Synthesis of phthalimides. An efficient and simple method enables the N-alkylation of aromatic cyclic imides using cesium carbonate as the base in anhydrous N,N-dimethylformamide at low temperatures (20-70˚C).The method is compatible with base labile functional groups.

The Gabriel Synthesis Uses A “Protected” Amine (Phthalimide) In An SN2 Reaction That Does Not Undergo Over-Alkylation. ... In phthalimide, a nitrogen is flanked by two carbonyl groups. This means that the N-H is a lot more acidic than it normally would be, because the resulting anion will be resonance stabilized.

Potassium phthalimide is a -NH2-synthon which allows the preparation of primary amines by reaction with alkyl halides. After alkylation, the phthalimid is not nucleophile and does not react anymore. Product is cleaved by reaction with base or hydrazine, which leads to a stable cyclic product.

The Gabriel method generally doesn't work with secondary alkyl halides. Another disadvantage of this synthesis is that using acidic/basic hydrolysis gives a low yield whereas the usage of hydrazine can make the conditions of the synthesis relatively harsh.

PHTHALAMIDE FOR SYNTHESIS