Superacid‐catalyzed Friedel–Crafts phosphination of 2‐hydroxybiphenyls with phosphorus trichloride

Cyclic phosphorus compounds, 6 H ‐dibenz[ c , e ][1,2]oxaphosphorin‐6‐oxide derivatives, were efficiently synthesized by the Friedel–Crafts reaction of 2‐hydroxybiphenyls with phosphorus trichloride in the presence of superacids, especially trifluoromethanesulfonic acid (Tf OH ) as a catalyst. Tf OH was investigated for the first time as an effective catalyst for the aromatic phosphination of 2‐hydroxybiphenyls.