Reduction of 4-aza- and 5-azaphthalimides with Zn dust in acetic acid resulted in two distinct outcomes: i) in the 4-aza series, the reduction process stopped at the stage of 3-hydroxy-4-azaisoindolin-1- ones (isolated in 69-90% yield), presumably, stabilized by an intramolecular hydrogen bond; more forcing condition (110, 2 days) are required to obtain 4-azaisoindolin-1-ones; ii) in the 5-aza series, even at low temperatures (∼10), overreduction could not be avoided; practical yields of 4-azaisoindolin-1-ones (59- 85%) were achieved using elevated temperatures (50°C). The method described offers a practical alternative to hitherto reported sodium borohydride reduction of 4-azaphthalimides, which suffers from poor selectivity and isolated yields. Reductive manipulation of 5-azaphthalimides was studied for the first time.
Keywords: Azaphthalimides, chemoselective reduction, isoindolones, intramolecular hydrogen bond, combinatorial compound libraries
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