Efficient large-scale synthesis of 9-alkylfluorenyl phosphines for Pd-catalyzed cross-coupling reactions

The reactions of aliphatic alcohols with fluorene coupled with a transfer hydrogenation result in the facile formation of 9-alkylfluorenes, whose deprotonation with nBuLi and quenching of the fluorenyl anion with Cy2PCl in MTBE gave 9-alkylfluorenyl-dicyclohexyl phosphines, which are conveniently isolated as the respective phosphonium tetrafluoroborates after treatment with aqueous HBF4. This route enables the facile large-scale (kilogram) synthesis of new ligands highly effective in Pd-catalyzed cross-coupling reactions.