Building Blocks for Acetylenic Scaffolding Inspired by 6,6,12‐Graphyne

Acetylenic scaffolding is a synthetic method for the preparation of large, carbon‐rich frameworks using acetylenic coupling reactions. Segments of the elusive carbon allotrope 6,6,12‐graphyne present acetylenic frameworks that are particularly challenging to synthesize. Here, we present the development of a variety of molecular building blocks to advance the synthesis of such segments. The modules are derived from tri‐ and tetraethynylethene derivatives, di‐ and tetraethynyl‐substituted tolane derivatives, and cyclic dehydroannulene and radiaannulene derivatives with peripheral alkyne substituents. The compounds were prepared by a combination of selective desilylation of trialkylsilyl‐protected enyne compounds and Sonogashira coupling reactions of the terminal alkynes with suitable aryl or vinyl halides. One example involves a novel and simple synthesis of tetra‐substituted tetraethynylethenes in the cis configuration from a readily available starting material; such compounds have hitherto required a multistep and tedious protocol to prepare. Moreover, aluminum chloride‐mediated conversion of trimethylsilyl‐substituted terminal alkynes into ketone functionalities upon treatment with acid chloride substrates is presented as a convenient way of achieving useful building blocks. Intramolecular cyclization via a McMurry coupling of the dione allowed the ready synthesis of a functionalized dehydroannulene, presenting an alternative to the Sonogashira cyclization approaches used previously to form this core.