Fe(CO)5-catalyzed oxidative photolytic cyclization of ferrocenated en-yne-aldehydes: Synthesis of ferrocene appended furans

Abstract

En-yne-aldehydes are important organic motifs due to having a high synthetic potential of cyclization. Herein, the ferrocenated en-yne-aldehydes were successfully transformed into ferrocene appended furans by oxidative, photolytic exo-cyclic ring closure reaction in the presence of an earth-abundant metal catalyst, i.e., iron pentacarbonyl. Along with the formation of the furan ring, the carbon adjacent to furan gets oxidized into a carbonyl group. The transformation takes just 30 min to accomplish the desired product. The formation of these unusual ferrocene appended furan products were confirmed by single crystal X-Ray diffraction studies, FTIR, 1H & 13C NMR, and HRMS spectrometry. The general scope of the reaction was established and a library of 11 new ferrocene-appended furan products were developed. Here, the established reaction protocol was found to be active for aryl, alkyl, cycloalkyl, and ferrocenyl-substituted ene-yne-aldehydes and produced good to significant yield of the respective furan products. To the best of our minds, this report serves as the first example of iron-catalyzed photolytic oxidative cyclization of ferrocenated en-yne-aldehydes, and the products are first time reported in this report.