Synthesis of azahelicenes through Mallory reaction of imine precursors: corannulene substrates provide an exception to the rule in oxidative photocyclizations of diarylethenes
Animesh Ghosh, Dániel Csókás, Maja Budanović, Richard D. Webster, Imre Pápai, Mihaiela C. Stuparu
Abstract
Typically, the synthesis of phenanthrene-based polycyclic aromatic hydrocarbons relies on the Mallory reaction. In this approach, stilbene (PhCH[double bond, length as m-dash]CHPh)-based precursors undergo an oxidative photocyclization reaction to join the two adjacent aromatic rings into an extended aromatic structure. However, if one C[double bond, length as m-dash]C carbon atom is replaced by a nitrogen atom (C[double bond, length as m-dash]N), the synthesis becomes practically infeasible. Here, we show the very first examples of a successful Mallory reaction on stilbene-like imine precursors involving the molecularly curved corannulene nucleus. The isolated yields exceed 90% and the resulting single and double aza[4]helicenes exhibit adjustable high affinity for electrons.