Intramolecular Aza-Wittig Routes to Sydnoquinoxalines

Burson, William; Jones, David R.; Turnbull, Kenneth; Preston, Peter N.

doi:10.1055/s-1991-26564

Cited by 20 publications

(6 citation statements)

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“…As further examples, the sydnone ring is brominated in preference to a pyrazolyl system at C3, while nitration of 3-methyl-4-phenyl sydnone affords the 4-nitrophenyl substituted derivative. Intramolecular electrophilic substitutions at C4 provide a route to fused sydnones such as 73 [86] and 74 [87]. Electrophiles have also been introduced at the 4-position through organometallic derivatives.…”

Section: Ring Cleavagementioning

confidence: 99%

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Oxadiazoles

Romeo¹,

Chiacchio²

2011

Modern Heterocyclic Chemistry

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Section: Ring Cleavagementioning

confidence: 99%

“…The phenyl rings are tilted to the same side with respect to the oxadiazole ring and the angle between them is 8. 86 . An interesting aspect of the crystal structure is the presence of two weak CÀHÀO bonds between two neighboring molecules in the same layer.…”

mentioning

confidence: 99%

Oxadiazoles

Romeo¹,

Chiacchio²

2011

Modern Heterocyclic Chemistry

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“…[20][21][22] Consequently, chemists still enthusiastically pursue the syntheses of sydnone derivatives. [23][24][25][26][27][28] Following reports of these activities, this study seeks to synthesize a series of pyrazolines that contain the sydnonyl moiety, with the aim of obtaining new biologically active compounds.…”

Section: Heterocyclic Analogues Of Chalcones Have Been Preparedmentioning

confidence: 99%

A Concise Synthetic Method for Sydnonyl-Substituted Pyrazoline Derivatives

Shih¹

2003

Synthesis

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The pyrazolines have been found to have diverse applications in medicine. They are known to be potent antibiotic or antioxidizing agents. Two types of sydnonyl-substituted a,bunsaturated ketones were synthesized by the Claisen-Schmidt condensation for the preparation of sydnonyl-substituted pyrazolines. One is the condensation of 3-(4-ethoxyphenyl)-4-formylsydnone (1) with acetone (2a) or acetophenone (2b), and the other is the condensation of 4-acetyl-3-arylsydnones 5 with various aryl aldehydes 6. Finally, 1H-pyrazoline derivatives 8 were synthesized successfully by reacting the appropriate a,b-unsaturated ketone precursors 7 with hydrazine hydrate.Heterocyclic analogues of chalcones have been prepared for biological studies. The a,b-unsaturated ketones can play as versatile precursors in the syntheses of the corresponding pyrazoline derivatives. 1-5 Moreover, the pyrazolines have been found to have diverse applications in medicine and agriculture. In particular, they are reported to be potent antibiotic and antioxidizing agents. 1-9 Hence, methods for generating this type of heterocycle are very attractive. 10-19 Several sydnone derivatives are associated with a wide range of physiological activities including antimicrobial, anti-inflammatory, analgesic and antipyretic activities. 20-22 Consequently, chemists still enthusiastically pursue the syntheses of sydnone derivatives. 23-28 Following reports of these activities, this study seeks to synthesize a series of pyrazolines that contain the sydnonyl moiety, with the aim of obtaining new biologically active compounds.The pyrazolines are usually prepared by the reactions of of a,b-unsaturated ketones and hydrazine hydrate. Although well known, this reaction has never been applied to the sydnone systems. Prompted by the biological activities of heterocyclic compounds and earlier interest in incorporating heterocyclic moieties in sydnones, [29][30][31][32][33][34][35] it was contemplated to synthesize some new sydnones that have pyrazolinyl moieties. In this present study, 4-[3-(4-ethoxyphenyl)sydnon-4-yl]but-3-en-2-one (3a) or 3-[3-(4-ethoxyphenyl)sydnon-4-yl]-1-phenylprop-2-en-1-one (3b) were prepared in high yields from the reaction of 3-(4-ethoxyphenyl)-4-formylsydnone (1) with acetone (2a) or acetophenone (2b) by the Claisen-Schmidt condensation 36,37 (Scheme 1). Treatment of compound 3a or 3b with hydrazine hydrate in 95% ethanol under various temperature conditions did not yield the desired cyclization product 4 (Scheme 1) though a crude solid was isolated. This condensation solid product was characterized as a hydrazone of compound 3 according to the IR and NMR analyses. This result implied that the electron-releasing property of 4-sydnonyl group may increase the electron density on the carbon-carbon double bond of a,b-unsaturated ketones and hinder the Michael addition of hydrazine to the a,bunsaturated ketones 3. Scheme 1 1: Ar = p-C 2 H 5 OC 6 H 4 ; 2a: R¢ = CH 3 ; 2b: R¢ = C 6 H 5To solve this problem, another type of sydnonyl-substituted a,b-unsaturat...

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“…8,9 In this regard, it has been speculated by Coburn and O'Donnell that, in fused-ring sydnones, the stabilization achieved by the additional conjugation from the sydnone ring "might be of practical significance, since many of the simple sydnones with potentially useful biological activities lack thermal stability and frequently darken upon exposure to light and air". 10 While, previously, sydno [3,4-a]quinoxalines were prepared by Coburn and O'Donnell using a lithiation protocol, 10 for us the most effective, general strategy to fused-ring sydnones has been to generate an electrophilic side-chain that can be trapped by the heteroaromatic sydnone ring.…”

Section: Introductionmentioning

confidence: 99%

“…10 While, previously, sydno [3,4-a]quinoxalines were prepared by Coburn and O'Donnell using a lithiation protocol, 10 for us the most effective, general strategy to fused-ring sydnones has been to generate an electrophilic side-chain that can be trapped by the heteroaromatic sydnone ring. In this fashion, we have synthesized a sydno [4,3-c]benzotriazine, 9 several 4-arylaminosydno[3,4-a]-quinoxalines, 8 and a limited number of 5-substituted sydno [3,4-a]quinazolines. 11,12 In order to explore further this concept, and extend the limited range of fused-ring sydnones available, we elected to examine the reactions of o-alkynylphenylsydnones 1 (prepared by Sonogashira coupling with o-iodophenylsydnone) 13 with various acids in the expectation that sydnoquinoline derivatives 2 would result.…”

Section: Introductionmentioning

confidence: 99%