Propargylic alcohols are valuable starting materials in the synthesis of organic molecules. The transformation of propargylic alcohols opens a pathway to a variety of synthetic targets. Due to the close proximity of an alcohol and an alkyne unit in propargylic alcohols, their reaction landscape is complex. Rearrangements of propargylic alcohols are common and can decrease yields in their transformation but catalysis is a way to minimize those yield-diminishing side reactions. Catalysts for propargylic substitution reactions are known, and are mainly based on ruthenium. Iron is an attractive metal for catalysis, as it is inexpensive and non-toxic. The application of iron catalysts in the transformation of propargylic alcohols is, by far, not as well established as catalysts based on other transition metals. The presentation will demonstrate new applications of ruthenium- and iron-based catalysts for the catalytic transformation of propargylic alcohols. We determined that ferrocenium ions [Fc]+ are catalytically active in the etherification of propargylic alcohols utilizing alcohols as the nucleophiles. The reaction temperatures of 40 °C for these reactions are lower than those of cationic ruthenium complexes that were previously synthesized in our group to catalyze the same reactions. The low reaction temperature may point towards a difference in mechanism compared to our previously investigated, ruthenium-catalyzed substitution reactions. Cationic intermediates are often postulated for substitution reactions of the –OH unit in propargylic alcohols by nucleophiles. However, ferrocenium cations are 17 valence electron complexes and can act as one electron oxidants, triggering radical chemistry. The ferrocenium catalyzed activation might consequently proceed through radical chemistry or through single electron transfer processes. The presentation will discuss the mechanistic pathways that the reaction may proceed through and our investigations to elucidate a reaction mechanism.

Cationic ferrocenium salts for the catalytic activation of propargylic alcohols

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.