Chimerical pyrene-based [7]helicenes as twisted polycondensed aromatics.
Chimerical pyrene-based dibenzo[7]helicene rac-1 and 2H-pyran[7]helicene (M,R,R)-(-)-2, in which two pyrene subunits are fused to the [7]helicene/[7]heterohelicene scaffold, were synthesised by means of Ni(0) - or Co(I) -mediated [2+2+2] cycloisomerisation of dipyrenyl-acetylene-derived triynes. Pyrene-based dibenzo[7]helicene 1 was obtained in enantioenriched form by enantioselective cycloisomerisation under Ni(0) /QUINAP catalysis (57 % ee) or in enantiopure form by racemate resolution by liquid chromatography on a chiral column. 1,3-Allylic-type strain-controlled diastereoselective cycloisomerisation was employed in the synthesis of enantiopure (M,R,R)-(-)-2. Physicochemical properties of 1 and 2 encompassing the helicity assignment, stability to racemisation, X-ray crystal structure, UV/Vis, experimental/calculated electronic circular dichroism and fluorescence spectra were studied. Accordingly, comparison of the X-ray crystal structure of (M,R,R)-(-)-2 with calculated structures (DFT: B3LYP/cc-pVDZ, B97D/cc-pVDZ) indicated that its helical backbone is slightly over-flattened owing to intramolecular dispersion forces between tert-butylated pyrene subunits. Both 1 and 2 are fluorescent (with quantum yields in dichloromethane of ΦF =0.10 and 0.17, respectively) and are suggested to form intramolecular excimer states upon excitation, which are remarkably stabilised and exhibit large Stokes shifts (296 and 203 nm, respectively).
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133.
Michal
M
Buchta
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133.
Jiří
J
Rybáček
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133.
Andrej
A
Jančařík
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133.|Department of Chemistry, Memorial University, St. John's, NL A1B 3X7 (Canada), Fax: (+1) 709-864-3702.
Amit A
AA
Kudale
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133.
Miloš
M
Buděšínský
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133.
Jana Vacek
JV
Chocholoušová
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133.
Jaroslav
J
Vacek
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133.
Lucie
L
Bednárová
Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, 128 43 Prague 2 (Czech Republic).
Ivana
I
Císařová
Department of Chemistry, Memorial University, St. John's, NL A1B 3X7 (Canada), Fax: (+1) 709-864-3702. gbodwell@mun.ca.
Graham J
GJ
Bodwell
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133. stary@uochb.cas.cz.
Ivo
I
Starý
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6 (Czech Republic), Fax: (+420) 220-183-133. stara@uochb.cas.cz.
Irena G
IG
Stará
alkynes; asymmetric synthesis; chirality; cycloisomerisation; helical structures