An Iterative Approach to Unsaturated and Partially Saturated [7]Helicenes.

We report a simple, iterative strategy for the synthesis of [7]helicenes starting from substituted 1,4-xylene building blocks. In the first step, we take advantage of the deprotonatable methyl groups to achieve ethano-bridged dimers. These are oxidatively coupled (without using metal-containing catalysts or light) using a hypervalent iodine reagent. Both steps are repeated to obtain the respective σ/π-helicenes. The degree of saturation can be controlled thermally during the oxidative coupling.