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-methylidenepropane-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 (1)H NMR analysis. This folding carries over to the crystalline state. Intramolecular π-π interactions are observed in all three compounds, but only (XIV) shows additional intramolecular C-H···π 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 π-π interactions, the crystal structures are also stabilized by other weak intermolecular C-H···S/N/O and/or S···N/S interactions.

Pyrazolo[3,4-d]pyrimidinophanes: convenient synthesis of a new class of cyclophane and X-ray structure of the first representative.

A convenient synthesis of a new class of novel pyrazolo[3,4-d]pyrimidinophanes (four products, 41%), a new class of cyclophane, and X-ray structure of the first dissymmetrical [3.4]pyrazolo[3,4-d]pyrimidinophane (22%) are reported for the first time. The conformation of major syn product 6b is stabilized by weak pi-pi and O...Ar interactions.

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-phthalimidopropyl-1H-pyrazolo[3,4-d]pyrimidine, C(18)H(17)N(5)O(2)S(2), (VI), reveals an unusual folded conformation due to an apparent intramolecular C-H.pi interaction between the 6-methylsulfanyl and phenyl groups. However, the closely related compound 6-methylsulfanyl-1-phthalimidopropyl-4-(pyrrolidin-1-yl)-1H-pyrazolo[3,4-d]pyrimidine, C(21)H(22)N(6)O(2)S, (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.

4,6-bis(methylsulfanyl)-1-(4-phenoxybutyl)-1H-pyrazolo[3,4-d]pyrimidine.

The molecular structure of the title compound, C(17)H(20)N(4)OS(2), does not show any intramolecular aromatic pi-pi interactions, but the crystal packing reveals the presence of intermolecular C--H...O and C-H...pi interactions. The C--H...O interactions generate chains of molecules that are linked into sheets by C-H.pi interactions about inversion centres.

A stacked pyrazolo[3,4-d]pyrimidine-based flexible molecule: the effect on stacking of a bulky isopropyl group in comparison with a methyl/ethyl group.

In the crystal structure of 1,3-bis(4,6-diisopropylsulfanyl-1H-pyrazolo[3,4-d]pyrimidin-1-yl)propane, C(25)H(36)N(8)S(4), the pairs of pyrazolo[3,4-d]pyrimidine rings in the molecule stack as a result of intramolecular pi-pi interactions between the heterocyclic rings. The crystal packing also exhibits an intermolecular C--H...pi interaction between one methyl group of an isopropyl group and a pyrazolo[3,4-d]pyrimidine ring.

Intermolecular stacking in pyrazolo[3,4-d]pyrimidine-based pentamethylene-linked flexible molecules.

The crystal structures of 1-[5-[4,6-bis(methylsulfanyl)-2H-pyrazolo[3,4-d]pyrimidin-2-yl]pentyl]-6-methylsulfanyl-4-(pyrrolidin-1-yl)-1H-pyrazolo[3,4-d]pyrimidine, C(22)H(29)N(9)S(3), and 6-methylsulfanyl-1-[5-[6-methylsulfanyl-4-(pyrrolidin-1-yl)-2H-pyrazolo[3,4-d]pyrimidin-2-yl]pentyl]-4-(pyrrolidin-1-yl)-1H-pyrazolo[3,4-d]pyrimidine, C(25)H(34)N(10)S(2), which differ in having either a pyrrolidine substituent or a methylsulfanyl group, show intermolecular stacking due to aromatic pi-pi interactions between the pyrazolo[3,4-d]pyrimidine rings.

A stacked pyrazolo[3,4-d]pyrimidine-based flexible molecule: the effect of a bulky benzyl group on intermolecular stacking in comparison with methyl and ethyl groups.

In the crystal structure of 1,1'-(1,3-propanediyl)bis(5-benzyl-6-methylsulfanyl-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-4-one), C(29)H(28)N(8)O(2)S(2), the pairs of pyrazolo[3,4-d]pyrimidine rings stack as a result of intramolecular pi-pi interactions between the heterocyclic rings. The folded molecules are further stacked in pairs, due to intermolecular aromatic pi-pi interactions and C-H...O hydrogen bonds.

Isomeric pyrazolo[3,4-d]pyrimidine-based molecules: disappearance of dimerization due to interchanged substitutions.

In 5-benzyl-1,7-dimethyl-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d]pyrimidine-4,6-dione, C(14)H(14)N(4)O(2), which crystallizes in space group P 1 macro, weak intermolecular C[bond]H...O hydrogen bonds generate dimers. The isomeric compound 1-benzyl-5,7-dimethyl-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-d]pyrimidine-4,6-dione, C(14)H(14)N(4)O(2), crystallizes in space group P2(1)/n, and shows no such dimerization. Instead, it exhibits C[bond]H...pi interactions with the phenyl ring. In both structures, the molecules are linked by aromatic pi-pi-stacking interactions.

A dimeric layered structure of a 4-oxo-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidine compound.

The title compound, 6-methylsulfanyl-1-(3-phenylpropyl)-4,5-dihydro-1H-pyrazolo[3,4-d]pyrimidin-4-one, C(15)H(16)N(4)OS, crystallizes in space group Pbca, with two molecules of similar structure in the asymmetric unit. The molecular structure shows the absence of intramolecular stacking in the crystalline state, as indicated by earlier (1)H NMR analysis in solution. In addition, the crystal packing reveals the formation of a layered structure, due mainly to intermolecular N[bond]H...O[double bond]C hydrogen bonding and arene-arene interactions.