New methodology for the preparation of 3-hydroxy-2-pyridinone (3,2-HOPO) chelators and extractants. Part 2: Reactions of alcohols, phenols, and thiols with an electrophilic 3,2-HOPO reagent

The alkylation of mesylate salt 1 with alcohols, phenols, and their sulfur analogs provides a convenient method for the synthesis of a variety of HOPO derivatives. The reactions of the electrophilic iminium ester mesylate salt 1 with alcohols, phenols, and thiols have been investigated. In the presence of base, thiols, phenols, and thiophenol react with 1 to give the corresponding ether linked HOPO derivatives in good yields. However, the ring opening of salt 1 with alcohols could only be accomplished efficiently using a large excess of the alcohol in the presence of methanesulfonic acid at 80 °C. The synthetic utility of HOPO precursor, 1, has been demonstrated by the synthesis of two polyHOPO chelators 7 and 9.