Sulfuric Acid Adsorbed on Silica Gel. A Multipurpose Acid Catalyst

Chavez, Flavio; Suárez, Silvia; Díaz, Miguel

doi:10.1080/00397919408019058

Cited by 35 publications

(13 citation statements)

References 16 publications

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“…The aminal4 turned out to be a single diastereoisomer proven by 'H-NMR NOE measurements. The subsequent rearrangement reaction to 5 was achieved in high yield by heating 4 with various acids such as Montmorillonite K 10 [18], sulfuric acid on silica gel [19], or CF,COOH in toluene. Weak acids such as AcOH did not cause the rearrangement, but led instead to 0-acetylation of 4, whereas strong acids in polar solvents gave undefined mixtures and decomposition products.…”

Section: Resultsmentioning

confidence: 99%

Total synthesis of 2,6‐dimethylergolin‐8α‐amines

Waldvogel

Engeli

Küsters

1997

Helvetica Chimica Acta

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A stereoselective total synthesis of the racemic form of the 2,6-dimethyIergolin-Sx-amine derivative 111, previously obtained semi-synthetically from lysergic acid, is described. Starting from the commercially available tricyclic lactam 1, the 9,lO-didehydroergoline skeleton containing an angular Me group in position 3 (see 18) is built up in several steps applying a Woodward D-ring annelation sequence. The introduction of the 8-amino group is achieved with complete diastereoselectivity to give exclusively the Xa-derivative 22. Subsequently, a WagnerMeerwein-type migration of the angular Me group yields the 2-niethylated 9,10-didehydroergoline derivative 31.The feasibility of this key transformation was tested on the two model systems 4 and 7 prior to the evaluation of the total synthesis. A stereoselective Birch reduction to the rrans-fused ergoline, and deacetylation/acylation conclude the total synthesis of the racemic target compound 34.In addition, the resolution of an early intermediate (see 3) by chromatography on a chiral stationary phase is presented which demonstrates that the described total synthesis could also be used for the preparation of the biologically active (SR,8S,lOR)-enantiomer 111.

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Section: Resultsmentioning

confidence: 99%

Total synthesis of 2,6‐dimethylergolin‐8α‐amines

Waldvogel

Engeli

Küsters

1997

Helvetica Chimica Acta

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“…Table 2, entry 7). Similary aliphatic and cyclic ketones underwent this reaction to give the corresponding amines in excellent yield ( Table 2, entries [14][15][16][17][18][19][20]. However, to examine a greater range of amines to better illustrate the scope and limitation of the method, we have investigated the reaction with both primary and secondary amines, such as allylamine, piperidine, pyrrolidine, and morpholine, using PhCHO as representative aldehyde and cyclohexanone and 2-heptanone as representative ketones ( Table 2, entries [10][11][12][13][14][15][16][17][18][19][20].…”

Section: Methodsmentioning

confidence: 99%

“…[18] Recently, silica-gel-supported sulfuric acid (SSA) has been found to be an efficient catalyst for a variety of acid-catalyzed reactions, such as dehydration of alcohols, preparation of a,b-unsaturated keto enol-ethers, preparation and hydrolysis of 1,3-dioxolanes, and protection of alcohols. [19] Heterogeneous reactions have received attention in recent years because of their greater selectivity and simple reaction workup. [20] In addition, solvent-free conditions are especially suitable for providing an ecofriendly system.…”

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confidence: 99%

Reductive Amination of Aldehydes and Ketones Under Heterogeneous and Solvent-Free Conditions Using Sodium-Borohydride and Silica-Gel–Supported Sulfuric Acid

Alinezhad

Tajbakhsh

Zare

2009

Synthetic Communications

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“…The highest conversion was achieved with Ru/C catalyst using toluene as a solvent, giving, however, allobetulin as the main product (Table , experiment 1). Allobetulin has been previously synthesized by refluxing betulin in dichloromethane in the presence of sulphuric acid on silica or p‐toluenesulphonic acid using montmorillonite KSF, montmorillonite K10, kaolinite or bleaching clay as catalysts . Thus active carbon support in Ru/C contains also some acidic sites, which might be responsible for formation of allobetulin (structure of allobetulin is given in Figure ).…”

Section: Figurementioning

confidence: 99%

Unprecedented Selective Heterogeneously Catalysed “Green” Oxidation of Betulin to Biologically Active Compounds using Synthetic Air and Supported Ru Catalysts

et al. 2016

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Selective oxidation of betulin to biologically active betulinic aldehyde is demonstrated for the first time over Ru/C catalyst mixed with a basic hydrotalcite and using SiO 2 as a dehydrating agent in synthetic air at 108 8C in toluene with conversion of 41 % in 24 h and 67 % selectivity to betulinic aldehyde, whereas without SiO 2 with Ru/C the corresponding conversion and selectivity values were 20 % and 66 %, respectively. Over another, acidic Ru/C catalyst even higher conversion was achieved, giving, however, allobetulin as a main product. These results indicate that basicity and absence of water are crucial for selective botulin oxidation over Ru catalysts. The conversion levels are comparative with the results in the oxidation of hydroxymathylfurfural, which contains a hydroxymethyl group attached to the heterocyclic ring.Pharmaceuticals are conventionally synthesized in multistep procedures using several organic solvents and stoichiometric reagents, therefore the E-factor, i. e. the amount of waste per formed product is very high. [1] Currently there is a high interest to develop more environmentally friendly methods for production of pharmaceuticals, moreover starting the synthesis from naturally occurring compounds. A potential compound for medical applications is betulin, which is present in the bark of some tree species, such as Betula sp. [2,3] Betulinic acid is present in birch bark or cork of cork oak (Quercus suber L.) and can be isolated and extracted, [2] whereas the stem bark of Tectona grandis contains betulinic aldehyde. [4] In this work betulin oxi-dation was investigated using heterogeneous catalysts and air as an oxidant (Figure 1).Oxidation of betulin produces both betulonic and betulinic aldehydes and acids, respectively, as products ( Figure 1). Betulinic acid has been conventionally prepared from betulin in socalled Jones oxidation process using Cr 2 O 3 as an oxidant. The formed betulonic acid can be reduced to betulinic acid with NaBH 4 in tetrahydrofuran. [18] Betulinic acid was also synthesized via oxidation of betulin using Keggin type tungstophosphoric acid together with potassium dichromate between 15-35 8C during 60 to 240 min giving betulonic acid, which is reduced to betulinic acid with NaBH 4 in an organic solvent. [19] TEMPO (2,2,6,6-teramethylpiperidine -oxyl) catalyst has also been used in the oxidation of betulin to betulinic acid with iodine or (diacetoxyiodo)benzene DIB as oxidants. 2 Furthermore, a high isolated yield of betulinic acid (86 %) was achieved, using 4-acetamido-TEMPO as a catalyst together with NaClO 2 /NaOCl at 50 8C. [20] The above-mentioned betulin derivatives exhibit several biological and medicinal properties. [5][6][7][8][9][10][11][12][13][14][15][16][17] Several examples were given from betulin oxidation with homogeneous catalysts, e. g. RuCl 2 (PPh 3 ) 3 and TEMPO as a cocatalyst in oxygen at 1 atm and 105 8C giving 15 % yield of betulinic aldehyde at 17 % conversion in 27 h and in 8 h at 100 8C under 8 bar 69 % of betulinic aldehyde, respectively...

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Sulfuric Acid Adsorbed on Silica Gel. A Multipurpose Acid Catalyst

Cited by 35 publications

References 16 publications

Total synthesis of 2,6‐dimethylergolin‐8α‐amines

Total synthesis of 2,6‐dimethylergolin‐8α‐amines

Reductive Amination of Aldehydes and Ketones Under Heterogeneous and Solvent-Free Conditions Using Sodium-Borohydride and Silica-Gel–Supported Sulfuric Acid

Unprecedented Selective Heterogeneously Catalysed “Green” Oxidation of Betulin to Biologically Active Compounds using Synthetic Air and Supported Ru Catalysts

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