Rhodium(III)-Catalyzed C-H Activation and Annulation with 1-Alkynylphosphine Sulfides: A Mild and Regioselective Access for the Synthesis of Bulky Phosphine Ligands.

We reported herein rhodium(III)-catalyzed C-H activation and annulation reactions for the synthesis of bulky phosphine ligands by using 1-alkynylphosphine sulfides as key starting materials. In the presence of [Cp*RhCl2]2 (5 mol %) and CsOAc (2.0 equiv), various N-(pivaloyloxy)benzamides (3.0 equiv) could react smoothly with 1-alkynylphosphine sulfides at 40 °C in MeOH/CF3CH2OH cosolvent without external oxidant. Using [Cp(Ph)RhCl2]2 as catalyst, the reaction can be performed under less loading of benzamides (2.0 equiv) and milder reaction conditions (25 °C) with higher regioselectivity. In a sequential cyclization/desulfidation process, this new method provides a variety of bulky heteroarylphosphines with an isoquinolin-1(2H)-one motif.