Diethyl chloro(methylthio)methylphosphonate (3) reacted with arenes and alk-1-enes in the presence of a Lewis acid to give the Friedel–Crafts product (5) and the ene product (8), respectively. The Pummerer rearrangement product (4) derived from diethyl (methylsulphinyl)methylphosphonate (10) also reacted with alk-1-enes in trifluoroacetic acid to give the products (8).