Synthesis, Structures, and Properties of 蟺-Extended Double Helicene: A Combination of Planar and Nonplanar 蟺-Systems

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• 作者：Takao Fujikawa ; Yasutomo Segawa ; Kenichiro Itami
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：June 24, 2015
• 年：2015
• 卷：137
• 期：24
• 页码：7763-7768
• 全文大小：550K
• ISSN：1520-5126

文摘

The synthesis, structures, and properties of a 蟺-extended double helicene 1 are described. This double helicene 1 was synthesized by a four-fold oxidative C鈥揌 biphenylation of naphthalene followed by the Scholl reaction or via five steps including the Suzuki鈥揗iyaura cross-coupling reaction and the Scholl reaction. Due to the two helical substructures, 1 has three isomers, i.e., two enantiomers in a twisted form [(P,P) and (M,M)] and one diastereoisomer in a meso form. X-ray crystallographic analysis of the twisted isomers (twisted-1) revealed a tightly offset packing pattern of (P,P)- and (M,M)-twisted isomers, affording a three-dimensional lamellar stacking structure. A high isomerization barrier (43.5 kcal mol^鈥?) and the relative thermal stability of twisted-1 isomer over meso-1 by 0.9 kcal mol^鈥? were estimated by DFT calculations. The three isomers were successfully separated by chiral HPLC and characterized by circular dichroism spectroscopy as well as by TD-DFT studies. Electronic state variation resulting from the molecular geometry difference between the two diastereoisomers (twisted-1 and meso-1) was observed by UV鈥搗is absorption and fluorescence spectra.