From 2- to 3-Substituted Ferrocene Carboxamides or How to Apply Halogen “Dance” to the Ferrocene Series

Abstract

Two methods were compared to convert ferrocene into N,N-diisopropylferrocenecarboxamide, N,N-diethylferrocenecarboxamide, N,N-dimethylferrocenecarboxamide, and (4-morpholinocarbonyl)ferrocene, namely, deprotometalation followed by trapping using dialkylcarbamoyl chlorides and amide formation from the intermediate carboxylic acid. The four ferrocenecarboxamides were functionalized at C2; in the case of the less hindered and more sensitive amides, recourse to a mixed lithium–zinc 2,2,6,6-tetramethylpiperidino-based base allowed us to achieve the reactions. Halogen migration using lithium amides was next optimized. Whereas it appeared impossible to isolate the less hindered 3-iodoferrocenecarboxamides, 3-iodo-N,N-diisopropylferrocenecarboxamide proved stable and was converted to new 1,3-disubstituted ferrocenes by Suzuki coupling or amide reduction. DFT calculations were used to rationalize the results obtained.