Nitrations indium triflate

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. 

The nitration of arenes is traditionally promoted by stoichiometric amounts of concentrated sulfuric acid. In a mild alternative, indium(III) triflate proves to be an efficient nitration catalyst for a range of aromatics, replacing concentrated H2SO4. Under biphasic conditions, bromobenzene is nitrated to afford a 2 1 mixture of para and ortho products in high isolated yield (eq 8). 

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