The C—H bond functionalization by transition metal is one of the essential contents in organic chemistry. And it has become an enabling tool in the synthesis of drugs. This review describes the classical reactions of C—H bond functionalization and focus on arylation, alkenylation, alkylation, halogenation, hydroxylation, amination, and insertion which provide a simple and rapid way for the drug synthesis. The detail of the applications and relevant mechanisms are also described. Finally we look forward to its development prospects in this field.

Contents
1 Introduction
2 C—C bond formation
2.1 sp² C—H functionalization assisted by the directing group
2.2 sp² C—H functionalization without the directing group
2.3 sp³ C—H functionalization assisted by the directing group
2.4 sp³ C—H functionalization without the directing group
3 C—H insertion
4 C—X bond formation
4.1 C—X bond formation assisted by the directing group
4.2 C—X bond formation without the directing group
5 Conclusion and outlook