Synthetic Approaches to the Quinolinequinone System of Streptonigrin

Model studies directed toward synthesis of the quinolinequinone AB ring system of streptonigrin (1) using approaches based upon Friedlander quinoline synthesis are described. Aldehyde 6 has been prepared from o-vanillin, and several unsuccessful attempts were made to convert it to the model quinolinequinone 36. A successful route to 36 was developed using the o-aminobenzaldehyde 30. Friedlander condensation of 30 with 2-acetylpyridine produced quinoline 31, which can be transformed in a few simple steps to quinolinequinone 36. This last route should be applicable to a total synthesis of streptonigrin.