Unified Total Synthesis of C ₂ -Symmetric Bis(cyclotryptamine) Alkaloids Utilizing a Single-Atom Insertion/Deletion Strategy

Strategies for total synthesis have advanced alongside the development of new methodologies, thereby enabling access to structurally intricate molecules that were previously difficult to obtain. Here, we present a strategy for the synthesis of bis(cyclotryptamine) alkaloids inspired by methods for single-atom insertion/deletion. To implement our plan, we first pursued the synthesis of tetrahydropsychotriadine (4), an isomer of calycanthine (1), which was achieved in 9 steps and set the stage for the preparation of calycanthine (1), chimonanthine (2), and psychotriadine (6). Our studies, driven by calculations, also provide the first access to a natural product bearing the pyrrolidinoquinoline scaffold, CPC-2 (29). Finally, we resolve a long-standing misassignment of the structure of the natural product dubbed isocalycanthine. En route to our synthesis of 4, we establish a methodology for the construction of unprecedented diaryl-substituted cis- and trans-fused 5,5-bicycles using a photodecarbonylation. The mechanism for the trans-selective formation of 5,5-bicycles is investigated by using DFT calculations.