Heteroatom-Substituted Expanded Radialenes:  One-Pot Synthesis and Characterization of Expanded 1,3-Dithiolane[n]radialenes

The one-pot synthesis, crystal structure, and electronic absorption properties of expanded 1,3-dithiolan[5]radialene (6a), the first heteroatom-substituted expanded radialene molecule with dithiolanylidene groups as strongly donor termini, has been developed. Catalyzed by Ni(PPh₃)₂Cl₂−PdCl₂−CuI, radialene 6a was assembled by a highly efficient one-pot and protection-free oxidative coupling reaction of five α-enediyne units starting from the ready available α,α-diethynyl ketene dithioacetal (13) under mild conditions. The crystal of 6a, obtained by slow evaporation of DMSO and acetone solutions, shows that the inclusion complex of DMSO molecules in the cavity of radialene 6a molecule is formed. More importantly, owing to the introduction of the strong electron-donating alkylthio groups, per(alkylthiolated) expanded radialene 6a shows an extremely strong intramolecular push−pull interaction and enhanced macrocyclic cross-conjugation.