A novel 3,4-dihydroisoquinoline annulation: expedient access to isoquinoline heterocycles

3,4-Dihydroisoquinoline carboxylate undergoes a smooth annulation with ω-bromopropionate, butyrate or ortho-bromomethyl benzoate to afford the isoquinoline heterocycle upon treatment with potassium tert-butoxide in DMF at −60 °C. This novel annulation constitutes a formal direct synthesis of cyclic Reissert equivalent compounds, thus offers an expedient access towards certain medicinally important isoquinoline heterocycles and relevant natural alkaloids, that is, of berberine and erythrina types.