N-Bromosuccinimide (NBS) as Promoter for Acylation of Sydnones in the Presence Acetic Anhydride under Neutral Conditions

Abstract

Various 4 -acetyl sydnones (2) can be prepared by reaction of the corresponding 3-aryl sydnones (1) with acetic anhydride at ~110 o C promoted by N-Bromosuccinimide (NBS) as an effective reagent for acylation of sydnones under neutral conditions in satisfactory yields. Sydnones (1) are archetypal members of the class of compounds known as mesoionic which were first prepared by Earl and his co-workers in 1935. 1They undergo a variety of transformations including electrophilic aromatic substitution (at the 4-position), 2 cleavage with HCl to form hydrazines, 3 or heterocycles 4 and 1,3 -dipolar cycloadditions to form pyrazoles or related species. 5 Perhaps the biological activity: inter alia sydnone; have been used efficaciously as antibacterial, 6 antitumor, 7 antimalarial, 8 anti-inflammatory, 9 and antihyhypertensive agents. 10 Their activity as MAO (monoamine oxidase) inhibitors has also been reported. 11 Acylation occurs, with various acylation mixtures and with a large variety of 3-aryl substituents, exclusively at the sydnone 4-position. 12-16 It had been reported 17 that it was not possible to acetyl-3-arylsydnone with either acetic anhydride or benzoyl chloride in the presence of a lewis acid catalyst and Friedel-Craftes conditions to obtain the 4-acetylsydnone because the difficulties stem from the fact that using the standard Friedel-Craftes conditions (acid chloride/aluminum chloride) the sydnones do not react, presumably due to coordination of the lewis acid with the exocyclic oxygen atom in the sydnone. 18 Successful acylation has relied on the use of alkyl anhydrides and acids such as perchloric, 19 phosphoric 20 or boron trifluoride or alkyl carboxylicacids and phosphorus pentoxide. 21 More recently, Montmorillonite K-10 22 and HClO 4 under high powered ultrasonic bath 23 have been reported as efficient catalysts for acylation of 3-substituted sydnones in the presence acetic anhydride.

1,3-Dibromo 5,5-dimethylhydantoin (DBH): A novel and efficient catalyst for the synthesis of 14-aryl-14H-dibenzo[a, j] xanthenes under solvent-free conditions

“…In continuation of our on-going research on various transformations by halogenating agents [26][27][28][29][30][31][32], herein we reported the use of DBH as a more robust and efficient catalyst for the one-pot synthesis of the aryl-14H-dibenzo[a,j] xanthenes derivatives 3a-o by reaction of -naphthol with different aromatic aldehydes in excellent yields (90%-96%) under solvent free conditions (Scheme 1, Table 1). As shown Scheme 1 a) All the isolated products were characterized by their physical properties, by 1 H and 13 C NMR and IR spectra, and by direct comparison with literature data ( [14][15][16], [22][23][24][25]).…”

Fe3O4@SiO2@Im‐bisethylFc [HC2O4] as a novel recyclable heterogeneous nanocatalyst for synthesis of bis‐coumarin derivatives

“…We also synthesized a series of aromatic aldehydes (Scheme ), and applied them to synthesize new bis‐coumarin derivatives using condensation of these aldehydes and 4‐hydroxycoumarin catalyzed by Fe 3 O 4 @SiO 2 @Im‐bisethylFc [HC 2 O 4 ] nanocatalyst under optimized conditions (Table ) .…”

“…and terephthaldehyde (1 equiv. ), 3,3′‐[(4‐formylphenyl)methylene]bis(4‐hydroxy‐2 H ‐chromen‐2‐one) ( 3o ) was obtained in 71% yield. By controlling the molar ratio of 4‐hydroxycoumarin (4 equiv.)…”

“…These derivatives have been found useful in an extensive range of biological and pharmaceutical actions, including enzyme inhibitors, anticoagulants, antioxidants, antitumor drugs, anti‐diabetic (α‐glucosidase inhibitors) urease inhibitors, anticancers, antibacterials, inhibit c‐Met phosphorylation in BaF 3 /TPR‐Met and EBC‐1 NSCLC cell lines, antimicrobial, antiviral, proliferation inhibition of K‐562 and inhibit HIV‐1 . Recently, several methods have been reported for the synthesis of bis‐coumarin by the reaction of 4‐hydroxycoumarin and various aldehydes in the presence of various homogeneous and heterogeneous catalysts and under various reaction conditions, such as tetrabutylammonium bromide (TBAB), molecular iodine, [bmin] BF 4 , SO 3 H‐functionalized IL, sodium dodecyl sulfate, piperidine, n‐dodecylbenzene sulfonic acid (DBSA), [pyridin‐SO 3 H]Cl, TrBr and [Fe 3 O 4 @SiO 2 @(CH 2 ) 3 ‐Im‐SO 3 H]Cl, MNPs‐PSA and Fe 3 O 4 @SiO 2 @(CH 2 ) 3 semicarbazide‐SO 3 H/HCl . Although all the procedures for the synthesis of corresponding bis‐coumarin have their merits, the main disadvantages of these methods are often tedious work‐up procedures, low yields, harsh reaction conditions, and the use of toxic, corrosive and expensive catalysts, and the recovery of these catalysts are often difficult.…”

1,3‐Dibromo 5,5‐dimethylhydantoin (DBH)‐Catalyzed Solvent‐Free Synthesis of 2‐arylbenzimidazoles under Microwave Irradiation

“…In continuation with the search for simple non-hazardous methods for the transformations in organic synthesis using halogenating agents [18][19][20][21][22][23][24][25][26] , herein we report a highly versatile and efficient synthesis of 2-aryl-benzimidazoles 3 from o-phenylenediamine, aldehyde and catalytic amounts of 1,3-dibromo 5,5-dimethyl hydantoin (DBH) under solvent-free and microwave conditions in high yields (Scheme 1).…”