Pseudohelical and Helical Primary Structures of 1,2-Spiroannelated Four- and Five-Membered Rings: Syntheses and Chiroptical Properties

详细信息    查看全文

• 作者：Tien Widjaja ; Lutz Fitjer ; Aritra Pal ; Hans-Georg Schmidt ; Mathias Noltemeyer ; Christian Diedrich ; Stefan Grimme
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：November 23, 2007
• 年：2007
• 卷：72
• 期：24
• 页码：9264 - 9277
• 全文大小：332K
• 年卷期：v.72,no.24(November 23, 2007)
• ISSN：1520-6904

文摘

The pseudohelical hydrocarbons (R)-6, (S)-7, and (R)-8 and the helical hydrocarbon (P)-9, formally derivedfrom the helical hydrocarbon (P)-4 by stepwise replacement of each of the four-membered rings by afive-membered ring, have been prepared. Their optical rotations vary systematically, both in magnitudeand sign. Of the extremes, (P)-4 represents the usual case of a right-handed dextrorotatory helix, while(P)-9 represents the unusual case of a right-handed levorotatory helix. To rationalize these facts, DFTcalculations of the rotatory power of (P)-helices of three-, four-, and five-membered rings have beenperformed. The results show a very good agreement with the experimental data for the rigid helices ofthree-membered rings and always show the correct sign and order of magnitude for the flexible helicesof four- and five-membered rings for which Boltzmann-averaged optical rotations of up to six conformershad to be used. Within the conformers of the latter, a set of large dihedral angles for the bonds of theinner sphere correspond to a high specific rotation, and a set of small dihedral angles correspond to alow specific rotation. As a consequence, the Boltzmann-averaged values markedly depend on the geometryand weight of the conformers involved.