Synthesis and chemical reactivity of indenoisoxazoles

Treatment of 2‐pivaloyl‐1,3‐indandione (1) with hydroxylamine under acidic conditions, results in formation of 8‐t‐butylindeno[1,2‐c]isoxazol‐7‐one (2) while treatment of the triketone with hydroxylamine at neutral or basic pH gave 6 which upon cyclization gave the isomeric 3‐t‐butylindeno[1,2‐c]isoxazol‐4‐one (7). Compound 7 was readily reduced to amine 12 by treatment with hydrazine or hydrogen over platinum. The amine, although quite unreactive, was converted to 3‐t‐butylindeno[1,2‐c]pyrazol‐4‐one (13) with hydrazine or reduced to 15 and 16 with sodium in liquid ammonia and alcohol. Surprisingly, the amine 3 obtained from isoxazole 2 gave reduction product 15 from a sodium‐liquid ammonia reduction and not the expected product 18. Spectral evidence for each of the structures is discussed.