α,ω-Bis(3,6-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-yl)alkanes and products of their cyclization, pyrimidinophanes: intra- and intermolecular interaction in crystals and in solutions

Unusual Reaction of Macrocyclic Uracils with Paraformaldehyde

“…It should be noted that simple N-substituted uracils afforded C 5 ,C 5Ј -methylene bridged products when heating the uracils at either 100 [6,7] or 140°C for 2 h. [8] Ring-closure reactions of acyclic uracil derivatives with paraformaldehyde were performed in 0.5 m HCl in the presence of Cu 2 Cl 2 at 100°C, and only compounds with a linear structure were found in the absence of the Cu I salt. [9,10] On the contrary, the interaction of pyrimidinophane 1c with paraformaldehyde requires much more severe conditions, and the cyclization is the dominant direction of the process. The reaction of cis isomer 1d with paraformaldehyde in aqueous 1.0 m HCl at 140°C gave pyrimidinophanes of two types.…”

“…In particular, the interaction of α,ω-bis(3,6-dimethyluracil-1-yl)alkanes with paraformaldehyde leads to pyrimidinophanes, which contain two α,ω-bis(3,6-dimethyluracil-1,5-diyl)alkane units bonded to each other through the C 5 atoms of the pyrimidine rings with intermolecular methylene bridges. [10] The yields of these pyrimidinophanes are low, and the acyclic oligomeric products prevail. In fact, whereas the reactions of acyclic bis(3,6-dimethyluracils) with paraformaldehyde result in insignificant yields of pyrimidinophanes with C 5 CH 2 C 5Ј spacers, macrocyclic uracils, especially isomers 1c,d, afford only cyclic products.…”

“…In accordance with the nature of the substituents at C 6 of the uracil moiety, its derivatives react with paraformaldehyde under neutral [6] or acidic [7] conditions to give C 5 ,C 5Ј -methylenebispyrimidines. Reactions resulting in bis-(uracil-5-yl)methanes were used successfully in the preparation of pyrimidinophanes [8][9][10] and metallacalix [4]arenes [11] based on uracil derivatives. Pyrimidinophanes are of interest in connection with the stacking structures in DNA, the formation of pyrimidine photodimers in DNA by ultraviolet light, [12] the mechanistic studies on DNA photolysis, [13] complexation properties, [14,15] and biological activity.…”

“…Pyrimidinophanes are of interest in connection with the stacking structures in DNA, the formation of pyrimidine photodimers in DNA by ultraviolet light, [12] the mechanistic studies on DNA photolysis, [13] complexation properties, [14,15] and biological activity. [16][17][18] A series of pyrimidinophanes with three [9] and four uracil fragments [10] was prepared by ring-closing acid-catalyzed reaction of 1,3-bis[ω-(N-methyluracil-1-yl)alkyl]-thymines and α,β-bis(3,6-dimethyl-uracil-1-yl)alkanes with paraformaldehyde in the presence of copper(I) chloride.…”