Rhodium-Catalyzed Double Dearomatization of 1,2,3-Triazole–Isoxazole Dyads: Synthesis of Nonfused 1<i>H</i>-1,3-Diazepines

A double dearomatization of dyads consisting of 1-sulfonyl-1,2,3-triazoles and 3-aryl-5-methoxyisoxazoles was applied for the efficient synthesis of nonfused 1<i>H</i>-1,3-diazepines. The plausible mechanism of the cascade reaction includes transformation of the 1,2,3-triazole to rhodium azavinyl carbene, the <i>Z</i>-selective hydride shift to form the 1-azabuta-1,3-diene moiety, rhodium-catalyzed ring contraction of the isoxazole to azirine, and pseudopericyclic four-atom ring expansion of the azirine. The synthetic utility and antiproliferative activity of the 1,3-diazepines obtained have been demonstrated.