Q87852110
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A series of diverse aromatic azadienetriyne and azatriynes was synthesised. These compounds were subjected to transition metal-mediated [2+2+2] cycloisomerisation to form pentacyclic or hexacyclic helically chiral azahelicene or azahelicene-like structures mostly in moderate yields. Introducing stereogenic centre(s) into selected azatriynes, cyclisation proceeded in a stereoselective fashion providing aza[5]helicenes or aza[6]helicene-like compounds in up to a 100:0 diastereomeric ratio. Gibbs energy differences between corresponding pairs of diastereomers (calculated at the DFT(B3LYP)/TZV+P level) were in good agreement with the experimental data and allowed for the prediction of the stereochemical outcome of the reaction. This study presents for the first time asymmetric synthesis of azahelicene derivatives in high optical purities.
Correlated ab initio calculations on large systems, such as the popular MP2 (or RI-MP2) method, suffer from the intramolecular basis set superposition error (BSSE). This error is typically manifested in molecules with folded structures, characterized by intramolecular dispersion interactions. It can dramatically affect the energy differences between various conformers as well as intramolecular stabilities, and it can even impair the accuracy of the predictions of the equilibrium molecular structures. In this study, we will present two extreme cases of intramolecular BSSE, the internal stability of [n]helicene molecules and the relative energies of various conformers of phenylalanyl-glycyl-phenylalanine tripeptide (Phe-Gly-Phe), and compare the calculated data with benchmark values (experimental or high-level theoretical data). As a practical and cheap solution to the accurate treatment of the systems with large anticipated value of intramolecular BSSE, the recently developed density functional method augmented with an empirical dispersion term (DFT-D) is proposed and shown to provide very good results in both of the above described representative cases. (c) 2007 Wiley Periodicals, Inc.
The review deals with the chemistry of helically chiral polyaromatics represented by helicenes. Attention is paid to synthetic methods that can be used for the preparation of helicenes, heterohelicenes and helicene analogues. Of them, the Co- or Ni-catalysed [2+2+2] cycloisomerisation of aromatic triynes to form the helical scaffold, a method developed at the Institute is reviewed. After six decades of helicene chemistry, the interest in these unique aromatic compounds is gradually increasing. As the synthesis of helicenes has recently witnessed a significant progress, their applications in various branches of chemistry, physics and nanoscience can be expected.
- Klíčová slova
- heliceny,
- MeSH
- acetylen chemie MeSH
- katalýza MeSH
- pojmy organické chemie MeSH
- polycyklické sloučeniny * chemie MeSH
- stereoizomerie * MeSH
- vztahy mezi strukturou a aktivitou * MeSH
- Publikační typ
- práce podpořená grantem MeSH
By means of selective deuterium labeling of 1-aza[6]helicene combined with resolution of the enantiomers, chiral discrimination in silver(I)-bound dimers of the type [LAgL']+ is probed by electrospray mass spectrometry. The analysis of the results reveals a pronounced preference for the formation of homochiral dimers (P,P and M,M, respectively) over the statistically preferred heterochiral variant (P,M), which is fully consistent with previous data about the formation of homochiral dimers in the condensed phase. Further, competitive experiments with mixtures of 1- and 2-aza[6]helicene suggest a largely preferred coordination of 1-aza[6]helicene to the silver(I) cation.
