An oxidative cyclization of 1‐(2‐aminophenyl)pyrrole with styrenes has been developed for the synthesis of pyrrolo[1, 2‐a]quinoxaline derivatives using I2/2‐iodoxybenzoic acid (IBX) in DMSO as an effective oxidant. I2 is found to catalyze effectively the oxidative cyclization of phenylacetylene and ethyl benzoylacetate with 1‐(2‐aminophenyl)pyrrole even in the absence of IBX to generate pyrrolo[1, 2‐a]quinoxaline derivatives under metal‐free conditions.
We propose the synthesis of biologically relevant hexahydro‐1H‐pyrano[3,4‐c]chromenes, via a tandem Prins/Friedels‐Crafts process, catalyzed by BF3.Et2O, starting from (E)‐ and (Z)‐5‐phenoxypent‐3‐en‐1‐ol. The diastereoselectivity of the process is controlled by the geometry of the homoallylic alcohol. We also point out that the Prins product can be obtained in high yields and good diastereoselectivity when the reaction is promoted by AlCl3 as Lewis acid in the presence of an external nucleophile.
A facile and concise synthesis of β-carboline alkaloids, such as (–)-isocyclocapitelline and (+)-cyclocapitelline, has been achieved from commercially available geraniol through a unified strategy. The key steps involved in this synthesis are Sharpless epoxidation, intramolecular ring opening of epoxide, Pictet-Spengler reaction, and dehydrogenative aromatization using 10% palladium/carbon in xylene under neutral conditions.
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