Ferrocenium hexafluorophosphate as an inexpensive, mild catalyst for the etherification of propargylic alcohols

• [Fe(Cp)2]PF6 catalyzes the etherification of propargylic alcohols (up to 90% yield).
• At mild temperatures (40 °C), the substrates are employed in equimolar amounts.
• Yield-diminishing rearrangement reactions are minimized under these conditions.

Commercial ferrocenium hexafluorophosphate ([FeCp2]PF6) was found to be an efficient catalyst for the etherification of terminal, tertiary propargylic alcohols with primary and secondary alcohols (5 h to 3 days reaction time at 40 °C in CH2Cl2, 3 mol% catalyst loading). The propargylic ether products were isolated in 90–20% yields. The alcohols and propargylic alcohols were employed in an equimolar amount and no further additives were required. For a purely aromatic propargylic alcohol, the isolated yields were lower than those for a mixed aromatic-aliphatic propargylic alcohol. Through monitoring reactant consumption and product formation over time, we found that the aromatic propargylic alcohol undergoes yield-diminishing Meyer–Schuster rearrangements to the aldehyde more easily than the mixed aromatic-aliphatic propargylic alcohol. The employment of [Fe(Cp)2]PF6 as a single electron oxidant has the potential to add a new direction in the development of catalysts for the title reaction based on single electron transfer processes.

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