TY  - JOUR
A1  - Karras, Manfred
A1  - Holec, Jan
A1  - Bednarova, Lucie
A1  - Pohl, Radek
A1  - Schmidt, Bernd
A1  - Stara, Irena G.
A1  - Stary, Ivo
T1  - Asymmetric Synthesis of Nonracemic 2-Amino[6]helicenes and Their Self-Assembly into Langmuir Films
JF  - The journal of organic chemistry
N2  - Alternative ways of preparing nonracemic 2-amino[6]helicene derivatives were explored. The enantioselective [2 + 2 + 2] cycloisomerization of a nonchiral triyne under Ni(cod)(2)/(R)-QUINAP catalysis delivered the enantioenriched (+)-(P)-2-aminodibenzo[6]helicene derivative in 67% ee. An ultimate "point-to-helical" chirality transfer was observed in the cyclization of enantiopure triynes mediated by Ni(CO)(2)(PPh3)(2) affording (-)-(M)- or (+)-(P)-7,8-bis(p-tolyl)hexahelicen-2-amine in >99% ee as well as its benzoderivative in >99% ee. The latter mode of stereocontrol was inefficient for a 2-aminobenzo[6]helicene congener with an embedded five-membered ring. The rac-, (-)-(M)-, and (+)-(P)-7,8-bis(p-tolyl)hexahelicen-2-amines formed Langmuir monolayers at the air water interface featuring practically identical surface pressure vs mean molecular area isotherms. The corresponding Langmuir-Blodgett films on quartz or silicon substrates were characterized by UV vis/ECD spectroscopy and AFM microscopy, respectively.
Y1  - 2018
U6  - https://doi.org/10.1021/acs.joc.8b00538
SN  - 0022-3263
SN  - 1520-6904
VL  - 83
IS  - 10
SP  - 5523
EP  - 5538
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Karras, Manfred
A1  - Dabrowski, Michal
A1  - Pohl, Radek
A1  - Rybacek, Jiri
A1  - Vacek, Jaroslav
A1  - Bednarova, Lucie
A1  - Grela, Karol
A1  - Stary, Ivo
A1  - Stara, Irena G.
A1  - Schmidt, Bernd
T1  - Helicenes as Chirality-Inducing Groups in Transition-Metal Catalysis
BT  - the first helically chiral Olefin Metathesis Catalyst
JF  - Chemistry - a European journal
N2  - Helical chirality is a novel enantioselectivity-inducing property in transition-metal-catalyzed transformations. The principle is illustrated herein for the example of asymmetric olefin metathesis. This work reports the synthesis of the first helically chiral Ru-NHC alkylidene complex from an aminohelicene-derived imidazolium salt, which was ligated to the first generation Hoveyda-Grubbs catalyst. Kinetic data were acquired for benchmark test reactions and compared to an achiral catalyst. The helically chiral Ru-catalyst was evaluated in asymmetric ring-closing metathesis (RCM) and ring-opening metathesis-cross-metathesis (ROM/CM) reactions, which proceeded with promising levels of enantioselectivity. Extensive NMR-spectroscopic investigations and a DFT geometry optimization were performed. These results led to a topographic steric map and calculation of percent-buried-volume values for each quadrant around the metal center.
KW  - asymmetric catalysis
KW  - carbene ligands
KW  - helicenes
KW  - metathesis
KW  - ruthenium
Y1  - 2018
U6  - https://doi.org/10.1002/chem.201802786
SN  - 0947-6539
SN  - 1521-3765
VL  - 24
IS  - 43
SP  - 10994
EP  - 10998
PB  - Wiley-VCH
CY  - Weinheim
ER  -