Enantioselective Synthesis of the Diazatricyclic Core of Alkaloid TAN1251C via an Iodoaminocyclization Reaction

A concise enantioselective synthesis of the diazatricyclic core of alkaloid TAN1251C is reported. The method featured a stereoselective formation of the iodide intermediate 16b (in 2:1 ratio) from homoallylic amine 11b by iodine‐promoted iodoaminocyclization, a previously claimed to be unsuccessful reaction. The intermediate 16b was converted to the tricyclic core of TAN1251C 28 in five steps. During this study, two unexpected products 22 and 25 were obtained, and compound 23, derived from 11a was shown to be unsuitable for the oxidative formation of the enamide of TAN1251C. I2‐promoted intramolecular iodoaminocyclizations of homoallylamine (11b), followed by amination and deprotection of O‐TBS afforded the 1‐azaspiro[4,5]decane compound 18b. 18b was subjected to debenzylation and oxidation, followed by treatment with K2CO3, MeOH/H2O to provide the diazatricyclic core structure (28) of the alkaloid TAN1251C.