Cyclization of iminium ions for the generation of heterocycles: Total synthesis of (+/-)-deoxocassine and (+/-)-azimic acid and an approach to the homoerythrinane skeleton.

摘要

Iminium ions are important in organic synthesis because of their ease of formation and versatility. The use of several types of iminium ions is described. Starting from a furfurylamine moiety, a dihydropyridone template which can be used to generate N-sulfonyliminium ions is constructed via an aza-Achmatowicz reaction. The N-sulfonyliminium ions are explored as possible dipolar cycloaddition components and spectroscopic experiments are performed to probe possible reactivity. Additionally, the total synthesis of two natural products, (+/-)-deoxocassine and (+/-)-azimic acid is described from the same dihydropyridone scaffold. The key step of the two syntheses involves using an in situ generated N-sulfonyliminium ion to introduce the side chain of the natural product in stereoselective fashion. The single permutation of the side chain is then elaborated into the two natural products, highlighting the flexibility of this approach to alkaloids.; N-acyliminium ions also play an important role in organic synthesis. Herein we describe using a Pummerer reaction/N-acyliminium ion cyclization strategy to construct a hexahydroindolone framework. During this study, a new cyclization of the furan nucleus is discovered which shows that furan can function as a nucleophile in the 3-position, which is previously an unknown process. Combining the furan cyclization results with the tandem Pummerer/N-acyliminium method, the successful construction of the skeleton of the homoerythrinane alkaloid selaginoidine is described as well as a study which investigates the effect of ring size and nucleophilicity of furans.