Synthesis and structure of novel ferrocene-containing β-carbolines including polycondensed derivatives with the elements of planar-, central- and conformational chirality

Abstract

Employing tryptamine or tryptophane methylester hydrochloride and (Sp)-2-formylferrocene-1-carboxylate as precursors by means of Pictet–Spengler reactions and subsequent intramolecular acylation effected by cyanuricfluoride or carbonyldiimidazole (CDI), the first representatives of ferrocene-containing β-carboline derivatives including polycyclic ferroceno/fused lactames, were prepared. In the course of CDI-mediated tandem cyclization of a tryptophane-derived carboxyferrocenyl-substituted β-carboline, a ring enlargement simultaneously taking place with the loss of the η5-C5H5Fe+ fragment of the fused ferrocene moiety, effected by the coordinating imidazole released from the reagent, led to a 4H-cyclopenta[7,8]azonino[5,4-b]indole as a minor product. The constitution and relative configuration of the new compounds with the elements of planar-, central- and conformational chirality were established by NMR methods including HMQC, HMBC and NOESY measurements supported by DFT modeling studies.