Study On The Synthesis Of Thiochrome[2,3-b] Indol/Aryl Sulfides Compounds With C-S Bonds Based On El Emental Sulfur

The utility of concise approaches to establish valuable skeletons from simple,inexpensive,and readily available substrates has emerged as a new avenue in organic synthesis owing to its atom economy and simplified procedure.The synthetic significance of this concept would be enhanced to achieve the preparation of S-containing compounds.Elemental sulfur doping in the ring systems could modulate functional components.And it has been recognized as a powerful strategy by harnessing elemental sulfur as the sulfur source to construct S-containing compounds.Inspired by considerable efforts in the preparation of S-containing compounds,we envisioned the possibility of elemental sulfur incorporated indole and 2-bromobenzylaldehyde to produce the desired thiochromeno[2,3-b]indole.Subsequently,we have conducted the formation of C-S bond in the presence of elemental sulfur and 2-bromobenzene derivatives.1.Elemental sulfur-promoted [2+3+1] annulation for the straightforward synthesis of functionalized thiochromeno[2,3-b]indoles from indole derivativesAn intermolecular [2+3+1]annulation between indole and 2-bromobenzylaldehyde derivatives was successfully achieved by utilizing elemental sulfur as the promoter and coupling partner.The cross-cyclization was compatible with a diverse range of indole and 2-bromobenzaldehyde.This direct and operationally simple procedure provided a rapid and reliable approach to synthesize functionalized thiochromeno[2,3-b]indoles.Preliminary mechanism studies have shown that elemental sulfur enhances the nucleophilicity of the indole 3 to attack the aldehyde group,and the hydrogen in the aldehyde group is not eliminated.In addition,cleavage of the indole C-H bond is not the rate-determining step of the reaction.2.Elemental sulfur participated in the construction of aryl sulfidesWe have developed a new strategy on elemental sulfur involving the formation of C-S bond from 2-bromobenzene derivatives.This stategy offered a convenient access to diverse diaryl sulfides.This cross coupling was compatible with a diverse range of aryl bromide bearing electron-withdrawing group.Regretfully,aryl bromide bearing electron-donating group was not suitable for this transformation.Preliminary mechanistic studies demonstrated that the radical process was not involved in the formation of C-S bond.This reaction was also conducted by metal-free condition.