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

The primary amino group of 3‐(2‐aminoethyl)‐3‐(4‐chlorophenyl)‐2,3‐dihydro‐1H‐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(3H)‐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(3H) ‐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).