Access to Electron-Rich Arene-Fused Hexahydroquinolizinones through a Gold-Catalysis-Initiated Cascade Process

摘要

We have recently developed a two-step, one-pot synthesis of piperidine-4-ols. In this reaction, the protonated cyclic imidate intermediate A, which is prepared by a gold-catalyzed amide cyclization, is reduced by an external hydride (e.g., catecholborane), which initiates a key Ferrier rearrangement (Scheme 1 a). We envisioned that a carbon nucleophile could replace the hydride in this chemistry; moreover, if such a nucleophile is attached to the amide nitrogen atom, addition of reagent in the course of the reaction is not needed. The reaction would constitute a gold-catalysis-initiated cascade process and might provide an efficient access to bicyclic piperidin-4-ones (e.g., 1, Scheme lb). Herein, we disclose our implementation of this strategy, which leads to an expedient synthesis of electron-rich arene-fused hexahydroquinolizinones; its synthetic utility is illustrated by a succinct and stereoselective synthesis of dihydrocorynantheol without the use of any protecting group, and a formal synthesis of yohimbine and β-yohimbine.