Indium triflate salt

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). 

C5Mes)In is with CF3SO3H which gives the triflate salt of In ". The salt ln[02SCF3] is air-sensitive and hygroscopic but is, nonetheless, a convenient source of indium(I) as an alternative to ln(I) halides. 

Scheme 8.6 Reactivity patterns of monovalent indium triflate (a) and halide (b) salts and their crown ether complexes (X = Cl, Br, I R = H, Cl). With permission from Ref [88],...

In 2004 an indium-NHC complex was reported which was prepared from an air stable imidazolium salt precursor.29 Reaction of one equivalent of imidazolium salt with InMe3 affords (NHC)InMe2Cl 18 (Scheme 12). The indium-NHC bond distance of 2.267(2) A is shorter than that of InH3(NHC), though longer than the bis-NHC InBr3(NHC)2. Mono-triflate (19) and bis-triflate (20) complexes can also be prepared by treatment of 18 with trimethyl silyl triflate and treatment of 19 with triflic acid respectively. 

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. °" ... 

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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