Elaboration of the Pyridine C-Ring Functionality in a Streptonigrin Precursor

Model studies directed toward total synthesis of streptonigrin (1) are outlined. A number of attempts to introduce a 3-amino substituent into compounds 6 and 18, prepared previously by Diels-Alder reactions, are described. A successful method for introduction of this substituent into a preformed pyridine via introduction of a functionalized carbon followed by Curtius rearrangement has been developed. Compound 52 has been prepared which contains all of the features present in the pyridine C ring of streptonigrin synthon 3.