Nitration of sydnones. Reaction with 3‐Arylsydnones containing electron‐donors on the aryl ring

Abstract

Exclusive aryl ring nitration of a series of 3‐arylsydnones 1 with electron donors (di‐ or tri‐methyl) on the aryl ring is reported.

Oxadiazoles

“…With 4-unsubstituted 3-alkyl-or 3-phenylsydnones, substitution occurs only at the electron-rich C4, while when aryl substituents are present at C3 the position of the electrophilic attack depends upon the nature of the aryl group, Exclusive aryl ring nitration occurs with electron donors on the aryl group [84]. Thus, 3-(2-aminophenyl) sydnone is brominated in the benzene ring para to the amino group [85] while the nitration of 3,4-diphenylsydnone affords the 4-nitrophenyl derivative.…”

1,3‐Dibromo‐5,5‐dimethylhydantoin (DBH) as an efficient promoter for acetylation of 3‐arylsydnones in the presence of acetic anhydride under neutral conditions

“…This can be accounted for by the deactivation of the aryl substituent due to the electron-withdrawing effect of the sydnone ring N-3 position that bears a substantial fractional positive charge [12,13]. Acylation of sydnones, among other aromatic substitution reactions, is of considerable interest in organic synthesis that has been implemented by various reagents exclusively at the sydnone 4-positions as already mentioned [14][15][16].…”

Catalytic Activity of 1,3-Dibromo-5,5-dimethylhydantoin (DBH) in the One-Pot Transformation ofN-Arylglycines toN-Arylsydnones in the Presence of NaNO2/Ac2O under Neutral Conditions: Subsequent Bromination of these Sydnones to their 4-Bromo Derivatives

“…This is probably attributable to deactivation of the aryl substituent by the electron-withdrawing effect of the sydnone ring N-3 position that bears a substantial fractional positive charge. 11,12 Sydnones are intrinsically neutral substances that are normally prepared by dehydrative cyclization of N-nitrosamino acids. 13 N-Nitrosamino acids used in the synthesis of sydnones are themselves prepared from N-nitrosation of amino acids.…”