Nitrogen heterocycles. Part 6. Conversion of 3-(α-bromobenzylidene)-2-phenethylphthalimidine into pyrrole and benzazepine derivatives; base-catalysed rearrangement and photolysis of 3-(α-bromobenzylidene)phthalimidine

Abstract

3-Benzyl-3-hydroxy-2-phenethylphthalimidine (1) can be converted into (E)- and (Z)-3-benzylidene-2-phenethylphthalimidines, (2) and (3). Bromination of (2) and/or (3) affords a mixture of (Z)- and (E)-3-(α-bromobenzylidene)-2-phenethylphthalimidines, (4) and (5), in the ratio 67 : 33. The latter compounds cyclise on treatment with alkali to give a mixture of 7,8-dihydro-13-phenyl-5H-isoindolo[1,2-b][3]benzazepin-5-one (6), o-(3,4-diphenylpyrrol-2-yl)benzoic acid (7), and 1,2,3,9b-tetrahydro-1,2-diphenyl-5H-pyrrolo[2,1-a]isoindol-5-one (8). Photolysis of the phthalimidines (4) and (5) in methanol gives the isoindolobenzazepinone (6) only. When (Z)-3-(α-bromobenzylidene)phthalimidine (17) is treated with base in boiling ethylene glycol, conversion into 4-(β-hydroxyethoxy)-3-phenylisoquinolin-1 (2H)-one (18) takes place, and into the 4-[β-(β-hydroxyethoxy)ethoxy] derivative (20) when diethylene glycol is used as solvent. Photolysis of (17) in methanol leads to (Z)-3-(α-methoxybenzylidene)phthalimidine (22). In the light of the results obtained with the phthalimidine (17), the transformations promoted by the action of base seem to involve a carbenoid intermediate.