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

Abstract

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 (5h to 3 days reaction time at 40°C in CH2Cl2, 3mol% 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.