An Improved Synthesis of Natural Product Inspired Chromenopyrrolizines and Chromenoindolizines Scaffolds: Rapid Access to the Diverse Pyrrolizine Analogs of Aza-Medicarpin and Tetracyclic Isolamellarin Core through a General Base and Metal Free Strategy

摘要

An improved synthesis for easy access to the natural product inspired chromenopyrrolizine and chromenoindolizine scaffolds is delineated. The strategy involves controlled thermal activation of diverse salicylaldehyde tethered dipolarophiles having the strategically stationed activating substituents with proline/pipecolic acid for the facile [3+2] cycloaddition of the in situ generated azomethine ylides and concomitant oxidation of the resulting cycloadducts to arrive at diverse chromenopyrrolizine or pyrrolizine analogs of aza-medicarpin and chromenoindolizines embodying the tetracyclic core isomeric to lamellarin alkaloids, in good yields under base and metal free condition.