Ethyl Propiolate-Promoted Deaminative Coupling of Ferrocenylmethanamines with Carbon- and Heteronucleophiles: Stereospecific Access to Ferrocene-Peptide Conjugates.

The direct deaminative coupling of readily available ferrocenylmethanamines 1 with a range of carbon- and heteronucleophiles is achieved using ethyl propiolate as the sole activating reagent at room temperature. Enolizable carbon pronucleophiles can be used as the coupling partner directly without prior preactivation, presumably owing to in situ CH deprotonation promoted by the allegedly formed zwitterionic intermediate. α-Amino acid esters and derived di- and tripeptides also accommodated well as N-centered nucleophiles in the coupling with 1 without suffering detectable isomerization, thus providing a new stereospecific entry to ferrocene-peptide conjugates.