Unusual molecular conformation in dissymmetric propylene-linker compounds containing pyrazolo[3,4-d]pyrimidine and phthalimide moieties

The crystal structure of 4,6-bis(methylsulfanyl)-1-phthalimido-propyl-1H-pyrazolo[3,4-d] pyrimidine, C18H17N5O2S2, (VI), reveals an unusual folded conformation due to an apparent intramolecular C - H ... pi interaction between the 6-methyl-sulfanyl and phenyl groups. However, the closely related compound 6-methylsulfanyl-1-phthalimidopropyl-4-(pyrrolidin-1-yl)-1H-pyrazolo[3,4-d]pyrimidine, C21H22N6O2S, (VII), exhibits a fully extended structure, devoid of any intramolecular C - H ... pi or pi - pi interactions. The crystal packing of both molecules involves intermolecular stacking interactions due to aromatic pi - pi interactions. In addition, (VI) exhibits intermolecular C - H ... O hydrogen bonding and (VII) exhibits dimerization of the molecules through intermolecular C - H ... N hydrogen bonding.