Alumina Sulfuric Acid as an Efficient and Recyclable Heterogeneous Catalyst for the O-Silylation of Alcohols, Phenols, and Oximes

Easy Access to Coumarin Derivatives Using Alumina Sulfuric Acid as an Efficient and Reusable Catalyst under Solvent‐Free Conditions

“…In continuation of our studies on developing cheap and environmentally benign methodologies for organic reactions especially solvent-free conditions and using solid acids as a heterogeneous and reusable catalyst we have decided to use alumina sulfuric acid (ASA) as catalyst in Pechmann reaction [28][29][30][31], to the best of our knowledge, ASA has not yet been used for these types of condensations in solvent-free conditions (Scheme 1).…”

Selective Silylation of Alcohols, Phenols and Oximes Using N‐Chlorosaccharin as an Efficient Catalyst under Mild and Solvent‐Free Conditions

“…Oximes were prepared from aldehydes and ketones according to the literature. 15 All the products are known compounds [4][5][6][7][8][9][10][11][12][13]…”

“…3 A variety of catalysts have been reported for the activation of HMDS such as iodine, 4 trichloroisocyanuric acid, 5 1,3-dibromo-5,5-dimethylhydantoin, 6 sulfonic acid-functionalized nanoporous silica, 7 V(HSO 4 ) 3 , 8 Fe(HSO 4 ) 3 , 9 saccharin sulfonic acid, 10 boric acid, 11 H-b zeolite, 12 alumina sulfuric acid. 13 Although various methods have been reported for the O-silylation of alcohols, phenols or oximes, many of these contain some disadvantages such as long reaction times, operation at high temperature or in acidic conditions, use of solvent, unsuitability for the protection of phenolic OH group or tertiary alcohols, the use of large amounts of catalyst or HMDS, the use of unavailable catalyst, a lack of providing selectivity or at least, the ambiguous selectivity of the method. Thus, there is a need to develop new methods that are more convenient for this important synthetic transformation.…”

Recent advances in catalytic silylation of hydroxyl‐bearing compounds: A green technique for protection of alcohols using Si–O bond formations

“…Shaterian and coworkers developed ortho-silylation of different alcohols, phenols, and oximes by HMDS in the presence of alumina sulfuric acid (ASA) as a heterogeneous and reusable solid acids catalyst at r.t. affording high yields of the products (Scheme 42). [157] When the secondary and tertiary alcohols were present, one can witness a selective conversion of the primary alcohols into their corresponding ortho-silylated products. In this sense, authors comparatively performed this reaction with different catalysts, that is, lithium perchlorate, iodine, and cupric sulfate pentahydrate.…”