Alkynes as Linchpins for the Additive Annulation of Biphenyls: Convergent Construction of Functionalized Fused Helicenes

Abstract

A new approach to fused helicenes is reported, where varied substituents are readily incorporated in the extended aromatic frame. From the alkynyl precursor, the final helical compounds are obtained under mild conditions in a two-step process, in which the final C-C bond is formed via a photochemical cyclization/ dehydroiodination sequence. The distortion of the π-system from planarity leads to unusual packing in the solid state. Computational analysis reveals that substituent incorporation perturbs geometries and electronic structures of these nonplanar aromatics.

Alkynes as Synthetic Equivalents of Ketones and Aldehydes: A Hidden Entry into Carbonyl Chemistry

“…Furthermore, hidden behind these “obvious” traits are other more subtle aspects of this functional group’s appeal. For example, alkynes can be considered as super-stabilized 1,2-dicarbenes [4,5], as well as a perfect atom-economical, carbon-rich building unit for the preparation of extended polyaromatics [3,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23].…”

Highly Regioselective Domino Benzannulation Reaction of Buta‐1,3‐diynes To Construct Irregular Nanographenes

“…[2] Bottom-up approaches for the production of well-defined nanographenes have attracted significant interest of chemists. [3] The Scholl reaction, [4] transition-metal- [5] or photocatalyzed [6] directed intramolecular arylation reactions, and alkyne benzannulation reactions (inter-and intramolecular) [7] are widely used in the key C-C bond-forming reaction of nanographene syntheses. Moreover, the preparation of carbonrich materials from precursors containing many C-C triple bonds is gaining more attention.…”

Nanographene and Graphene Nanoribbon Synthesis via Alkyne Benzannulations

“…Molecular structure can greatly affect the properties exhibited by the bulk material, hence, it is important to understand how subtle changes to the molecular structure affect the HOMO/LUMO energy gaps, crystal packing, or UV-vis absorption and emission [34]. The way in which the twisted molecular structure of helicenes pack was of interest to the Alabugin group, who made [5]helicene-like compounds under metal-free conditions [35]. The reaction proceeds via an ICl-promoted alkyne benzannulation of 25 to afford either iodophenanthrene 26 , iodochrysene 27 , or a mixture of both (Scheme 6).…”

“…The Alabugin group has done significant work over the past few years using high-energy alkyne-containing substrates to produce a host of NGs through thermodynamically “downhill” alkyne benzannulations [35,39,40,41,42,43,44]. Their recent work stems from their initial discovery that tin-mediated radical cascade cyclizations of alkynes can be used to afford substituted benzo[a]indeno[2,1-c]fluorenes and other products [45].…”