Helicity control in the synthesis of helicenes and related compounds*
Ivo Starý, Irena G. Stará, Zuzana Alexandrová, Petr Sehnal, Filip Teplý, David Šaman, and Lubomír Rulíšek
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6, Czech Republic
Abstract: Asymmetric synthesis of helicenes and their congeners has been demonstrated to rely either on enantioselective Ni0/PR3*-catalyzed [2+2+2] cycloisomerization of triynes or on diastereoselective CoI-catalyzed [2+2+2] cycloisomerization of chiral triynes. The former approach providing tetrahydrohelicenes in a nonracemic form requires further development as moderate enantioselectivities (up to 54 % ee) have so far been achieved under kinetic control. The latter approach affording helicene-like structures in a diastereomerically enriched form allows for reaching good to excellent diastereoselectivities (up to 100:0) under thermodynamic control.
Keywords: helicenes; cycloisomerization; asymmetric synthesis; enantioselective catalysis; diastereoselectivity.
*Pure Appl. Chem. 78, 197-523. An issue of reviews and research papers based on lectures presented at the 13th IUPAC International Symposium on Organometallic Chemistry Directed Towards Organic Synthesis (OMCOS-13), Geneva, Switzerland, 17-21 July 2005.