Brønsted Acid Triggers [6/7 + 1] Cascade Cyclization by N-Alkyl Amine C(sp³)–N Cleavage: Mild Synthesis of Benzo[1,4]oxazepane and Dihydrobenzo[1,5]oxazocine

Abstract

A catalyst-free mild synthesis was reported to produce medium-ring oxazepane and oxazocine derivatives from aminomaleimides and N-alkyl amines. The substrate and acidic additives were employed to cleave the C(sp 3 )−N bond as a onecarbon synthon for C−C and C−O coupling, thus facilitating the [n + 1] cascade cyclization reaction, which enabled the construction of seven-and eight-membered N,O-heterocycles at room temperature. The method exhibits abroad substrate scope and remarkable tolerance toward various functional groups (seven-membered 28 examples, eight-membered 8 examples, and activated Nalkyl amine 12 examples) and utilization of natural products (2 examples).