BF<sub>3</sub> ⋅ Et<sub>2</sub>O‐Mediated Annulation of 2‐Alkynyl Biaryls with <i>N</i>‐(Arylthio) Succinimides: An Efficient Approach to Access 9‐Sulfenylphenanthrenes
A simple and effective method for the synthesis of 9-sulfenylphenanthrenes was developed. The reaction proceeds through BF3 ⋅ OEt2-mediated annulation of 2-alkynyl biaryls with N-arylthio succinimides at roomtemperature. With this method, a series of 9-sulfenylphenanthrenes was efficiently obtained in good to excellent yields under mild and metal-free conditions.