Catalyst-free [3 + 2] cyclization of dihydroisoquinoline imines and isatin-derived Morita-Baylis-Hillman carbonates via 1,5-electrocyclization: synthesis of tetrahydroisoquinoline-fused spirooxindoles.

We have developed a mild and scalable catalyst-free [3 + 2] cyclization of dihydroisoquinolines and isatin-derived Morita-Baylis-Hillman carbonates. The incorporation of tetrahydroisoquinoline and spirooxindole frameworks could be realized affording highly functionalized heterocycles in moderate to excellent yields with good diastereocontrols (up to 92% yields, >20 : 1 dr). The extension of this method to dihydro-β-carbolines has also been achieved. A gram-scale reaction could be performed successfully enabling the potential application for further biomedical research.