Ferrocene Templated Synthesis of Fused Aminofulvenes: Elaboration of Chalaniline A and a Reversed Regioisomer via a Ferroceno[b]chromone

Ferrocenes were studied as cyclopentadiene ring surrogates enroute to non-metallocene targets such as the aminofulveno[1,2-b]chromone natural product chalaniline A. Ferroceno[b]chromone, as an archetype of interest, was prepared from ferrocenecarboxylic acid (4 steps, 24% yield) via N,N-diethyl 2-iodoferrocenecarboxamide by Ullmann etherification with phenol followed by LDA mediated anionic cyclization. Reactivity studies revealed that this planar chiral analogue of xanthone readily fragments into non-metallocene products upon reaction with electrophiles. 1-Methoxy-3-methylferroceno[b]chromone, prepared similarly by substituting O-methylorcinol for phenol, was advanced to chalaniline A and a transposed regioisomer by concomitant deferration and demethylation with AlCl3, formylation of the resulting cyclopentadiene fused chromone with excess Vilsmeier reagent, and then Pinnick oxidation (NaClO2), methylation (TMSCHN2), and final transamination (PhNH2). Four compounds, including ferroceno[b]chromone and the C11/C12 transposed regioisomer of chalaniline A, were characterized by single crystal X-ray diffraction analysis.

Publikationsverlauf

Eingereicht: 11. Juli 2025

Angenommen nach Revision: 18. August 2025

Accepted Manuscript online:
18. August 2025