Concise Enantioselective Total Syntheses of (+)‐Homochelidonine, (+)‐Chelamidine, (+)‐Chelidonine, (+)‐Chelamine and (+)‐Norchelidonine by a Pd II ‐Catalyzed Ring‐Opening Strategy

New enantioselective syntheses of the B/C hexahydrobenzo[ c ]phenanthridine alkaloids (+)‐homochelidonine, (+)‐chelamidine, (+)‐chelidonine, (+)‐chelamine, and (+)‐norchelidonine are described. Our rapid and convergent route to this class of natural products involved the development and application of a Pd II ‐catalyzed asymmetric ring‐opening reaction of a meso ‐azabicyclic alkene with an aryl boronic acid as the key step. By screening a variety of functionalized ortho ‐substituted aryl boronic acids, chiral ligands and reaction conditions we were able to prepare the requisite cis ‐1‐amino‐2‐aryldihydronaphthalenes in high yield and in up to 90 % ee . Early attempts to complete the synthesis of (+)‐homochelidonine using an N ‐Boc azabicyclic alkene are described in full. The successful route required a protecting group alteration followed by B ring formation and then stereoselective installation of the C‐11 syn‐ hydroxy group by regioselective epoxide ring‐opening using a hydride source. Ring‐opening of the same epoxide intermediate with water ultimately led to the synthesis of (+)‐chelamidine. The same strategy was then used to synthesize the other structurally similar B/C hexahydrobenzo[ c ]phenanthridine alkaloids, (+)‐chelidonine, (+)‐chelamidine, and (+)‐norchelidonine.