Product Class 4: Benzo[b]thiophenes

This chapter is a revision of the earlier Science of Synthesis Section 10.4. It describes methods for the synthesis of benzo[b]thiophenes and related compounds by ring closure or by modification of existing substituent(s) on the benzo[b]thiophene skeleton. Ring-closure methods typically involve the formation of the five-membered ring starting from benzene derivatives bearing substituents such as halogen, alkenyl, alkynyl, or sulfanyl groups at appropriate positions. Ring closure to form the benzene ring can also be achieved using suitably substituted thiophene derivatives. In particular, a number of new methods involving metal-catalyzed C-C and C–S bond formation that have been developed since the previous review are included. Recent years have also witnessed substantial progress in the methods available to directly introduce new substituents to the 2- and 3- positions of benzo[b]thiophenes through metal-catalyzed C-H bond functionalization, and these are included in this chapter.