compound XlVa undergoes closure of the oxazolium ring forming 2-phenyloxazolo[3,2-a]pyridinium cation Xb [12]. We found that the conversion of mesoionic derivative XII to cation Xb may proceed as one-pot recyclization [13] with the yield 83%, and the structure of the perchlorate Xb was confirmed by X-ray data.…”

Section: Structure Of B-fused Munchnonessupporting

confidence: 68%

Fused munchnones in recyclization tandems

Бабаев

2000

Journal of Heterocyclic Chem

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Mesoionic azolopyridines of the general formula I are related to the family of condensed munchnones [1].Although the chemistry of b-fused oxazolones la [2] and imidazopyridine derivatives Ib [3] is well reviewed, no data are reported yet about the synthesis of the mesoionic thiazolopyridines Ic-e. In the first part of this review we discuss novel strategy to the synthesis of condensed thiazoles Ic-e and describe structural features of munchnones la and Ic for which we report X-ray data for the first time. In the second part we introduce the concept of recyclization tandems: Mesoionic system la may be easily transformed to highly reactive oxazolo[3,2-a]pyridinium cation which, in turn, undergoes variety of ring opening/transformation reactions leading to novel classes and subclasses of heterocyclic compounds. Synthesis of Novel b-Fused Munchnones.Krohnke first attempted to prepare mesoionic thiazoles Ic by cycloaddition of carbon disulfide to pyridinium and isoquinolinium ylides [4]. Although in the case of isoquinolines IIa the desired mesoionic product IIIa was obtained, the reaction of pyridinium salt IIb led only to the stabilized compound IIlb and not to the parent munchnone.This result can be clearly explained in terms of higher electron deficiency of the isoquinolinium than that of the pyridinium ring. The presence of a leaving group at a-position of the initial pyridinium salt would favor cyclization. We found that 2-chloropyridinium salts IVa,b in reaction with carbon disulfide at room temperature form the desired mesoionic thiazolopyridines Va,b [5]. Structure of the compound Va was confirmed by X-ray analysis.Analogous reaction between carbon oxosulfide and the salt IVa led to another mesoionic system VI; the yield, however, was low (<10%), and we performed a multistep synthesis of compound VI starting from the available 2-bromopyridinium salt VII [6].

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Section: Structure Of B-fused Munchnonessupporting

confidence: 68%

Fused munchnones in recyclization tandems

Бабаев

2000

Journal of Heterocyclic Chem

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“…The sole described example is the synthesis of angular salt 4a on using 1-methoxyisoquinoline (7a) [10]. The homologous salt 4b is unknown, and information on linear tricyclic system 3 is generally absent from the literature.…”

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confidence: 99%

“…The N-phenacylation of 1-methoxyisoquinoline 7a in low yield (~8%) has been described [10]. Examples of the N-alkylation of the homologous isoquinolone 6b or the methoxy derivative are unknown, although an unusual intramolecular N-alkylation, accompanying O-demethylation, for the structurally analogous 1-methoxy-3-(ω-bromopropyl)isoquinoline has been described [15] There are few examples of N-alkylation among derivatives of 3-isoquinolone 8a and also of 3-methoxyisoquinoline 9a.…”

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confidence: 99%

“…It is possible to obtain bicyclic salts 1 and their (cyclo)homologs (R = H, Me, RR 1 is the cycloalkane fragment) [2]. A tricyclic oxazoloquinoline was synthesized on using 2-methoxyquinoline [10].…”

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confidence: 99%

“…The standard route of building up an oxazole ring on a pyridine at the C-N bond comprises N-phenacylation of alkaline salts of pyridone 5a [8,9] or methoxypyridines 5b [2,10] (according to Bradsher) with subsequent acid cyclocondensation. It is possible to obtain bicyclic salts 1 and their (cyclo)homologs (R = H, Me, RR 1 is the cycloalkane fragment) [2].…”

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confidence: 99%

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