The development of sustainable strategies for the synthesis of highly functionalized N-containing heterocycles is of great importance for the preparation of pharmaceuticals, agrochemicals and functional materials. Thus, the focus of the present work was set on the construction of a variety of heterocyclic frameworks through palladium-catalyzed or metal-free direct C−H functionalizations. At first, the substrate scope for the direct C–H alkynylation of oxazoles with gem-dichloroalkenes was explored. Subsequeutly, diaryliodonium tosylates were used for metal-free C2-arylations of indoles bearing the acetamide functionality at the C3 position. Meanwhile, the challenging metal-free arylation-cyclization cascade reaction was elaborated by blocking the C2 position of indoles, delivering C3-aryl pyrroloindolones. Thereafter, The approach for the metal-free C−H arylations of indoles was further applied to peptides involving the indolylacetyl moiety as a tag at the N-terminus. Finally, The late-stage modification of tryptophan-containing peptides was accomplished through the palladium-catalyzed C–H arylation.
Keywords: direct C−H functionalization; alkynylation of oxazoles; arylation of indoles; late-stage arylation of tryptophan-containing peptides; metal-free synthesis of pyrroloindolones
