Folded conformations due to arene interactions in dissymmetric and symmetric butylidene-linker models based on pyrazolo[3,4-d]pyrimidine, purine and 7-deazapurine

The butylidene-linker models 1-[2-(2,6-dimethylsulfanyl-9H-purin-9-yl)-2-methylidenepropyl]-4,6-bis(methylsulfanyl)-1H-pyrazolo[3,4-d]pyrimidine, C18H20N8S4, (XI), 7,7'-(2-methyl-idenepropane-1,3-diyl)bis[3-methyl-2-methylsulfanyl-3H-pyrrolo[2,3-d] pyrimidin-4(7H)-one], C20H22N6O2S2, (XIV), and 7-[2-(4,6-dimethylsulfanyl-1H-pyrazolo[3,4-d] pyrimidin-1-yl)-2-methylidenepropyl]-3-methyl-2-methylsulfanyl-3H-pyrrolo[2,3-d] pyrimidin-4(7H)-one, C19H21N7OS3, (XV), show folded conformations in solution, as shown by H-1 NMR analysis. This folding carries over to the crystalline state. Intramolecular pi-pi interactions are observed in all three compounds, but only (XIV) shows additional intramolecular C-H center dot center dot center dot pi interactions in the solid state. As far as can be established, this is the first report incorporating the pyrrolo[2,3-d] pyrimidine nucleus for such a study. In addition to the pi-pi interactions, the crystal structures are also stabilized by other weak intermolecular C-H center dot center dot center dot S/N/O and/or S center dot center dot center dot N/S interactions.