Fig. 4: The substrate scope for the regioselective endoalkenes with S=P-OH.

a Reaction condition: Alkynes 4 (0.54 mmol), 2 (0.30 mmol), BF3·OEt2 (0.60 mmol), toluene (2 mL), 100 °C, 4 h.

a Reaction condition: Alkynes 4 (0.54 mmol), 2 (0.30 mmol), BF3·OEt2 (0.60 mmol), toluene (2 mL), 100 °C, 4 h.