Copper‐Catalyzed C2 and C3 Phosphonation of Benzofuran and Benzothiophene with Trialkyl Phosphites

A strategy for the selective phosphonation of benzofuran and benzothiophene with trialkyl phosphites was developed. In these reactions, the C−H phosphonation of benzofurans or benzothiophenes at the C2 or C3 position with trialkyl phosphites was successfully achieved without directing groups by using a copper catalyst. Additionally, the C5 phosphonation of furan was successful under the same conditions.