Silica sulfuric acid: a reusable solid catalyst for one pot synthesis of densely substituted pyrrole-fused isocoumarins under solvent-free conditions

Abstract

SummaryA convenient and efficient methodology for the synthesis of densely substituted pyrrole-fused isocoumarins, which employs solid-supported silica sulfuric acid (SSA) as catalyst, has been developed. When the mixture of ninhydrin adducts of acetylacetone/ethyl acetoacetate and primary amines was heated on the solid surface of SSA under solvent-free conditions, the pyrrole-fused isocoumarins were formed in good yields. This synthetic method has several advantages such as the employment of solvent-free reaction conditions without the use of any toxic reagents and metal catalysts, the ease of product isolation, the use of a recyclable catalyst, the low cost, the easy availability of the starting materials, and the excellent yields of products.

An Expedient Catalytic Process to Obtain Solketal from Biobased Glycerol

“…Silica sulfuric acid (H 2 SO 4 •SiO 2 or SSA, also known as sulfuric acid adsorbed on silica) is a well-known solid acid catalyst with various applications in organic chemistry [26]. It can be obtained by mixing aqueous sulfuric acid with regular chromatography silica gel, followed by water removal at 130 • C (hereafter referred as "wet" SSA or simply SSA) [27][28][29], or by dropping chlorosulfonic acid directly on dry silica (referred as "dry" SSA") [30][31][32]. Its features like low cost, availability, low toxicity, and easy separation from the reaction media spurred us to study the application of the two popular SSA variants (typical loading 2.63 mmol -SO 3 H/g) in the said acetalization process (Figure 2).…”

“…In the attempt to compare alternative Brønsted species, orthophosphoric acid was first considered but, when supported on silica (H 3 PO 4 •SiO 2 , 3.0 mmol/g) it gave a disappointing result on acetalization of glycerol (27% isolated yield), suggesting the importance of the acid strength [4]. At this point, finding other candidates seemed not straightforward as monoprotic donors were expected to be devoid of catalytic activity, accordingly to the popular SSA representation based on sulfuric acid esters with surface silanols [22][23][24][25][27][28][29][30][31][32].…”

1,3-Diketones. Synthesis and properties

“…Fused heterocyclic systems 222 containing polysubstituted pyrrole and isocoumarin fragments were synthesized by one-pot reaction of acetylacetone first with ninhydrin and then with primary amines under solvent-free conditions using silica sulfuric acid (SSA) as catalyst [152]. The proposed mechanism is shown in Scheme 143.…”

Synthesis and Biological Evaluation of Novel 1‐(4‐(Hydroxy(1‐oxo‐1,3‐dihydro‐2H‐inden‐2‐ylidene)methyl)phenyl)‐3‐phenylurea Derivatives

“…High reactivity of 1,3‐diketones allow molecular diversity in the synthesis of organic and natural compounds. For example, pyrazoles, [ ][ ] pyrroles, [ ][ ] pyrimidines, [ ][ ] furans, [ ][ ] chromenes, xanthenes, [ ][ ] isocoumarins, [ ][ ] pyranones and sulfur‐containing heterocycles can be synthesized from the 1,3‐diketones. In the literature, 1,3‐diketones have been reported as having potential uses as catalyst, anticancer I, antibacterial II, antifungal, antioxidant III ( Fig.…”