Fujikawa T, Segawa Y, Itami K. Laterally π-Extended Dithia[6]helicenes with Heptagons: Saddle-Helix Hybrid Molecules.
J Org Chem 2017;
82:7745-7749. [PMID:
28686025 DOI:
10.1021/acs.joc.7b01540]
[Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A laterally π-extended dithia[6]helicene 1, representing an interesting saddle-helix hybrid molecule containing an unusual heptagon, has been synthesized by MoCl5-mediated oxidative stitching of tetrakis(thienylphenyl)naphthalene precursor 2 involving reactive-site capping by chlorination and subsequent Pd-mediated dechlorination of tetrachlorinated intermediate 1-Cl4. Highly distorted, wide helical structures of dithia[6]helicenes (1 and 1-Cl4) were clarified by single-crystal X-ray diffraction analyses where heterochiral slipped π-π stacking was displayed in a one-dimensional fashion. Notably, theoretical studies on the thermodynamic behavior of 1 predicted an extraordinarily high isomerization barrier of 49.7 kcal·mol-1, which enabled optical resolution and chiroptical measurements. Electronic structures of these huge helicenes were also examined by photophysical and electrochemical measurements.
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