The synthesis of 1‐alkyl‐4a‐(4‐chlorophenyl)‐ 4,4a‐dihydropyrimido[6,1‐ a] isoindol‐9(3 H )‐one

The primary amino group of 3‐(2‐aminoethyl)‐3‐(4‐chlorophenyl)‐2,3‐dihydro‐1 H ‐isoindol‐1‐one ( 1 ) was acylated with acetyl chloride, benzoyl chloride and phenyl acetyl chloride to form the amides 2a ‐c, respectively. These were cyclized in phosphorus oxychloride to give the 1‐substituted‐4a‐(4‐chlorophenyl)‐4,4a‐dihydropyrimido [6,1‐ a ]isoindol‐9(3 H )‐ones 3a‐c . Heating of 1 in formic acid lead to the formation of 4a‐(4‐chlorophenyl)‐4,4a‐dihydropyrimido[6,1‐ a ]isoindol‐9(3 H ) ‐one (3d) . Heating of 1 in the presence of phosgene lead to the formation of 4a‐(4‐chlorophenyl)‐2,3,4,4a‐tetrahydropyrimido[6,1‐ a ]isoindole‐1, 9‐dione (4).