Synthesis of N-substituted 1H-indeno[2,1-b]pyridines

It was established that N-phenacyl and p-nitrophenacyl bromides and N-methyl-1-azafluorenium iodide, as well as N-phenacyl-7-nitro-1-azafluorenium bromide, are converted to N-substituted 1H-indeno[2,1-b]pyridines rather than to the corresponding yilds or indenoindolizines upon treatment with bases under various conditions. All of the pseudoazulenes of this type were isolated in the form of crystalline black or dark-violet substances. In contrast to pseudoazulenes of the 1H-indeno[1,2-b]-and 2H-indeno[2,1-c]pyridine series, they are stable both in the solid state and in solutions. 1H-1-Methylindeno[2,1-b]pyridine forms a perchlorate and a picrate (retention of the pseudoazulene structure) but is converted to N-methyl-1-azafluorenium chloride by the action of hydrogen chloride. Spectral characteristics are presented for all of the compounds obtained. © 1980 Plenum Publishing Corporation.