Transition-Metal-Catalyzed Intramolecular Cross-Dehydrogenation-Coupling Of Diaryl Sulfoxides

In recent years, the transition-metal-catalyzed of two C-H bonds for C-C coupling has become a promising strategy. Transition-metal-catalyzed cross-dehydrogenative-coupling (CDC) it considered a more efficient and environmentally friendly approach since in circumvents the often tedious and wasteful prefunctionalization of starting materials, such as organic halides and organometallic reagents. Among them, the formation of polycyclic aromatic compounds via transition-metal-catalyzed intramolecular CDC reaction has received considerable attention. A wide variety of nitrogen or oxygen-containing heterocycles such as xanthones, and carbazoles have been synthesized through CDC reaction. However, CDC reaction for the synthesis of sulfur-containing heterocycles remains an outstanding challenge. This dissertation mainly focused on the studies of transition-metal-catalyzed intramolecular CDC reaction of diphenyl sulfoxide.In the presence of PdCl2, the CDC reaction of diphenyl sulfoxide can afford dibenzothiophene-S-oxide product under N2 atmosphere using Ag2O as the oxidant in trifluoroacetic acid. The yield of dibenzothiophene-S-oxide is 58%. With the optimized reaction conditions,2,2’-dimethyldiphenyl sulfoxide resulted in the desired product in good yield. Unfortunately, other substrates afforded the desired products in low yields. The main product of CDC reaction of 4,4’-dimethyldiphenyl sulfoxide was 4,4’-dimethyldibenzothiophene.Derivatives of dibenzothiophene have found use as versatile intermediates in organic synthesis. Further studies showed that the formation of dibenzothiophene can be catalyzed by RhCl3 via CDC reaction and deoxygenation. The optimal catalytic system consists of the use of RhCl3(5 mol%), Ag2CO3 (3 equiv) in TFA at 140℃ for 24h. A 96% yield of dibenzothiophene was obtained. A broad range of functional groups were tolerated under the simple reaction conditions, and a series of dibenzothiophenes with substituents at different positions were obtained in moderate to good yields.