A Versatile Synthesis of Functionalized Pentahelicenes

A general synthetic methodology for the preparation of functionalized (hetero)helicenes has been developed It employs the sequence or a double propargyl ganometallics (Li, Mg, Ga/In) addition to it tolan-2.2'-dialdehyde-type intermediate. a cobalt-catalyzed/cobalt-media led [2 + 2 + 2] cycloisomerization of a triyne intermediate,and a double silica gel-assisted acetic acid elimination to receive pentahelicene, 1,14-diazapentahelicene. and 3,12-dichloro-, 3 12-dichloro-7trimethylsilyl- and 3,12-di-tert-butylpentahelicene 3,12-Dichloropentahelicene undergoes a Suzuki-Miyam a coupling with aryl boronic acids (or ester) under palladium catalysis to afford 3-12-diarylpentahelicenes