Salts 7-azaindolium

Takenaka and coworkers used 2-aminopyridinium salts as dual hydrogen-bond donors for the activation of nitroalkenes. The 7-azaindolium salt 65 was found to be particularly effective for the Friedel-Crafts reaction of nitroalkenes with various electron-rich arenes as well as for intra- and intermolecular Diels-Alder reactions (Scheme 10.63) [163, 164]. The same concept was successfully applied to the enantioselective conjugate addition of 4,7-dihydroindoles to nitroalkenes using helical chiral 2-aminopyridinium salts (Scheme 10.64) [165]. The reaction was found to have a broad substrate scope, affording various 2-substituted indoles in good to high enantiomeric ratios. 

Methyl-7-azaindolium iodide (111, X = I) was also prepared by Saxena in addition to the 7-benzyl and 7-p-nitrobenzyl salts. These all gave anhydro bases (e.g. 112). 

---