By developing a mild Ni-catalyzed system, a method for direct borylation of sp(2) and sp(3) C-N bonds has been established. The key to this hightly efficient C-N bond borylative cleavage depends on the appropriate choice of the nickel catalyst Ni(COD)2, ICy·HCl as a ligand, and the use of 2-ethoxyethanol as the cosolvent. This transformation shows good functional group compatibility and can serve as a powerful synthetic tool for gram-scale synthesis and late-stage C-N borylation of complex compounds.
Excising the nitrogen in secondary amines, and coupling the two residual fragments is a skeletal editing strategy that can be used to construct molecules with new skeletons, but which has been largely unexplored. Here we report a versatile method of N‐atom excision from N‐heterocycles. The process uses readily available N‐heterocycles as substrates, and proceeds by N‐sulfonylazidonation followed by the rearrangement of sulfamoyl azide intermediates, providing various cyclic products. Examples are provided of deletion of nitrogen from natural products, synthesis of chiral O‐heterocycles from commercially available chiral β‐amino alcohols, formal inert C−H functionalization through a sequence of N‐directed C−H functionalization and N‐atom deletion reactions in which the N‐atom can serve as a traceless directing group.
A versatile silver-promoted oxidative cascade reaction of N-aryl-3-alkylideneazetidines with carboxylic acids is reported, providing a very efficient pathway to functionalized fused pyridines. This method allows introduction of fused pyridine ring systems to heterocycles, drugs, and natural products. A mechanistic study revealed that silver salt is essential for the chemo- and regioselective ring expansion, sequential oxidative nucleophilic additions, and oxidative aromatization. This approach represents the first example of the strained N-heterocycles undergoing a cascade reaction with a π bond and a nucleophile together.
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