Synthesis and Some Reactions of 2-Amino-1-azaazulene-3-carbaldehyde

2-Chloro-1-azaazulene-3-carbaldehyde (1a) reacted with pyridine, followed by a reacion with piperidine to give 2-amino-1-azaazulene-3-carbaldehyde (1b) in excellent yield. Compound 1b was also obtained by a Vilsmeier–Haack reaction of 2-amino-1-azaazulene. Acetylation of 1b yielded a 2-acetylamino derivative, whereas methylation gave a 1-methylated compound. Reactions of 1b with hydrazines and alkylamines gave the corresponding hydrazones and Schiff bases, respectively, in excellent yields. The reactions of 1b with active methylene compounds gave 1,10-diazabenz[a]azulen-2(1H)-one derivatives. The reaction of 1b with guanidine gave pyrimidine-fuzed 1-azaazulene.