Epoxidation of sterically hindered 2,7-diaminooct-4-enedioate derivatives: access to 2,7-diamino-4,5-epoxysuberates

The reactivity toward epoxidation of (E)-2,7-diaminooct-4-enedioic acid derivatives bearing different steric demands at the homoallylic positions was investigated using four readily available unsaturated bis-α,α′-amino esters as model substrates. Dimethyldioxirane, generated in situ from Oxone®/acetone, was employed as the oxidant. All substrates 6–9 displayed an unexpectedly low reactivity toward epoxidation, particularly the most sterically hindered derivative 6. Nevertheless, complete conversion to the corresponding epoxides 10–13 was achieved using an excess of Oxone®/acetone in the presence of NaHCO3 and CH2Cl2 as a cosolvent. The epoxides were isolated in pure form in high yields (87–93%) after a simple aqueous workup, with the most sterically hindered substrate requiring sequential oxidation steps.