Photochemical approach to the synthesis of the pyrrolo[1,4]benzodiazepine antibiotics

The total syntheses of the pyrrolo (1,4)benzodiazepine antitumor antibiotics prothracarcin and DC-81 were realized using, as a key step, the photochemical (2 sigma + 2 pi ) ring expansion of the appropriately substituted N-pentenylphthalimide to afford the corresponding pyrrolobenzazepinedione. Conversion of the photoproduct into the antibiotic skeleton was effected by transformation of the benzylic ketone into a carbinolamine via a Curtius rearrangement sequence.