Palladium-Catalyzed Double C-H Activation Directed by Sulfoxides in the Synthesis of Dibenzothiophenes

摘要

C-H functionalization is a sustainable and straightforward approach to complex substances. Numerous practical methods for the formation of C-C, C-N, and C-O bonds through direct C-H activation have been developed using transition-metal catalysis. The activation of C(sp~2)-H bonds of aromatic compounds provides access to key scaffolds of natural products, drugs, and materials. Double C-H activation is a challenging, attractive, and highly economical method to create C-C biaryl bonds. However, the previously developed methods often suffer from selectivity problems in the formation of substituted biaryls and require a great excess of one coupling partner. For the efficient solution to this problem a number of directing groups such as carbonyl-based or nitrogen-containing groups have been used. The development of efficient methods for the construction of complex molecules by multiple C-H functionalization poses a great challenge. Herein, we report our preliminary results on a palladium-catalyzed double C-H activation using sulfoxide as a new traceless directing group, and its application in a highly regioselective synthesis of polysubstituted dibenzothiophenes through a cascade reaction (Scheme 1).