Boric acid as cost-effective and recyclable catalyst for trimethylsilyl protection and deprotection of alcohols and phenols

Abstract

O ácido bórico foi usado neste trabalho como um catalisador "verde", seletivo e reciclável, para a trimetilsililação de álcoois e fenóis usando hexametildissilazano em acetonitrila. A desproteção de trimetilsililéteres para regenerar seus alcoóis e fenóis precursores foi também realizada usando este catalisador em água à temperatura ambiente. As características de destaque desta metodologia são o baixo custo do processo, as condições brandas de acidez, os rendimentos excelentes e a disponibilidade ampla do catalisador.Boric acid has been used as a green, selective and recyclable catalyst for trimethysilylation of alcohols and phenols using hexamethyldisilazane in acetonitrile. Deprotection of trimethylsilyl ethers to their parent alcohols and phenols was also achieved using this catalyst in water at room temperature. The salient features of this methodology are cheap processing, mild acidity conditions, excellent yields of products and easy availability of the catalyst.

Synthesis of dipyrromethanes in aqueous media using boric acid

“…[16][17][18] Our research group has developed a few green methods for synthesis of dipyrromethanes and related compounds [19][20][21][22] in addition to other groups. [23][24][25] Boric acid has been used as catalyst for synthesis of bis(indolyl)methanes, 26 benzoxanthenes, 27 dehydration of glucose, 28 protection and deprotection of alcohols and ethers, 29 Nacylation, 30 bromination, 31 aza Michael reactions, 32 Biginelli reactions 33 and other condensation reactions. [34][35][36] Herein, we have described the use of boric acid as an innocuous and highly efficient catalyst for the condensation reaction of pyrrole and aldehydes in aqueous medium to afford the corresponding dipyrromethanes.…”

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]…”

“…However, the major disadvantage of this reagent is its poor silylating power which demands the use of catalysts and high temperature. 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.…”

Microwave-Assisted Condensation Reactions of Acetophenone Derivatives and Activated Methylene Compounds with Aldehydes Catalyzed by Boric Acid under Solvent-Free Conditions

“…They can indeed act as Lewis acids but also as activators of functional groups such as hydroxyl and carboxylic groups by reversible covalent interactions [2]. Among them, boric acid was found to be an efficient catalyst in numerous reactions such as selective esterification of α-hydroxycarboxylic and malonic acids [3,4,5], amide formation from carboxylic acids [6,7,8], transamidation of carboxamides [9], trimethylsilylation of alcohols and phenols [10], decarboxylation of cyclic β-enaminoketoesters [11], ipso-hydroxylation of aryl boronic acids [12], aza [13] and thia-Michael addition [14], Friedel-Crafts alkylation of indoles [15] as well as in diverse multicomponent reactions [16,17,18,19].…”