Aryl Boron Compounds as Linchpins for the Modular Construction of Benzo-Fused Seven-Membered N,O-Heterocycles from Nonphenolic Arenes

Abstract

Saturated seven-membered N-heterocycles are underrepresented among approved pharmaceuticals, partly because reliable methods to construct them on complex aromatic cores remain scarce. We recently reported a rhodium-catalyzed C(sp2)–H amination protocol that delivers tetrahydro-1,5-benzoxazepines from phenols, but the requirement for a preexisting phenolic handle restricted the approach to phenol-bearing substrates. Here, we lift this constraint by using aryl boron compounds as entry points to the same cyclization manifold. Three complementary approaches provide an aryl boron compound that serves as a linchpin, whose position on the arene defines that of the resulting phenol after oxidation. These approaches include iridium-catalyzed C–H borylation, electrophilic halogenation followed by Miyaura borylation, and the direct use of a preformed aryl boron reagent. The installed boron linchpin is elaborated to an O-benzoylhydroxylamine precursor and cyclized by rhodium-catalyzed intramolecular C(sp2)–H amination. The sequence provides modular access to benzo-fused seven-membered N,O-heterocycles from pharmaceuticals, π-extended functional materials, amino acid derivatives, and heterocyclic scaffolds whose corresponding phenols are not readily available. A tryptophan example demonstrates the regiocomplementarity of the aryl-boron entry to the phenol-anchored route, while unsuccessful substrates delineate oxidation-sensitive heteroarenes and substrate-dependent linker cleavage as the current limitations of the method.