HClO4–SiO2 as a novel and recyclable catalyst for the synthesis of bis-indolylmethanes and bis-indolylglycoconjugates

An eco-friendly procedure for the efficient synthesis of bis(indolyl)methanes in aqueous media

“…Even when the desired reactions proceed, more than stoichiometric amounts of Lewis acids are required. Many attempts have been done by organic chemists to circumvent this problem [17][18][19][20][21][22]. However, most of the reported methods suffer from one or more of the following drawbacks: using large amounts of solid supports or un-recyclable catalysts which would eventually result in the generation of a large amount of toxic waste, long reaction times, moderate yields of the products, amenable only for aldehydes as carbonyl compounds and requiring an additional microwave or ultrasound irradiation.…”

Silica supported perchloric acid (HClO4-SiO2): A mild, reusable and highly efficient heterogeneous catalyst for the synthesis of 14-aryl or alkyl-14-H-dibenzo[a,j]xanthenes

“…HClO 4 -SiO 2 catalyzed synthesis of 14-aryl or alkyl-14-H-dibenzo[a,j] xanthenes. [35], Synthesis of bis-indolylmethanes [36], glycosylation of sugars [37] and N-tert-butoxycarbonylation of amines [38], synthesis of tetrasubstituted imidazoles [39] and synthesis of poly-substituted quinolines [40].…”

Silica‐supported perchloric acid as a recyclable catalyst for efficient trimethylsilyl cyanide addition to aldehydes

“…Because of their larger surface area, they provide better selectivity, higher activities and better mechanical and thermal stabilities, and can easily be recovered from reaction mixtures and reused. As found recently, silicasupported perchloric acid has emerged as a poweful catalyst for various organic transformations, including synthesis of bisindolylmethanes and bis-indolylglycoconjugates, [15] synthesis of 1,4-dihydropyridines, [16] synthesis of acylals from aldehydes, [17] transformation of thioglycosides to their corresponding 1-Oacetates, [18] 1,3-dithiolane/dithiane formation, [19] tetrahydropyranylation, oxathioacetalization and thioacetalization, [20] synthesis of coumarins via Pechmann condensation, [21] N-tertbutoxycarbonylation of amines, [22] selective removal of anomeric O-acetate groups in carbohydrates, [23] cleavage of benzylidene acetals, [24] glycosylation using sugar trichloroacetimidates as glycosyl donors, [25] selective deprotection of terminal isopropylidene acetals and trityl ethers, [26] Ferrier rearrangement of glycals, [27] acetal/ketal formation [28] and chemoselective carbon-sulfur bond formation. [29] Herein we report our findings on the Winkler reaction using HClO 4 -SiO 2 (0.6 mol%) to act as a highly effective catalyst.…”