Polycyclic aromatic hydrocarbons (PAHs) are mostly formed during the incomplete combustion of organic materials, but their importance and presence in materials science, and astrochemistry has also been proven. These carcinogenic persistent organic pollutants are essential in the formation of combustion generated particles as well. Due to their significant impact on the environment and human health, to understand the formation and growth of PAHs is essential. Therefore, the most important growth mechanisms are reviewed, and presented here from the past four decades (1981-2021) to initiate discussions from a new perspective. Although, the collected and analyzed observations are derived from both experimental, and computational studies, it is neither a systematic nor a comprehensive review. Nevertheless, the mechanisms were divided into three main categories, acetylene additions (e.g. HACA), vinylacetylene additions (HAVA), and radical reactions, and discussed accordingly.

The direct α-arylation of cyclic and acyclic ethers with azoles has been achieved, which features a novel iron-catalyzed cross-dehydrogenative coupling (CDC) process.

Palladium-catalyzed regio- and enantioselective addition of azole heterocycles to alkoxyallenes was developed (up to 92% yields and up to 94% ee). DFT calculations suggest a new Pd(0)-driven mechanistic pathway proceeding through protonation of the Pd-coordinated allene (4-PdL₂), which develops a strongly nucleophilic character at the central C atom.