Indoles indium triflate

Reactions with otP-Unsaturated Ketones, Nitriles and Nitro-Compomds Such reactions are usually effected using acid (see below), or one of a number of mild Lewis acids, such as scandium iodide (with microwave heating), indium bromide " or hafnium triflate, and can be looked on as an extension of the reactions discussed in 20.1.1.6. In the simplest situation, indole reacts with methyl vinyl ketone in a conjugate fashion in acetic acid/acetic anhydride. ... 

The iminium ion electrophile can also be prepared separately, as a crystalline solid known as Eschen-moser s salt (Me2N =CH21 ) and, with this, the reaction is normally carried ont in a non-polar solvent. Examples that illnstrate the variation in iminium ion structure that can be tolerated include the reaction of indole with quinolines, catalysed by indium(lll) chloride, with benzylidene derivatives of arylamines, catalysed by lanthanide triflates, with ethyl glyoxylate imines " (no catalyst required) and with dihydro-1,4-oxazin-2-ones. °" ... 

A series of peracetylated Cl-deoxyalditol and C-glycoside dipyrranes were prepared from the corresponding dithioacetal derivatives yields of the pyrrole condensation were reported to be up to 62% (13TL1137). En route to a synthesis of the marineosins, Lindsley utilized a late-stage incorporation of the pyrrole moiety by the nucleophilic displacement of an iminium triflate salt (13TL2231) a related approach was disclosed by Shi et al. (130BC2936). Konduru and Ahmed used pyrrole and indole to open chal-cone epoxides with catalytic amoimts of indium (111) chloride (13SC2008). 

Nagarajan and Perumal have demonstrated that indium(III) triflate also promotes the acylation of indoles under mild conditions and with short reaction times. Indium(III) triflate also catalyzes the reaction of indole with substituted henzaldehydes to afford his-indolyhnethanes (eq 4). 

Other Applications. Indium(III) triflate catalyzes the intramolecular Diels-Alder reaction of furans in aqueous media under microwave irradiation. In a one-pot procedure, allyl bromide reacts with (2-furfuryl)anilines affording the intramolecular Diels-Alder products in good to excellent yields, in very short reaction times (eq 19). Under thermal conditions, yields of40-45% are obtained. Such products allow access to indole derivatives through cleavage of the epoxy bridge and aromatization. 

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