Catalyst‐Free Synthesis of Novel Dimeric Tetrahydroisoquinoline Derivatives through [2+2+2] Annulation

A simple, straightforward, and atom economic catalyst‐free [2+2+2] annulation of dihydroisoquinolines and allenoates has been developed. A diverse range of novel dimeric tetrahydroisoquinoline derivatives can be prepared in moderate to good yields (37–87 %) from readily available material. Dihydro‐β‐carboline can also be used in this reaction system delivering corresponding dimeric dihydro‐β‐carboline derivatives. Notably, the reaction could be easily scaled up to gram scale. The easy scale‐up of this process may provide structurally diversified natural product‐like molecules possessing privileged scaffold for potential application in biomedical research and other research fields. Interestingly, in contrast to the α,β‐selectivity observed in our previous study, β,γ‐selective [2+2+2] annulation was preferred in this work.