Isoindole-4,7-diones, synthesis

An ingenious synthesis of 1-arylisoindolcs has been developed by Vebor and Lwowski, based upon the reaction of an o-phthalimido-methylbenzophenone (41, R = aryl) with hydrazine (Table IV). The benzophenone is prepared by a Friedel-Crafts reaction with o-phthalimidomethylbenzoyl chloride (40). The mechanism of isoindole formation can be represented sehematically by a sequence involving attack by hydrazine at the imide to give the ring-opened hj drazide (42), followed by cyclization to phthalazine-l,4-dione (44) with displacement of the o-aminomethylbenzophenone (43). Intramolecular condensation of the latter can lead, via the isoindolenine... 

Thus, as shown in Scheme 10.2, in the Gabriel synthesis," the anion of phthalimide [1,2-benzenedicarboximide or lH-isoindole-l,3(2H)-dione] generated by treatment of the imide with sodium ethoxide (Na" OCH2CH3) in ethanol (CH3CH2OH) is... 

Scheme 10.2. The Gabriel synthesis using bromoethane (CH3CH2Br) on reaction with phthalimide [1,2-benzenedicarboxunide or lH-isoindole-l,3(2H)-dione] in the presence of base to produce ethanamine. The solvent is shown as dimethylformamide (DMF).

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