Lewis acid-catalyzed domino inverse electron-demand Diels–Alder \/ thermal ring expansion reaction for the synthesis of arene-annulated eight-membered nitrogen heterocycles

A domino inverse electron-demand Diels–Alder reaction/thermal ring expansion sequence was developed to enable the one-step synthesis of arene-annulated eight-membered nitrogen heterocycles from readily available aromatic 1,2-diazines. A boron-based, bidentate Lewis acid catalyst facilitates the initial cycloaddition of Boc-protected 2-azetine with various electron-poor and electron-rich phthalazines. The subsequent electrocyclic ring expansion furnishes azocines fused to differently substituted aromatics, a structural motif that holds vast potential for further derivatization.