An enzymatic electrophilic aromatic substitution reaction

The electrophile in an enzymatic S_EAr reaction is usually a carbocation.  One example of an S_EAr reaction can be found in the biosynthesis of vitamin K.  In this reaction, an isoprenoid chain is transferred to a phenol ring as part of the  and related biomolecules. In this example, carbocation intermediate B is stabilized by resonance with the electron-donating phenol oxygen.