Transition metal catalysed synthesis of tetrahydro derivatives of [5]-, [6]- and [7] helicene

Article abstract of DOI:10.1016/S0040-4039(99)00099-4

Tetrahydro analogues of [5]-, [6]- and [7] helicene have been easily prepared by intramolecular [2+2+2] cycloisomerization of appropriate triynes under CpCo(CO)₂/PPh₃ or Ni(cod)₂/PPh₃ catalysis. This nonphotochemical methodology allows enantioselective synthesis of a helical skeleton employing the Ni(cod)₂/(S)-(-)-MOP catalytic system. On reaction with DDQ, tetrahydro[5]helicene was transformed to [5]helicene.