Alkynylazulenes as Building Blocks for Highly Unsaturated Scaffolds

Recently developed routes to the synthesis of mono- and polyethynylated azulenes and their transformations into linear oligoazulenes with ethynyl and butadiynyl bridges as well as azulenyl-substituted benzenes, cyclobutadiene complexes, and azulene-substituted tetracyanobutadienes are reviewed. The utility of ethynylazulene derivatives for the synthesis of azulene-substituted heterocycles has also been reviewed.