Organic Letters
Letter
3m, affording the halogen-substituted dibenzo[g,p]chrysenes 4d,
4g, 4h, 4l, and 4m, in good yields.
A plausible reaction mechanism for this cyclization is shown in
Scheme 3. First, protonation of the difluoroethene moiety in 3a
trifluoro-2-iodoethane or 1,1-difluoroethene. Dibenzo[g,p]-
chrysenes possess a double helical structure due to the presence
of two inherent helicene moieties. Their application to new
electronic materials will be stimulated by the approach presented
in this study.
Scheme 3. Proposed Reaction Mechanism
ASSOCIATED CONTENT
* Supporting Information
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The Supporting Information is available free of charge on the
Experimental details, characterization data, and NMR
AUTHOR INFORMATION
Corresponding Author
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This research is partly supported by MEXT/JSPS KAKENHI
(J.I., No. 25288016), the Asahi Glass Foundation (J.I.), and
Izumi Science and Technology Foundation (T.F.). We acknowl-
edge the generous gifts of (CF3)2CHOH (HFIP) from Central
Glass Co., Ltd. and CF3CH2I from Tosoh F-Tech, Inc.
regioselectively generates the cationic intermediate A, in which
the carbocation is stabilized by the α-fluorine substituents. A
Friedel−Crafts-type cyclization followed by the elimination of
HF allows C−C bond formation and vinylic C−F bond cleavage
to afford 9-(biphenyl-2-yl)-10-fluorophenanthrene 10a. The
second cyclization is induced by the protonation of the
phenanthryl moiety in 10a. Thus, a further Friedel−Crafts-type
cyclization proceeds through the fluorine-stabilized arenium ion
B,10 resulting in aromatic C−F bond cleavage.17
To gain some experimental evidence to support the proposed
reaction mechanism, we attempted the acid-mediated cyclization
of fluorophenanthrene 10a, which was prepared via cyclization of
3a with TiF4 in CH2Cl2 (Table 1, entry 9). Treatment of 10a with
magic acid or TiF4 in HFIP−CH2Cl2 (10:1) or HFIP afforded
dibenzo[g,p]chrysene (4a) in excellent yields (Scheme 4). These
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