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.

The 1,3-dibromo-5,5-dimethylhydantoin (DBH) was found to efficiently catalyze the one-pot synthesis of highly functionalized tetrasubstituted furan derivatives by the reaction of 1,4-diarylbut-2-ene-1,4-diones and acetoacetates in i-PrOH as the solvent at 80 -908 for 3 -7 h. The products were formed in high yields (82 -95%) under mild and neutral conditions.Introduction. -Substituted furan derivatives are important synthetic intermediates [1] and are found as structural units in many natural products such as in kallolides [2], cembrenolides [3], pheromones [4], and polyether antibiotics [5]. These heterocycles have found applications in many pharmaceuticals, fragrances, and dyes [6]. Furan subunits have also been used as building blocks for a large number of heterocyclic compounds and as synthons in natural-product synthesis [7]. As a consequence, the synthesis [8 -11] and the applications [12 -15] of furan derivatives still attract the attention of organic chemists. The most common strategy involved in the synthesis of furans is the cyclization [16] of 1,4-dicarbonyl compounds. Of the various other methods, syntheses involving transition-metal salts have recently been described for the preparation of substituted furan derivatives [17]. Oh and co-workers [18] have synthesized highly substituted furans via Pt-catalyzed hydroxy-or alkoxy-assisted cyclization of 2-(alk-1-yn-1-yl)alk-2-en-1-ones. More recently, Jaisankar and coworkers reported a novel method for the preparation of highly substituted furans by InCl 3 -catalyzed nucleophilic addition followed by a cyclization reaction, although it was limited to specific substrate classes [19].

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An expeditious synthesis of 2-aryl-benzimidazoles by the condensation ofo-phenylenediamine with various arylaldehydes is described. This greener protocol is catalyzed by 1,3-Dibromo 5,5-dimethylhydantoin (DBH), and proceeds efficiently in the absence of any organic solvent under thermal condition and microwave irradiation in high yields.