Recent Developments in the Synthesis of Helicene‐Like Molecules

Abstract

Straightforward access to helicene‐like molecules (see structure) is possible by short and efficient protocols that have emerged in the past few years. These transformations, as well as recent approaches to chiral nonracemic derivatives, constitute a significant advancement in synthetic methodology.

Asymmetric Catalysis in the [2+2+2] Cycloaddition of Arynes and Alkynes: Enantioselective Synthesis of a Pentahelicene

“…[5,6] The development of novel synthetic approaches to these interesting molecules, particularly in enantioselective fashion, continues to be a challenge. [7,8] We reasoned that the use of chiral ligands in the metal-catalyzed cycloaddition of polycyclic arynes with alkynes could be applied to the development of an enantioselective synthesis of chiral helicenes, and would constitute the first example of an asymmetric [2 + 2 + 2] cycloaddition reaction involving arynes. Here we report the first results of our efforts to achieve this goal.…”

Preparation of cyclic molecules bearing “strained” olefins using olefin metathesis

“…Although strained, the normally competing reverse ringopening reaction would not be possible. Olefin metathesis represents a novel and mild method to access these carbon skeletons (Scheme 10) [36]. Two optimal protocols for the formation of [5] helicene from the divinyl precursor 33 were developed that can form the benzene ring despite the strain in the final structure.…”

Molecular structures and electronic properties of helical thiophene carbon–sulfur oligomers, H2(C2S) n C2H2 (n = 1–20)

“…Thiophene-based annulations of linear b-oligothiophenes giving helical carbon-sulfur (C 2 S) n oligomers for large n and possessing moderate curvature characteristic of helicenes were noted [6]. As helical molecules are attractive building blocks for the development of materials with novel optical properties, highly annulated helical structures including heterohelicenes were widely synthesized [15][16][17][18][19][20][21]. Chiral properties of [n]helicenes with n ortho-fused aromatic rings [22] were studied.…”