Lewis acid catalysts indium triflate

Aminoalkyl and Related Acids. - Further development of the classical three component approach to aminoalkylphosphonates (the Kabachnik-Fields reaction) has been reported. The reaction of aldehydes, hydroxylamines and dimethyltrimethylsilyl phosphite using lithium perchlorate/diethyl ether as a catalyst gives N-trimethylsilyloxy-a-aminophosphonate derivatives. The catalytic activities of various lanthanide triflates as well as indium trichloride have been examined for the Kabachnik-Fields type reactions of aldehydes, amines and the phosphorus nucleophiles HP(0)(0Et)2 and P(OEt)3 in ionic liquids. TaCb-Si02 has been utilized as an efficient Lewis acid catalyst for the coupling of carbonyl compounds, aromatic amines and diethyl phosphite to produce a-... 

To improve the yields and therefore the scope of this aqueous aldolization, the use of lanthanide triflates as water-tolerant Lewis acids was recommended [9, 60]. After completion of the reaction nearly 100% of the catalyst is recovered from the aqueous layer and can be re-used quite easily. Other water-tolerant Lewis acids, including indium chloride [61] and tris(pentafluorophenyl) boron [62], were proposed as catalysts in the aqueous aldol reaction. 

Taking into account the competitive hydrolysis of the silyl enol ether, this reaction is remarkable. The method was shown to be general and was extended to a variety of aldehydes and several a,j9-unsaturated carbonyl compounds giving uniformly 1,4-addition with aldehydes and a mixture of 1,4- and 1,2-adducts in the case of ketones [187]. Later, this aqueous version of the Mukaiya-ma reaction was shown to give near quantitative yields in the presence of a water-tolerant Lewis acid such as ytterbium triflate [188]. Keeping with the same concept,copper(II) triflate [189],indium(III) trichloride [190],tris(pentafluoro-phenyl)boron [191] and scandium(III) triflate in the presence of a surfactant [192] have proved to be active catalysts. 

Additives that can be added to aqueous reactions include Lewis acids, which have roles as catalysts in organic transformations, mainly in Diels-Alder reactions [24]. A number of Lewis acids which can be used in water have been described, such as nitrates, for example, Cu(N03)2 and Zn2 +, Ni2 +, Co2+ analogs [25], lanthanide triflates, Ln(OTf)3 [26], and others, including indium trichloride [27]. Increased yields and product selectivities have been observed in several systems. A typical example is the three-component hetero-Diels-Alder reaction catalyzed by lanthanide triflate (Equation 4.14). Lanthanide triflates were used in the pH range 5-7, and when no Ln (OTf)3 was added, the product was isolated in only 4% yield however, with added lanthanide catalyst the yield was increased to 64% [28]. 

A recent improvement in the rate of the aqueous Diels-Alder reaction came with the use of Lewis acid in aqueous media. The first study deals with the Diels-Alder reaction between cydopentadiene and a bidentate dienophile. A large acceleration can be achieved by the combined use of copper(II) nitrate as a catalyst and water as a solvent [10, 34], Lanthanide and scandium triflates [9, 35] as well as indium trichloride [36] were found to catalyze the Diels-Alder reaction in water. 

There has been a review of asymmetric Friedel—Crafts reactions. It has been shown that the rhodium-catalysed reaction of potassium phenyltrifluoroborate with A-tosyl ketimines may lead to products such as (18) with high enantioselectivity. (g) The reaction of A-t-butanesuUinylimino esters with arenes to give products (19) is catalysed by Lewis acids, such as indium triflate, and may lead to enantio-metrically enriched a-glycines. The intramolecular alkylation of hydrogenated 0 tetralins, shown in Scheme 2, using iron(III) or aluminium(III) catalysts yields cis-hexahydrobenzophenanthridines. Formation of a stabilized carbocation intermediate is... 

The authors tested InCl3 and Sc(OTf)j as Lewis acids to catalyze the domino process. Scandium(III) triflate mostly gave a 1 1 mixture of cis- and trans-64, while indium(III) chloride was able to provide mostly a 1 2.3 ratio. The yields showed to be higher with InCl3. The reaction could also be conducted without any catalyst, but the yields were considerably lower (65-70%, cisltrans= 1 1). 

The aza-Diels-Alder reaction of imines with diene of Danishefsky is an important route to 2,3-dihydro-4-pyridones. A number of Lewis acids have been used to catalyze the reaction in organic solvents. In water the reaction was realized by acid catalysis via iminium salts or by Bronsted acids. The montmorillonite K-10 catalyzed this cycloaddition in water or in aqueous acetonitrile in excellent yield. Recently Kobayashi has performed the reaction in water at room temperature under neutral conditions in two (imine - - diene) or three (aldehyde -b amine -b diene) component versions by using sodium triflate as catalyst. Imine intermediates from the indium-mediated reaction, in aqueous medium at 50° C, between aromatic nitro compounds and 2,3-dihydrofuran undergo aza-Diels-Alder cycloadditions to give tetrahydroquinoline derivatives in good overall yields. ... 

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