2‑Bromo[6]helicene as a Key Intermediate for [6]Helicene Functionalization

The synthesis of 2-bromo[6]­helicene was revised and improved up to 51% yield. Its reactivity was thoroughly investigated, and a library of 17 different carbon, boron, nitrogen, phosphorus, oxygen and sulfur substituted derivatives was prepared. The racemization barrier for 2-bromo[6]­helicene was determined, and the usage of enantiomers in the synthesis of optically pure helicenes was rationalized. The three most energy-demanding reactions using enantiomerically pure 2-bromo[6]­helicene were tested in order to confirm the predicted enantiomeric excess.