Directed C–H alkylation of benzenes
Directed C-H alkylations of benzenes involve the net substitution of hydrogen ortho to a directing group in a substituted benzene for an alkyl group. This subset of directed C–H functionalization reactions refers specifically to alkylations of substituted benzenes, which involve their reaction with alkenes, organometallic reagents, or organic electrophiles at a C–H bond ortho to a Lewis basic directing group. These reactions are catalyzed by transition metal complexes containing a wide variety of different metals. Many types of Lewis basic directing groups can be employed to form cyclometalated species in which the ortho C–H bond has broken. Directed alkylations of substituted benzenes are less common in organic synthesis than directed oxidations or arylations, although a reported synthesis of (+)-lithospermic acid uses this reaction as a key step.