They are very interesting in wide area of chemical industries due to their supperior advantages. Solid acids as heterogeneous catalyst can be easily isolated from the reaction process and minimize the corrosion problems .
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In continuation of our interests on the application of the efficient catalyst in synthesis of the organic reactions particularly in heterocyclic chemistry and name reaction synthesis , we wish to review of the BSA solid acid catalyzed reaction in the light of our previous reports. In spite of versatile promoted BSA designed up to now, we hope this report to encourage the invention of other new catalysts based on boron sulfonic acid. BSA as a novel solid acid catalyst with dual Lewis-Bronsted acidic sites was firstly offered for a regioselective reaction at benign condition by Kiasat et al.
Scheme 1 . Boron sulfonic acid or boric trisulfuric anhydride B HSO 4 3 is a trifunctional inorganic catalyst which has strong acidity and good solubility in water and other polar solvents. BSA as a distinguished and heterogeneous catalyst has been utilized in many organic reactions. In the following parts review the details of the application of the boron sulfonic acid for functional group transformation.
Preparation of 1,1-diacetates is a type of carbonyl protection which is applicable as a main step in many organic reactions. Typical studies on condensation of aldehyde 4 and acetic anhydride 5 demonstrate via various heterogenous catalysts [11,12]. We synthesized 1,1-diacetate 6 derivatives by Silica-supported Boron Sulfonic Acid SBSA as an efficient catalyst under solvent-free conditions at room temperature in high yields .
Scheme 2. Carbonyl protection by using BSA. Acylals or 1,1-diacetates, as aldehyde protecting groups, are useful synthon in organic synthesis. However, the reaction of aldehyde 7 and acetic anhydride 5 in the presence of cheap and green solid acid BSA was accomplished under solvent-free conditions at room temperature by Mirjalili et al. Scheme 3 [ 14 ]. Scheme 3. Reaction of 3-nitrobenzaldehyde to acylal. Another important protection in organic strategies specially in multistep reactions is amine protection in which the N -tert-butoxycarbonyl N -Boc group due to some advantages is commonly used .
Herein, an efficient and time-consuming protocol was carried out by Hamadi et al.
The importance of N -formylation reactions have been obscured in the synthesis of pharmaceutically organic compounds containing the cores such as fluoroquinolones, imidazoles, 1,2-dihydroquinolines, formamidines and isocyanides . Recently Hamadi et al. Acylation of alcohols and phenols are the important methods for protection of hydroxyl group, providing a powerful tool in different areas of synthesis, which are often performed in acid catalyzed conditions and are finally removed easily [29,30]. Sedighinia et al. The esters 13 were prepared at short times and in good to high yields Scheme 6 .
Also, Hamadi et al. Scheme 7. The high transformation ability of thiocyanates to other functional groups including, sulfides, aryl nitriles, thiocarbamates, and thionitriles converted them to the benefit synthon . Scheme 8 .
Journal of Chemical Reviews
Scheme 8. Regioselective thiocyanation of epoxides by using BSA. In the light of our studies, the thiocyanation of aromatic and heteroaromatic compounds is proceeded in water using catalytic activity of BSA. This green protocol carried out in the benign conditions with high yields Scheme 9 .
According to the recent research studies, no other type of reaction can provide such large accommodation in synthetic chemistry as much as carbon-carbon bond formation reactions. Synthesis of bisindoles by Friedel-Crafts reaction between indoles and carbonyl compounds can occure in the presence of acid or base .
Hence, Mosslemin et al. Scheme Synthesis of bisindoles and bisbenzotriazoles via BSA catalyst. Madje et al. Friedel-Crafts reaction to anthraquinones synthesis in presence of BSA. Some of biscoumarins derivatives are successful urease and HIV inhibitors [44, 45]. BSA catalyzed preparation of biscoumarins derivatives. A reliable approach for the C—N bond formation is reductive amination which can be provided for primary, secondary and tertiary amines without over-alkylation problems in comparison to direct alkylation of amines with alkyl halides .
On the basis of recent studies, an efficient protocol for the direct reductive amination of aromatic and aliphatic aldehydes or ketones 34 has been accomplished in the presence of sodium borohydride accompanied with the catalytic activity of SBSA in acetonitrile under solvent-free conditions . Reductive amination of aldehydes or ketones to synthesis of amines.
Bisamides containing two C-N bonds are significant targets in the synthetic methodologies of pharmacologically active compounds such as pseudopeptides [51, 52]. Enaminones and enamino esters which often observed in alkaloids and pharmaceuticals are useful precursor in organic synthesis . Quinoxalines are interesting heterocycles in pharmaceutical chemistry which demonstrate biological activities . In continuation of our work, BSA successfully applied for green quinoxalines synthesis.
A green method for conversion of 1,2-phenylendiamine 41 and 1,2-dicabonyl 42 to quinoxaline 43 in aqueous media in the presence of catalytic amount of BSA was achieved Scheme 16 . Quinoline is a main core for organic chemists with owning broad vast biological activities such as anti-inflammatory, antimalarial, antihypertensive, and antibacterial agents properties [64, 65].
Scheme 17 . Preparation of Quinoline compounds via BSA catalyst. There are many consideration of the 2,3-dihydroquinazolin-4 1 H -ones synthesis due to the biological and pharmacological properties including, anticancer, antiinflammatory, and anticonvulsant activities . The convenient conversion of the aldehydes or ketones 34 , isatoic anhydride 47 , and ammonium salts 48 in the presence of tris- hydrogensulfato boron leading to corresponding 2,3-dihydroquinazolin-4 1 H -ones 49 in high yields under solvent-free conditions .
Tree-component synthesis of 2,3-dihydroquinazolin-4 1H -ones. Benzodiazepine framework with various biological activities is main structural motif in medicinal chemistry . Therefore developing methods of benzodiazepine synthesis is important in heterocyclic synthesis. We found that boron sulfonic acid is a useful catalyst for 1,5-benzodiazepines 50 synthesis at room tempreture as illustrated in Scheme 19 .
Benzimidazole which exhibit anti-HIV, anti-virus, anti-tumor and inhibitor properties  is a valuable heterocycle. So, we reported a BSA catalyzed reaction of 1,2-phenylendiamine 41 and aldehydes 4 to prepare benzimidazole 51 derivatives in water at room temperature and with high yields Scheme 20 . Substituted coumarins as significant building block of pharmaceuticals have many biological activities. They are also originated from naturally occurring compounds. The Pechmann reaction is commonly used to synthesis of coumarin analogues .
As illustrated in Scheme 21, this synthetic strategy was occurred in mild and solvent-free conditions .
Using carbon dioxide as a building block in organic synthesis
Preparation of coumarins by using BSA catalyzed Pechmann condensation. Another efficient method for coumarin synthesis is including the interaction of resorcinol 54 and ethyl acetoacetate 55 by Pechmann condensation using catalytic activity of BSA Scheme 22 . Farahi and co-workers successfully reported a novel magnetically heterogeneous catalyst by promotion of boron sulfonic acid with Fe 3 O 4 SiO 2 nanoparticles. The tetrazole groups with widespread applications which can be used as carboxylic acids substitutes play an important role in medicinal chemistry .
Hence, various methodologies in synthesis of tetrazoles are investigated in recent years . We prepare a synthetic reaction for renovation of arylamines 9 , triethyl orthoformate 61 , and sodium azide 62 to aryltetrazoles 64 using boron sulfonic acid in ethylenglicol at high temperature Scheme 24 .
Martinez de Marigorta and I. Chem Commun. Google Scholar. Shimada, M. Ito, K.
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