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Pyrroles 4-alkyl oxazolones

Alkyl(aryl)-2-(trifluoromethyl)-5(277)-oxazolones have been used as intermediates to prepare 2-(trifluoromethyl)pyrroles interesting compounds frequently used as insecticides and acaricides. The oxazolones react with electron-dehcient unsaturated compounds in the presence of a base. Reaction of 5(277)-oxazolones, usually with a substituted aryl ring at C-4, with a wide variety of alkynes and alkenes has given rise to numerous 2-(trifluoromethyl)pyrroles 56. For example,... [Pg.143]

Mesoionic oxazolones (munchnones) 297 can be generated by cyclodehydration of N-substituted a-amino acids 295 or by alkylation of oxazolones 296 (Scheme 7.98). These compounds are reactive and versatile 1,3-dipoles that undergo cycloaddition reactions with dipolarophiles to generate a variety of heterocyclic systems. In particular, this is an extremely versatile methodology to prepare pyrroles that result from elimination of carbon dioxide from the initial cycloadduct. Numerous examples have appeared in the literature in recent years and several have been selected for discussion. The reader should consult Part A, Chapter 4 for an extensive discussion and additional examples. [Pg.195]

Munchnones 298 obtained in situ by N-alkylation of 5(4/f)-oxazolones undergo 1,3-dipolar cycloaddition with dimethyl acetylenedicarboxylate to give Al-alkylpyr-roles 299. 1,3-Dipolar cycloaddition of munchnones with triphenylvinylphos-phonium bromides affords tri- and tetrasubstituted pyrroles 300. In this case, the interaction of the phosphonium group with the carbonyl group leads to high levels of regioselectivity (Scheme 7.99 Table 7.27, Fig. 7.29). ... [Pg.196]

Finally, reaction of 2,4-diphenyl-5(4//)-oxazolone 322 with 4-phenyl-A -tosyl-1-azabuta-1,3-diene was found to be highly dependent on the experimental conditions. At room temperature the sole product was 323 that arises from alkylation of 322 by addition at the imine carbon. However, heating 322 and 4-phenyl-A-tosyl-1-azabuta-1,3-diene gave rise to several products including a 2-pyridone 324, 2,3,6-triphenylpyridine 325, and the pentasubstituted pyrroles 326 and 327. The authors postulated two different reaction mechanisms. Here, both a 1,3-dipolar cycloaddition of the oxazolone and a nucleophilic addition of the oxazolone are possible and that may account for the formation of 324—327. The marked differences in reactivity of 4-phenyl-A-tosyl-l-azabuta-l,3-diene relative to A-alkyl- or A-aryl-1-aza-1,3-dienes was attributed to the powerful electron-withdrawing nature of the tosyl group (Scheme 7.107). ... [Pg.201]

Besides alkyl and aryl oxazolones and their salts, also 5-aminooxazoles 149 [63] as well as the amides of aminooxazoles 151 [64] were used to synthesize trifluoro-methylated pyrroles by cycloaddition. This is not surprising taking into account (hat the aminooxazoles 149 and amides 151 are formal tautomers of the oxazolone imines. Accordingly, a number of CFj-pyrroles 150 and 152 bearing electron-withdrawing groups at the 4-position have been prepared by this method. [Pg.72]

Mesoionic oxazolones 154, prepared from 153, allowed the synthesis of 3-CF3-pyrroles. Thus, their reactions with fluorinated derivatives of ethyl propiolate 155 led to the alkyl pyrrole-3-carboxylates 156 [65]. Similarly, the reaction of compound 157 with hexafluorobut-2-yne gave the pyrrole 158 [66]. [Pg.72]


See other pages where Pyrroles 4-alkyl oxazolones is mentioned: [Pg.115]    [Pg.115]    [Pg.70]   
See also in sourсe #XX -- [ Pg.143 ]




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