Synthesis of a Pinacol Boronate Precursor for [18F]Rucaparib Radiosynthesis

A novel synthetic approach toward pinacol boronate used as a precursor in the recent radiosynthesis of [¹⁸F]rucaparib is described in this study. The Heck reaction of an ortho‐iodoaniline derivative bearing a chloride group at the meta‐position with acrylonitrile produced the desired (E)‐2‐aminocinnamonitrile derivative. The subsequent cyanide‐catalyzed imino‐Stetter reaction of aldimine derived from the obtained 2‐aminocinnamonitrile and aldehyde afforded the required trisubstituted indole‐3‐acetonitrile. The reduction of the nitrile group with cobalt boride followed by the construction of an azepinone scaffold generated indoloazepinone bearing a chloride substituent at the C6‐position of the indole scaffold. The Suzuki–Miyaura borylation of the chloride substituent produced pinacol boronate previously used in the synthesis of [¹⁸F]rucaparib. Detailed outcomes of different approaches using different 2‐aminocinnamonitriles were discussed as well.