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    Asymmetric Synthesis of Nonracemic 2-Amino[6]helicenes and Their Self-Assembly into Langmuir Films

    Year: 2018

    Journal: J. Org. Chem., Volume 83, MAY 18, page 5523–5538

    Authors: Karras, Manfred; Holec, Jan; Bednarova, Lucie; Pohl, Radek; Schmidt, Bernd; Stara, Irena G.; Stary, Ivo

    Organizations: Czech Science Foundation [16-08294S]; Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences [RVO: 61388963]; German Academic Exchange Service (DAAD-fellowship) [57314603]; Ministry of Education, Youth and Sports of the Czech Republic [LM2015073]

    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.
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