Studies toward Total Synthesis of (±)-Caldaphnidine C via One-Pot Sequential Intramolecular Vilsmeier-Haack and Azomethine Ylide 1,3-Dipolar Cycloaddition

An application of a one-pot sequential Vilsmeier-Haack cyclization and intramolecular azomethine ylide 1,3-dipolar cycloaddition toward the total synthesis: of (+/-)-caldaphnidine C is presented. It allowed an efficient formation of three cycles with perfect control of four of the five newly created stereogenic centers including one, all-carbon quaternary center. Two synthetic strategies to produce the key-step precursor, the investigation and optimization of the cyclization partners (nucleophile, azomethine ylide, and dipolarophile), and further derivatization of the cycloadduct are reported.