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Potassium phthalimide is used as an intermediate in the synthesis of N-alkylated phthalimides, which is involved in the preparation of primary amines (Gabriel synthesis) by the hydrolysis reaction. It is also used as an intermediate for synthetic indigo, pigments, dyes and pharmaceuticals. Further, it is employed as an organocatalyst for the cyanosilylation of various carbonyl compounds under extremely mild conditions. In addition to this, it serves as a reagent for the transformation of allyl- and alkyl halides into protected primary amines.
For an example of the classical Gabriel synthesis of primary amines from an alkyl halide by alkylation of potassium phthalimide followed by hydrolysis, see: Org. Synth. Coll., 2, 25 (1943). For use of the Gabriel reaction on Merrifield resin as the first step of a synthesis of a polymer-supported carbodiimide, see: Org. Synth. Coll., 6, 951 (1988). The phthalimide alkylation is often carried out in DMF. A liquid-liquid phase-transfer method using (n-Hexadecyl)tri-n-butylphosphonium bromide, L01335, as catalyst also gives excellent results: Synthesis, 389 (1976).
The standard method for cleavage of the N-substituted phthalimide is with hydrazine hydrate, effective under milder conditions than acid or base hydrolysis. Other hydrazines and primary amines have also been successful, e.g. methylhydrazine or N,N-dimethylpropanediamine: Org. Synth. Coll., 9, 13, 16 (1998). Another technique involves borohydride reduction to the hydroxy amide, and liberation of the amine with acetic acid, with cyclization to phthalide: Tetrahedron Lett., 25, 2093 (1984). For suggested improvements to the cleavage conditions in the Gabriel synthesis, see: J. Org. Chem., 61, 8063 (1996). Review of the Gabriel reaction: Angew. Chem. Int. Ed., 7, 919 (1968).
For an alternative approach to the formation of primary amines, see Dibenzylamine, A11554.
Kiyokawa, K.; Kosaka, T.; Kojima, T.; Minakata, S. Synthesis and Structure of Hypervalent Iodine(III) Reagents Containing Phthalimidate and Application to Oxidative Amination Reactions. Angew. Chem. Int. Ed. 2015, 127 (46), 13923-13927.
Fesenko, A. A.; Trafimova, L. A.; Albov, D. V.; Shutalev, A. D. Nucleophile-dependent diastereoselectivity in the ring expansion of pyrimidines to give 1,3-diazepines. Tetrahedron Lett. 2015, 56 (11), 1317-1321.