The Research Of Palladium-catalyzed Desulfitative Arylation And Iron-catalyzed2-arylbenzoxazoles Formation

Heterocyclic compounds are more than100years old since their discovery.Recently, with the development of synthetical and identifiable technology, more andmore heterocyclic compounds were synthesized, and the applied field and purpose ofthem were expended. Indoles, benzoxazoles and their derivatives are ubiquitous inbiochemical, medicinal structures and functional materials. Because of the importantof these compounds, the synthetic methods of them have attracted much attention. Avast number of nobel and efficient approachs have been reported. Combined with therequire of green chemistry development and the research of our group, this paper didsome in-depth resrarch about construction of C-C and C-N bonds environmentallyfriendly in mild reaction conditions.Selective arylation reaction of indoles is one of hot research topics in organicsynthesis. In particular, the direct arylation of indoles via C-H activation and hasreceived considerable attention over the past decades. Apart from aryl halides, avariety of coupling species, including organoboranes, aromatic carboxylic acids andarylsiloxanes are all frequently-used arylating agents. Here we propose a overall newroute: using sulfinic acid sodium salts as aryl source which are very stable to waterand air, palladium as a catalyst, sulfinic acid sodium salts via releasing SO2to couplewith indoles under relatively mild conditions. This type of reaction has a goodselectivity that the coupling reaction only occurs in the C2position.o-Amino phenols and their derivatives are often used for the preparation ofnitrogen and oxygen-containing heterocycles. However, amino is relatively notstable and easily to be oxidized. We have developed a2-arylbenzoxazoles formationreaction using o-nitrophenols and alcohols as starting materials which were cheap,available to be synthesized and relatively stable. Using iron as a green catalyst, werealized the nitro reduction, oxidation of alcohols, imine formation and cyclization in"one-pot", offering a new synthesis approach to2-arylbenzoxazoles environmentallyfriendly.