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

J Org Chem. 2018 May 18;83(10):5523-5538. doi: 10.1021/acs.joc.8b00538. Epub 2018 Apr 30.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't