Condensation of 3,6-dimethoxy-2-nitrobenzoyl chloride with L-proline methyl ester afforded amide 4, which underwent reductive cyclization with iron(II) sulfate and ammonium hydroxide to yield pyrrolobenzodiazepine 5. Oxidation of 5 with ammonium cerium(IV) nitrate led to the new heterocyclic quinone 6 in 53% overall yield.
Condensation of 3,6-dimethoxy-2-nitrobenzoyl chloride with L-proline methyl ester afforded amide 4, which underwent reductive cyclization with iron(II) sulfate and ammonium hydroxide to yield pyrrolobenzodiazepine 5. Oxidation of 5 with ammonium cerium(IV) nitrate led to the new heterocyclic quinone 6 in 53% overall yield.