摘要
Three-membered unsaturated rings have been widely utilized in organic synthesis due to their inherent highly strained structures.Although much research has been applied to ring-expansion reactions of such strained ring systems,pathways other than[3+2]cycloadditions have rarely been observed in their reactions with alkynes,and to date,no[3+1]cycloadditions of isolated three-membered unsaturated rings with alkynes have been reported.Here we demonstrate an unprecedented[3+1]cycloaddition in which a fused metalla-azirine is used as a template to generate a series of planar CCCCX-type(X=N,O,S)pentadentate carbolong complexes 3–6.A series of substituted alkynes was tested for further exploration of the scope and mechanism for the[3+1]cycloaddition reactions.Complexes 3–6 represent rare examples of planar pentadentate complexes that assemble fourπ-conjugated fused rings by one bridgehead atom.These novel complexes are thermally stable in air and absorb ultraviolet,visible,and near-infrared light,and thus are potentially applicable in photoelectric devices and pharmaceuticals.
基金
supported by the National Natural Science Foundation of China(U1705254,21871225,and 21931002)
the Fundamental Research Funds for the Central Universities(20720190042),and the Research Grants Council of Hong Kong(N_HKUST603/15).
