The synthesis of extremely long helicenes and their electrical conductivity
The group of Dr. Ivo Starý has reported the synthesis of oxahelicenes comprising up to 19 fused rings that beats the current record in the length of a helicene backbone. The use of a flow reactor in the key step, the final multiple cobalt-mediated alkyne [2+2+2] cycloisomerization to form up to 12 rings in a single operation, was found to be advantageous for the efficient folding of the aromatic oligoynes into helical oxahelicenes. The stereogenic centers in enantiomerically pure substrates steered the diastereoselective polycyclization of the oligoynes. Single-molecule conductance was measured by the break-junction method. The long helicenes have been envisaged to be attractive materials for nano- and chiroscience.
J. Nejedlý, M. Šámal, J. Rybáček, M. Tobrmanová, F. Szydlo, C. Coudret, M. Neumeier, J. Vacek, J. Vacek Chocholoušová, M. Buděšínský, D. Šaman, L. Bednárová, L. Sieger, I. G. Stará, I. Starý:
Synthesis of Long Oxahelicenes by Polycyclization in a Flow Reactor.
Angewandte Chemie International Edition, online from 18 April 2017.