Helicene was recently posted by Molecule of the Day as example of chirality. The post included the link to the Wikipedia page that badly needed updated information. So, when you get to Wikipedia, keep in this in mind…you may miss tons of important stuffs…
Since helicene is one of the two major research projects in our group, we will take on to fill in some information.
Actually, the first racemic [n]helicence, pyrrolohelicene was reported in 1927, followed by the racemic helicence in 1933.
[n]Helicenes structures possess n angularly (ortho) annelated (fused) aromatic rings, in which the steric repulsion of terminal rings force distortion from planarity, leading to helical π-conjugated structures. These molecules possess some of the strongest intrinsic chiral properties. Syntheses of structures with such high degree of ring annelation, and with significant strain are challenging. So, it took a long period of 23 years later before the first successful synthesis of non-racemic helicene was reported by Newman and Lednicer in 1953.
During the 60s and 70s, photochemical syntheses were developed, such method provided numerous [n]helicenes, with helicene as the longest structure consisting of benzene rings. Various [n]helicenes consist of alternating benzene and thiophene rings were also synthesized by the photochemical methods, with the helicene as the longest structure. The photochemical syntheses provided helicenes in low/moderate yield and with limited functionalities.
More posts will follow…perhaps a series of posts on each class of helicene structures.
- Visit this site to see more cool carbon-sulfur helicene structures.
- Recent review articles to read…
- Andrzej Rajca, Suchada Rajca, Maren Pink, Makoto Miyasaka “Annelated, Chiral π-Conjugated Systems: Tetraphenylenes and Helical -Oligothiophenes”, SynLett, 2007,1799 – 1822 (account, invited) [Abstract].
- Andrzej Rajca, Makoto Miyasaka, “Synthesis and Characterization of Novel Chiral Conjugated Materials”, In Functional Organic Materials – Syntheses and Strategies, T. J. J. Mueller, U. H. F. Bunz, Eds.; Wiley-VCH, 2007, Chapter 15, 543-577 [Download]
- Tomás Torroba, María García-Valverde, “Rigid Annulated Carbon-Sulfur Structures”, Angew. Chem. Int. Ed., 2006, 45, 8092-8096. [Abstract]
- Shawn K. Collins, Martin P. Vachon, “Unlocking the potential of thiaheterohelicenes: chemical synthesis as the key”, Org. Biomol. Chem, 2006, 4, 2518-2524. [Abstract]