| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2006: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2005: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
Fluorine possesses (1) α-carbocation stabilizing effect caused by donation of its unshared electron pair to the vacant p-orbital of the α-carbon, despite (2) its leaving group ability as a fluoride ion (F^-) due to its high electronegativity. We have accomplished the synthesis of fused polyaromatic compounds starting from gem-difluoroalkenes (1,1-difluoro-1-alkenes) via the reactions where both of the two properties were fully utilized.
1,1-Difluoro-1-alkenes bearing a phenyl group at the C-3, 4, or 5 position were treated with FSO_3H・SbF_5 to undergo Friedel-Crafts cyclization via α-fluorocarbocations, followed by spontaneous hydrolysis of the C-F bond to afford bicyclic ketones including a five, six, or seven-membered ring.
The key step in the above mentioned cyclization was the Friedel-Crafts-type reaction, where Magic acid was required to activate the difluoroalkene moiety. To avoid such strong acidic conditions, we have succeeded to conduct this type of cyclization by transition met
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al complexes, such as cationic Pd, Ru, and Au complexes. Especially, [Pd(MeCN)_4](BF_4)_2 effectively promoted the cyclization to give polycyclic products.
On treatment with Magic acid, the difluoroalkenes bearing two aryl groups underwent the domino cyclization via successively generated two kinds of α-fluorocarbocations, which were trapped by the intramolecular aryl groups to construct two 6-membered rings. The cyclized products were readily dehydrogenated to afford substituted helicenes. Using this strategy we have accomplished the syntheses of [4] to [6]helicenes from easily available compounds in only three steps: (i) the preparation of 1,1-difluoro-1-alkenes, (ii) the domino Friedel-Crafts-type cyclization, and (iii) dehydrogenation.
Treatment of 2-trifluoromethyl-1-alkenes bearing an aryl group with Et_2AlCl induced Friedel-Crafts-type cyclization via attack of the aryl group on the carbon γ to the fluorine to give exo-difluoromethylene-substituted cyclic compounds, the helicene precursors. Less
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