Scheme 2.1: Pinacol-pinacolone rearrangement of epinephrine to 3,4-dihydroxyphenylacetaldehyde.
3,4-dihydroxyphenylacetaldehyde (DOPAL),
which is not commercially available. We originally set out to synthesize the compound based on a paper by Kim (Kim 1996) that proposed the rearrangement in one step using perchloric acid in glacial acetic acid. Due to the risks associated with perchloric acid (can be explosive when heated), we sought out other means of synthesizing DOPAL.
In 1966, Robbins (Robbins 1966) synthesized a sodium bisulfite addition of DOPAL from epinephrine (adrenaline) using a phosphoric acid solution. Robbins based much of his work on a previously published paper by J. H. Fellman for which he proposed a pinacol-pinacolone type mechanism for the rearrangement of epinephrine (14) to DOPAL (15) in phosphoric acid (Fellman 1958) (Scheme 2.1).
Using the same procedure (Robbins 1966), we attempted to synthesize DOPAL (15) from commercially available epinephrine (adrenaline) (14).
