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Two efficient iodine-mediated strategies, which are economical and one-pot, are described to access bis(imidazo[1,2-a]pyridin-3-yl)sulfanes and bis(imidazo[1,2-a]pyridin-3-yl)disulfanes in chloroform and acetic acid, respectively, by a direct oxidative homocoupling of imidazo-heterocycles using inexpensive sodium sulfide as a sulfur source. These strategies are scalable, and an array of substrates delivered their corresponding stable sulfur-bridged imidazo-heterocycles in excellent yields.

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A direct ortho‐Csp2‐H acylmethylation of 2‐aryl‐2,3‐dihydrophthalazine‐1,4‐diones with α‐carbonyl sulfoxonium ylides is achieved through a RuII‐catalyzed C−H bond activation process. The protocol featured high functional group tolerance on the two substrates, including aryl‐, heteroaryl‐, and alkyl‐substituted α‐carbonyl sulfoxonium ylides. Thereafter, 2‐(ortho‐acylmethylaryl)‐2,3‐dihydrophthalazine‐1,4‐diones were used as potential starting materials for the expeditious synthesis of 6‐arylphthalazino[2,3‐a]cinnoline‐8,13‐diones and 5‐acyl‐5,6‐dihydrophthalazino[2,3‐a]cinnoline‐8,13‐diones under Lawesson's reagent and BF3⋅OEt2 mediated conditions, respectively. Of these, the BF3⋅OEt2‐mediated cyclization proceeded in DMSO as a solvent and a methylene source via dual C−C and C−N bond formations.

A Rh(III)-catalyzed strategy involving the [4+1] annulation of 2-arylphthalazine-1,4-diones with α-diazo carbonyl compounds was developed, accessing a series of unprecedented hydroxy-dihydroindazolo-fused phthalazines in good to excellent yields. By varying the additive, phthalazino-fused cinnolines were synthesized under Rh-catalyzed conditions via [4+2] annulation between the same starting materials. Notably, such two strategies showed a good functional group tolerance and high atom efficiency.